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Red Hat Enterprise Linux 8

Setting up and configuring web servers and reverse proxies, network file services, database servers, mail transport agents, and printers

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Abstract

Configure and run the Apache HTTP web server or the NGINX web server on Red Hat Enterprise Linux 8. Configure and use network file services such as Samba or NFS. Install the MariaDB, MySQL, or PostgreSQL database server, configure it, back up and migrate your data. Deploy and configure the Postfix mail transport agent. Configure printing using a CUPS server.

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Chapter 1. Setting up the Apache HTTP web server

1.1. Introduction to the Apache HTTP web server

A web server is a network service that serves content to a client over the web. This typically means web pages, but any other documents can be served as well. Web servers are also known as HTTP servers, as they use the hypertext transport protocol (HTTP).

The Apache HTTP Server, httpd, is an open source web server developed by the Apache Software Foundation.

If you are upgrading from a previous release of Red Hat Enterprise Linux, you have to update the httpd service configuration accordingly. This section reviews some of the newly added features, and guides you through the update of prior configuration files.

1.2. Notable changes in the Apache HTTP Server

The Apache HTTP Server has been updated from version 2.4.6 in RHEL 7 to version 2.4.37 in RHEL 8. This updated version includes several new features, but maintains backwards compatibility with the RHEL 7 version at the level of configuration and Application Binary Interface (ABI) of external modules.

New features include:

  • HTTP/2 support is now provided by the mod_http2 package, which is a part of the httpd module.
  • systemd socket activation is supported. See httpd.socket(8) man page for more details.

  • Multiple new modules have been added:

    • mod_proxy_hcheck - a proxy health-check module
    • mod_proxy_uwsgi - a Web Server Gateway Interface (WSGI) proxy
    • mod_proxy_fdpass - provides support for the passing the socket of the client to another process
    • mod_cache_socache - an HTTP cache using, for example, memcache backend
    • mod_md - an ACME protocol SSL/TLS certificate service

  • The following modules now load by default:

    • mod_request
    • mod_macro
    • mod_watchdog
  • A new subpackage, httpd-filesystem, has been added, which contains the basic directory layout for the Apache HTTP Server including the correct permissions for the directories.
  • Instantiated service support, httpd@.service has been introduced. See the httpd.service man page for more information.
  • A new httpd-init.service replaces the %post script to create a self-signed mod_ssl key pair.
  • Automated TLS certificate provisioning and renewal using the Automatic Certificate Management Environment (ACME) protocol is now supported with the mod_md package (for use with certificate providers such as Let’s Encrypt).
  • The Apache HTTP Server now supports loading TLS certificates and private keys from hardware security tokens directly from PKCS#11 modules. As a result, a mod_ssl configuration can now use PKCS#11 URLs to identify the TLS private key, and, optionally, the TLS certificate in the SSLCertificateKeyFile and SSLCertificateFile directives.

  • A new ListenFree directive in the /etc/httpd/conf/httpd.conf file is now supported.

    Similarly to the Listen directive, ListenFree provides information about IP addresses, ports, or IP address-and-port combinations that the server listens to. However, with ListenFree, the IP_FREEBIND socket option is enabled by default. Hence, httpd is allowed to bind to a nonlocal IP address or to an IP address that does not exist yet. This allows httpd to listen on a socket without requiring the underlying network interface or the specified dynamic IP address to be up at the time when httpd is trying to bind to it.

    Note that the ListenFree directive is currently available only in RHEL 8.

    For more details on ListenFree, see the following table:

    Table 1.1. ListenFree directive’s syntax, status, and modules

    SyntaxStatusModules

    ListenFree [IP-address:]portnumber [protocol]

    MPM

    event, worker, prefork, mpm_winnt, mpm_netware, mpmt_os2

Other notable changes include:

  • The following modules have been removed:

  • The default type of the DBM authentication database used by the Apache HTTP Server in RHEL 8 has been changed from SDBM to db5.
  • The mod_wsgi module for the Apache HTTP Server has been updated to Python 3. WSGI applications are now supported only with Python 3, and must be migrated from Python 2.

  • The multi-processing module (MPM) configured by default with the Apache HTTP Server has changed from a multi-process, forked model (known as prefork) to a high-performance multi-threaded model, event.

    Any third-party modules that are not thread-safe need to be replaced or removed. To change the configured MPM, edit the /etc/httpd/conf.modules.d/00-mpm.conf file. See the httpd.service(8) man page for more information.

  • The minimum UID and GID allowed for users by suEXEC are now 1000 and 500, respectively (previously 100 and 100).
  • The /etc/sysconfig/httpd file is no longer a supported interface for setting environment variables for the httpd service. The httpd.service(8) man page has been added for the systemd service.
  • Stopping the httpd service now uses a “graceful stop” by default.
  • The mod_auth_kerb module has been replaced by the mod_auth_gssapi module.

1.3. Updating the configuration

To update the configuration files from the Apache HTTP Server version used in Red Hat Enterprise Linux 7, choose one of the following options:

  • If /etc/sysconfig/httpd is used to set environment variables, create a systemd drop-in file instead.
  • If any third-party modules are used, ensure they are compatible with a threaded MPM.
  • If suexec is used, ensure user and group IDs meet the new minimums.

You can check the configuration for possible errors by using the following command: 

# apachectl configtest
Syntax OK

1.4. The Apache configuration files

The httpd, by default, reads the configuration files after start. You can see the list of the locations of configuration files in the table below.

Table 1.2. The httpd service configuration files

PathDescription

/etc/httpd/conf/httpd.conf

The main configuration file.

/etc/httpd/conf.d/

An auxiliary directory for configuration files that are included in the main configuration file.

/etc/httpd/conf.modules.d/

An auxiliary directory for configuration files which load installed dynamic modules packaged in Red Hat Enterprise Linux. In the default configuration, these configuration files are processed first.

Although the default configuration is suitable for most situations, you can use also other configuration options. For any changes to take effect, restart the web server first.

To check the configuration for possible errors, type the following at a shell prompt: 

# apachectl configtest
Syntax OK

To make the recovery from mistakes easier, make a copy of the original file before editing it.

1.5. Managing the httpd service

This section describes how to start, stop, and restart the httpd service.

Prerequisites

  • The Apache HTTP Server is installed.

Procedure

  • To start the httpd service, enter: 

    # systemctl start httpd

  • To stop the httpd service, enter: 

    # systemctl stop httpd

  • To restart the httpd service, enter: 

    # systemctl restart httpd

1.6. Setting up a single-instance Apache HTTP Server

You can set up a single-instance Apache HTTP Server to serve static HTML content.

Follow the procedure if the web server should provide the same content for all domains associated with the server. If you want to provide different content for different domains, set up name-based virtual hosts. For details, see Configuring Apache name-based virtual hosts.

Procedure

  1. Install the httpd package: 

    # yum install httpd

  2. If you use firewalld, open the TCP port 80 in the local firewall: 

    # firewall-cmd --permanent --add-port=80/tcp
# firewall-cmd --reload

  3. Enable and start the httpd service: 

    # systemctl enable --now httpd

  4. Optional: Add HTML files to the /var/www/html/ directory.

    Note

    When adding content to /var/www/html/, files and directories must be readable by the user under which httpd runs by default. The content owner can be the either the root user and root user group, or another user or group of the administrator’s choice. If the content owner is the root user and root user group, the files must be readable by other users. The SELinux context for all the files and directories must be httpd_sys_content_t, which is applied by default to all content within the /var/www directory.

Verification steps

  • Connect with a web browser to http://server_IP_or_host_name/.

    If the /var/www/html/ directory is empty or does not contain an index.html or index.htm file, Apache displays the Red Hat Enterprise Linux Test Page. If /var/www/html/ contains HTML files with a different name, you can load them by entering the URL to that file, such as http://server_IP_or_host_name/example.html.

Additional resources

1.7. Configuring Apache name-based virtual hosts

Name-based virtual hosts enable Apache to serve different content for different domains that resolve to the IP address of the server.

You can set up a virtual host for both the example.com and example.net domain with separate document root directories. Both virtual hosts serve static HTML content.

Prerequisites

  • Clients and the web server resolve the example.com and example.net domain to the IP address of the web server.

    Note that you must manually add these entries to your DNS server.

Procedure

  1. Install the httpd package: 

    # yum install httpd

  2. Edit the /etc/httpd/conf/httpd.conf file:

    1. Append the following virtual host configuration for the example.com domain: 

      <VirtualHost *:80>
    DocumentRoot "/var/www/example.com/"
    ServerName example.com
    CustomLog /var/log/httpd/example.com_access.log combined
    ErrorLog /var/log/httpd/example.com_error.log
</VirtualHost>

      These settings configure the following:

      • All settings in the <VirtualHost *:80> directive are specific for this virtual host.
      • DocumentRoot sets the path to the web content of the virtual host.

      • ServerName sets the domains for which this virtual host serves content.

        To set multiple domains, add the ServerAlias parameter to the configuration and specify the additional domains separated with a space in this parameter.

      • CustomLog sets the path to the access log of the virtual host.

      • ErrorLog sets the path to the error log of the virtual host.

        Note

        Apache uses the first virtual host found in the configuration also for requests that do not match any domain set in the ServerName and ServerAlias parameters. This also includes requests sent to the IP address of the server.

  3. Append a similar virtual host configuration for the example.net domain: 

    <VirtualHost *:80>
    DocumentRoot "/var/www/example.net/"
    ServerName example.net
    CustomLog /var/log/httpd/example.net_access.log combined
    ErrorLog /var/log/httpd/example.net_error.log
</VirtualHost>

  4. Create the document roots for both virtual hosts: 

    # mkdir /var/www/example.com/
# mkdir /var/www/example.net/

  5. If you set paths in the DocumentRoot parameters that are not within /var/www/, set the httpd_sys_content_t context on both document roots: 

    # semanage fcontext -a -t httpd_sys_content_t "/srv/example.com(/.*)?"
# restorecon -Rv /srv/example.com/
# semanage fcontext -a -t httpd_sys_content_t "/srv/example.net(/.\*)?"
# restorecon -Rv /srv/example.net/

    These commands set the httpd_sys_content_t context on the /srv/example.com/ and /srv/example.net/ directory.

    Note that you must install the policycoreutils-python-utils package to run the restorecon command.

  6. If you use firewalld, open port 80 in the local firewall: 

    # firewall-cmd --permanent --add-port=80/tcp
# firewall-cmd --reload

  7. Enable and start the httpd service: 

    # systemctl enable --now httpd

Verification steps

  1. Create a different example file in each virtual host’s document root: 

    # echo "vHost example.com" > /var/www/example.com/index.html
# echo "vHost example.net" > /var/www/example.net/index.html
  2. Use a browser and connect to http://example.com. The web server shows the example file from the example.com virtual host.
  3. Use a browser and connect to http://example.net. The web server shows the example file from the example.net virtual host.

Additional resources

1.8. Configuring Kerberos authentication for the Apache HTTP web server

To perform Kerberos authentication in the Apache HTTP web server, RHEL 8 uses the mod_auth_gssapi Apache module. The Generic Security Services API (GSSAPI) is an interface for applications that make requests to use security libraries, such as Kerberos. The gssproxy service allows to implement privilege separation for the httpd server, which optimizes this process from the security point of view.

Note

The mod_auth_gssapi module replaces the removed mod_auth_kerb module.

Prerequisites

  • The httpd and gssproxy packages are installed.
  • The Apache web server is set up and the httpd service is running.

1.8.1. Setting up GSS-Proxy in an IdM environment

This procedure describes how to set up GSS-Proxy to perform Kerberos authentication in the Apache HTTP web server.

Procedure

  1. Enable access to the keytab file of HTTP/<SERVER_NAME>@realm principal by creating the service principal: 

    # ipa service-add HTTP/<SERVER_NAME>

  2. Retrieve the keytab for the principal stored in the /etc/gssproxy/http.keytab file: 

    # ipa-getkeytab -s $(awk '/^server =/ {print $3}' /etc/ipa/default.conf) -k /etc/gssproxy/http.keytab -p HTTP/$(hostname -f)

    This step sets permissions to 400, thus only the root user has access to the keytab file. The apache user does not.

  3. Create the /etc/gssproxy/80-httpd.conf file with the following content: 

    [service/HTTP]
  mechs = krb5
  cred_store = keytab:/etc/gssproxy/http.keytab
  cred_store = ccache:/var/lib/gssproxy/clients/krb5cc_%U
  euid = apache

  4. Restart and enable the gssproxy service: 

    # systemctl restart gssproxy.service
# systemctl enable gssproxy.service

Additional resources

  • gssproxy(8) man pages
  • gssproxy-mech(8) man pages
  • gssproxy.conf(5) man pages

1.8.2. Configuring Kerberos authentication for a directory shared by the Apache HTTP web server

This procedure describes how to configure Kerberos authentication for the /var/www/html/private/ directory.

Prerequisites

  • The gssproxy service is configured and running.

Procedure

  1. Configure the mod_auth_gssapi module to protect the /var/www/html/private/ directory: 

    <Location /var/www/html/private>
  AuthType GSSAPI
  AuthName "GSSAPI Login"
  Require valid-user
</Location>

  2. Create the /etc/systemd/system/httpd.service file with the following content: 

    .include /lib/systemd/system/httpd.service
[Service]
Environment=GSS_USE_PROXY=1

  3. Reload the systemd configuration: 

    # systemctl daemon-reload

  4. Restart the httpd service: 

    # systemctl restart httpd.service

Verification steps

  1. Obtain a Kerberos ticket: 

    # kinit
  2. Open the URL to the protected directory in a browser.

1.9. Configuring TLS encryption on an Apache HTTP Server

By default, Apache provides content to clients using an unencrypted HTTP connection. This section describes how to enable TLS encryption and configure frequently used encryption-related settings on an Apache HTTP Server.

Prerequisites

  • The Apache HTTP Server is installed and running.

1.9.1. Adding TLS encryption to an Apache HTTP Server

You can enable TLS encryption on an Apache HTTP Server for the example.com domain.

Prerequisites

  • The Apache HTTP Server is installed and running.

  • The private key is stored in the /etc/pki/tls/private/example.com.key file.

    For details about creating a private key and certificate signing request (CSR), as well as how to request a certificate from a certificate authority (CA), see your CA’s documentation. Alternatively, if your CA supports the ACME protocol, you can use the mod_md module to automate retrieving and provisioning TLS certificates.

  • The TLS certificate is stored in the /etc/pki/tls/certs/example.com.crt file. If you use a different path, adapt the corresponding steps of the procedure.
  • The CA certificate is stored in the /etc/pki/tls/certs/ca.crt file. If you use a different path, adapt the corresponding steps of the procedure.
  • Clients and the web server resolve the host name of the server to the IP address of the web server.

Procedure

  1. Install the mod_ssl package:

    # yum install mod_ssl

  2. Edit the /etc/httpd/conf.d/ssl.conf file and add the following settings to the <VirtualHost _default_:443> directive:

    1. Set the server name:

      ServerName example.com

    Important

    The server name must match the entry set in the Common Name field of the certificate.

    1. Optional: If the certificate contains additional host names in the Subject Alt Names (SAN) field, you can configure mod_ssl to provide TLS encryption also for these host names. To configure this, add the ServerAliases parameter with corresponding names:

      ServerAlias www.example.com server.example.com

    2. Set the paths to the private key, the server certificate, and the CA certificate:

      SSLCertificateKeyFile "/etc/pki/tls/private/example.com.key"SSLCertificateFile "/etc/pki/tls/certs/example.com.crt"SSLCACertificateFile "/etc/pki/tls/certs/ca.crt"

  3. For security reasons, configure that only the root user can access the private key file:

    # chown root:root /etc/pki/tls/private/example.com.key # chmod 600 /etc/pki/tls/private/example.com.key

    Warning

    If the private key was accessed by unauthorized users, revoke the certificate, create a new private key, and request a new certificate. Otherwise, the TLS connection is no longer secure.

  4. If you use firewalld, open port 443 in the local firewall:

    # firewall-cmd --permanent --add-port=443/tcp # firewall-cmd --reload

  5. Restart the httpd service:

    # systemctl restart httpd

    Note

    If you protected the private key file with a password, you must enter this password each time when the httpd service starts.

Verification steps

  • Use a browser and connect to https://example.com.

Additional resources

1.9.2. Setting the supported TLS protocol versions on an Apache HTTP Server

By default, the Apache HTTP Server on RHEL uses the system-wide crypto policy that defines safe default values, which are also compatible with recent browsers. For example, the DEFAULT policy defines that only the TLSv1.2 and TLSv1.3 protocol versions are enabled in apache.

You can manually configure which TLS protocol versions your Apache HTTP Server supports. Follow the procedure if your environment requires to enable only specific TLS protocol versions, for example:

  • If your environment requires that clients can also use the weak TLS1 (TLSv1.0) or TLS1.1 protocol.
  • If you want to configure that Apache only supports the TLSv1.2 or TLSv1.3 protocol.

Prerequisites

Procedure

  1. Edit the /etc/httpd/conf/httpd.conf file, and add the following setting to the <VirtualHost> directive for which you want to set the TLS protocol version. For example, to enable only the TLSv1.3 protocol: 

    SSLProtocol -All TLSv1.3

  2. Restart the httpd service: 

    # systemctl restart httpd

Verification steps

  1. Use the following command to verify that the server supports TLSv1.3: 

    # openssl s_client -connect example.com:443 -tls1_3

  2. Use the following command to verify that the server does not support TLSv1.2: 

    # openssl s_client -connect example.com:443 -tls1_2

    If the server does not support the protocol, the command returns an error: 

    140111600609088:error:1409442E:SSL routines:ssl3_read_bytes:tlsv1 alert protocol version:ssl/record/rec_layer_s3.c:1543:SSL alert number 70
  3. Optional: Repeat the command for other TLS protocol versions.

Additional resources

1.9.3. Setting the supported ciphers on an Apache HTTP Server

By default, the Apache HTTP Server uses the system-wide crypto policy that defines safe default values, which are also compatible with recent browsers. For the list of ciphers the system-wide crypto allows, see the /etc/crypto-policies/back-ends/openssl.config file.

You can manually configure which ciphers your Apache HTTP Server supports. Follow the procedure if your environment requires specific ciphers.

Prerequisites

Procedure

  1. Edit the /etc/httpd/conf/httpd.conf file, and add the SSLCipherSuite parameter to the <VirtualHost> directive for which you want to set the TLS ciphers: 

    SSLCipherSuite "EECDH+AESGCM:EDH+AESGCM:AES256+EECDH:AES256+EDH:!SHA1:!SHA256"

    This example enables only the EECDH+AESGCM, EDH+AESGCM, AES256+EECDH, and AES256+EDH ciphers and disables all ciphers which use the SHA1 and SHA256 message authentication code (MAC).

  2. Restart the httpd service: 

    # systemctl restart httpd

Verification steps

  1. To display the list of ciphers the Apache HTTP Server supports:

    1. Install the nmap package: 

      # yum install nmap

    2. Use the nmap utility to display the supported ciphers: 

      # nmap --script ssl-enum-ciphers -p 443 example.com
...
PORT    STATE SERVICE
443/tcp open  https
| ssl-enum-ciphers:
|   TLSv1.2:
|     ciphers:
|       TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (ecdh_x25519) - A
|       TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 (dh 2048) - A
|       TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256 (ecdh_x25519) - A
...

Additional resources

1.10. Configuring TLS client certificate authentication

Client certificate authentication enables administrators to allow only users who authenticate using a certificate to access resources on the web server. You can configure client certificate authentication for the /var/www/html/Example/ directory.

If the Apache HTTP Server uses the TLS 1.3 protocol, certain clients require additional configuration. For example, in Firefox, set the security.tls.enable_post_handshake_auth parameter in the about:config menu to true. For further details, see Transport Layer Security version 1.3 in Red Hat Enterprise Linux 8.

Prerequisites

Procedure

  1. Edit the /etc/httpd/conf/httpd.conf file and add the following settings to the <VirtualHost> directive for which you want to configure client authentication: 

    <Directory "/var/www/html/Example/">
  SSLVerifyClient require
</Directory>

    The SSLVerifyClient require setting defines that the server must successfully validate the client certificate before the client can access the content in the /var/www/html/Example/ directory.

  2. Restart the httpd service: 

    # systemctl restart httpd

Verification steps

  1. Use the curl utility to access the https://example.com/Example/ URL without client authentication: 

    $ curl https://example.com/Example/
curl: (56) OpenSSL SSL_read: error:1409445C:SSL routines:ssl3_read_bytes:tlsv13 alert certificate required, errno 0

    The error indicates that the web server requires a client certificate authentication.

  2. Pass the client private key and certificate, as well as the CA certificate to curl to access the same URL with client authentication: 

    $ curl --cacert ca.crt --key client.key --cert client.crt https://example.com/Example/

    If the request succeeds, curl displays the index.html file stored in the /var/www/html/Example/ directory.

Additional resources

1.11. Securing web applications on a web server using ModSecurity

ModSecurity is an open source web application firewall (WAF) supported by various web servers such as Apache, Nginx, and IIS, which reduces security risks in web applications. ModSecurity provides customizable rule sets for configuring your server.

The mod_security-crs package contains the core rule set (CRS) with rules against cross-website scripting, bad user agents, SQL injection, Trojans, session hijacking, and other exploits.

1.11.1. Deploying the ModSecurity web-based application firewall for Apache

To reduce risks related to running web-based applications on your web server by deploying ModSecurity, install the mod_security and mod_security_crs packages for the Apache HTTP server. The mod_security_crs package provides the core rule set (CRS) for the ModSecurity web-based application firewall (WAF) module.

Procedure

  1. Install the mod_security, mod_security_crs, and httpd packages: 

    # yum install -y mod_security mod_security_crs httpd

  2. Start the httpd server: 

    # systemctl restart httpd

Verification

  1. Verify that the ModSecurity web-based application firewall is enabled on your Apache HTTP server: 

    # httpd -M | grep security
 security2_module (shared)

  2. Check that the /etc/httpd/modsecurity.d/activated_rules/ directory contains rules provided by mod_security_crs: 

    # ls /etc/httpd/modsecurity.d/activated_rules/
...
REQUEST-921-PROTOCOL-ATTACK.conf
REQUEST-930-APPLICATION-ATTACK-LFI.conf
...

Additional resources

1.11.2. Adding a custom rule to ModSecurity

If the rules contained in the ModSecurity core rule set (CRS) do not fit your scenario and if you want to prevent additional possible attacks, you can add your custom rules to the rule set used by the ModSecurity web-based application firewall. The following example demonstrates the addition of a simple rule. For creating more complex rules, see the reference manual on the ModSecurity Wiki website.

Prerequisites

  • ModSecurity for Apache is installed and enabled.

Procedure

  1. Open the /etc/httpd/conf.d/mod_security.conf file in a text editor of your choice, for example: 

    # vi /etc/httpd/conf.d/mod_security.conf

  2. Add the following example rule after the line starting with SecRuleEngine On: 

    SecRule ARGS:data "@contains evil" "deny,status:403,msg:'param data contains evil data',id:1"

    The previous rule forbids the use of resources to the user if the data parameter contains the evil string.

  3. Save the changes, and quit the editor.

  4. Restart the httpd server: 

    # systemctl restart httpd

Verification

  1. Create a test.html page: 

    # echo "mod_security test" > /var/www/html/test.html

  2. Restart the httpd server: 

    # systemctl restart httpd

  3. Request test.html without malicious data in the GET variable of the HTTP request: 

    $ curl http://localhost/test.html?data=good

mod_security test

  4. Request test.html with malicious data in the GET variable of the HTTP request: 

    $ curl localhost/test.html?data=xxxevilxxx

<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<html><head>
<title>403 Forbidden</title>
</head><body>
<h1>Forbidden</h1>
<p>You don't have permission to access this resource.</p>
</body></html>

  5. Check the /var/log/httpd/error_log file, and locate the log entry about denying access with the param data containing an evil data message: 

    [Wed May 25 08:01:31.036297 2022] [:error] [pid 5839:tid 139874434791168] [client ::1:45658] [client ::1] ModSecurity: Access denied with code 403 (phase 2). String match "evil" at ARGS:data. [file "/etc/httpd/conf.d/mod_security.conf"] [line "4"] [id "1"] [msg "param data contains evil data"] [hostname "localhost"] [uri "/test.html"] [unique_id "Yo4amwIdsBG3yZqSzh2GuwAAAIY"]

Additional resources

1.12. Installing the Apache HTTP Server manual

You can install the Apache HTTP Server manual. This manual provides a detailed documentation of, for example:

  • Configuration parameters and directives
  • Performance tuning
  • Authentication settings
  • Modules
  • Content caching
  • Security tips
  • Configuring TLS encryption

After installing the manual, you can display it using a web browser.

Prerequisites

  • The Apache HTTP Server is installed and running.

Procedure

  1. Install the httpd-manual package: 

    # yum install httpd-manual

  2. Optional: By default, all clients connecting to the Apache HTTP Server can display the manual. To restrict access to a specific IP range, such as the 192.0.2.0/24 subnet, edit the /etc/httpd/conf.d/manual.conf file and add the Require ip 192.0.2.0/24 setting to the <Directory "/usr/share/httpd/manual"> directive: 

    <Directory "/usr/share/httpd/manual">
...
    Require ip 192.0.2.0/24
...
</Directory>

  3. Restart the httpd service: 

    # systemctl restart httpd

Verification steps

  1. To display the Apache HTTP Server manual, connect with a web browser to http://host_name_or_IP_address/manual/

1.13. Working with Apache modules

The httpd service is a modular application, and you can extend it with a number of Dynamic Shared Objects (DSOs). Dynamic Shared Objects are modules that you can dynamically load or unload at runtime as necessary. You can find these modules in the /usr/lib64/httpd/modules/ directory.

1.13.1. Loading a DSO module

As an administrator, you can choose the functionality to include in the server by configuring which modules the server should load. To load a particular DSO module, use the LoadModule directive. Note that modules provided by a separate package often have their own configuration file in the /etc/httpd/conf.modules.d/ directory.

Prerequisites

  • You have installed the httpd package.

Procedure

  1. Search for the module name in the configuration files in the /etc/httpd/conf.modules.d/ directory: 

    # grep mod_ssl.so /etc/httpd/conf.modules.d/*

  2. Edit the configuration file in which the module name was found, and uncomment the LoadModule directive of the module: 

    LoadModule ssl_module modules/mod_ssl.so

  3. If the module was not found, for example, because a RHEL package does not provide the module, create a configuration file, such as /etc/httpd/conf.modules.d/30-example.conf with the following directive: 

    LoadModule ssl_module modules/<custom_module>.so

  4. Restart the httpd service: 

    # systemctl restart httpd

1.13.2. Compiling a custom Apache module

You can create your own module and build it with the help of the httpd-devel package, which contains the include files, the header files, and the APache eXtenSion (apxs) utility required to compile a module.

Prerequisites

  • You have the httpd-devel package installed.

Procedure

  • Build a custom module with the following command: 

    # apxs -i -a -c module_name.c

Verification steps

1.14. Exporting a private key and certificates from an NSS database to use them in an Apache web server configuration

RHEL 8 no longer provides the mod_nss module for the Apache web server, and Red Hat recommends using the mod_ssl module. If you store your private key and certificates in a Network Security Services (NSS) database, for example, because you migrated the web server from RHEL 7 to RHEL 8, follow this procedure to extract the key and certificates in Privacy Enhanced Mail (PEM) format. You can then use the files in the mod_ssl configuration as described in Configuring TLS encryption on an Apache HTTP server.

This procedure assumes that the NSS database is stored in /etc/httpd/alias/ and that you store the exported private key and certificates in the /etc/pki/tls/ directory.

Prerequisites

  • The private key, the certificate, and the certificate authority (CA) certificate are stored in an NSS database.

Procedure

  1. List the certificates in the NSS database: 

    # certutil -d /etc/httpd/alias/ -L
Certificate Nickname           Trust Attributes
                               SSL,S/MIME,JAR/XPI

Example CA                     C,,
Example Server Certificate     u,u,u

    You need the nicknames of the certificates in the next steps.

  2. To extract the private key, you must temporarily export the key to a PKCS #12 file:

    1. Use the nickname of the certificate associated with the private key, to export the key to a PKCS #12 file: 

      # pk12util -o /etc/pki/tls/private/export.p12 -d /etc/httpd/alias/ -n "Example Server Certificate"
Enter password for PKCS12 file: password
Re-enter password: password
pk12util: PKCS12 EXPORT SUCCESSFUL

      Note that you must set a password on the PKCS #12 file. You need this password in the next step.

    2. Export the private key from the PKCS #12 file: 

      # openssl pkcs12 -in /etc/pki/tls/private/export.p12 -out /etc/pki/tls/private/server.key -nocerts -nodes
Enter Import Password: password
MAC verified OK

    3. Delete the temporary PKCS #12 file: 

      # rm /etc/pki/tls/private/export.p12

  3. Set the permissions on /etc/pki/tls/private/server.key to ensure that only the root user can access this file: 

    # chown root:root /etc/pki/tls/private/server.key
# chmod 0600 /etc/pki/tls/private/server.key

  4. Use the nickname of the server certificate in the NSS database to export the CA certificate: 

    # certutil -d /etc/httpd/alias/ -L -n "Example Server Certificate" -a -o /etc/pki/tls/certs/server.crt

  5. Set the permissions on /etc/pki/tls/certs/server.crt to ensure that only the root user can access this file: 

    # chown root:root /etc/pki/tls/certs/server.crt
# chmod 0600 /etc/pki/tls/certs/server.crt

  6. Use the nickname of the CA certificate in the NSS database to export the CA certificate: 

    # certutil -d /etc/httpd/alias/ -L -n "Example CA" -a -o /etc/pki/tls/certs/ca.crt

  7. Follow Configuring TLS encryption on an Apache HTTP server to configure the Apache web server, and:

    • Set the SSLCertificateKeyFile parameter to /etc/pki/tls/private/server.key.
    • Set the SSLCertificateFile parameter to /etc/pki/tls/certs/server.crt.
    • Set the SSLCACertificateFile parameter to /etc/pki/tls/certs/ca.crt.

Additional resources

  • certutil(1) man page
  • pk12util(1) man page
  • pkcs12(1ssl) man page

1.15. Additional resources

Chapter 2. Setting up and configuring NGINX

NGINX is a high performance and modular server that you can use, for example, as a:

  • Web server
  • Reverse proxy
  • Load balancer

This section describes how to NGINX in these scenarios.

2.1. Installing and preparing NGINX

Red Hat uses Application Streams to provide different versions of NGINX. You can do the following:

  • Select a stream and install NGINX
  • Open the required ports in the firewall
  • Enable and start the nginx service

Using the default configuration, NGINX runs as a web server on port 80 and provides content from the /usr/share/nginx/html/ directory.

Prerequisites

  • RHEL 8 is installed.
  • The host is subscribed to the Red Hat Customer Portal.
  • The firewalld service is enabled and started.

Procedure

  1. Display the available NGINX module streams: 

    # yum module list nginx
Red Hat Enterprise Linux 8 for x86_64 - AppStream (RPMs)
Name        Stream        Profiles        Summary
nginx       1.14 [d]      common [d]      nginx webserver
nginx       1.16          common [d]      nginx webserver
...

Hint: [d]efault, [e]nabled, [x]disabled, [i]nstalled

  2. If you want to install a different stream than the default, select the stream: 

    # yum module enable nginx:stream_version

  3. Install the nginx package: 

    # yum install nginx

  4. Open the ports on which NGINX should provide its service in the firewall. For example, to open the default ports for HTTP (port 80) and HTTPS (port 443) in firewalld, enter: 

    # firewall-cmd --permanent --add-port={80/tcp,443/tcp}
# firewall-cmd --reload

  5. Enable the nginx service to start automatically when the system boots: 

    # systemctl enable nginx

  6. Optionally, start the nginx service: 

    # systemctl start nginx

    If you do not want to use the default configuration, skip this step, and configure NGINX accordingly before you start the service.

Verification steps

  1. Use the yum utility to verify that the nginx package is installed: 

    # yum list installed nginx
Installed Packages
nginx.x86_64    1:1.14.1-9.module+el8.0.0+4108+af250afe    @rhel-8-for-x86_64-appstream-rpms

  2. Ensure that the ports on which NGINX should provide its service are opened in the firewalld: 

    # firewall-cmd --list-ports
80/tcp 443/tcp

  3. Verify that the nginx service is enabled: 

    # systemctl is-enabled nginx
enabled

Additional resources

2.2. Configuring NGINX as a web server that provides different content for different domains

By default, NGINX acts as a web server that provides the same content to clients for all domain names associated with the IP addresses of the server. This procedure explains how to configure NGINX:

  • To serve requests to the example.com domain with content from the /var/www/example.com/ directory
  • To serve requests to the example.net domain with content from the /var/www/example.net/ directory
  • To serve all other requests, for example, to the IP address of the server or to other domains associated with the IP address of the server, with content from the /usr/share/nginx/html/ directory

Prerequisites

  • NGINX is installed

  • Clients and the web server resolve the example.com and example.net domain to the IP address of the web server.

    Note that you must manually add these entries to your DNS server.

Procedure

  1. Edit the /etc/nginx/nginx.conf file:

    1. By default, the /etc/nginx/nginx.conf file already contains a catch-all configuration. If you have deleted this part from the configuration, re-add the following server block to the http block in the /etc/nginx/nginx.conf file: 

      server {
    listen       80 default_server;
    listen       [::]:80 default_server;
    server_name  _;
    root         /usr/share/nginx/html;
}

      These settings configure the following:

      • The listen directive define which IP address and ports the service listens. In this case, NGINX listens on port 80 on both all IPv4 and IPv6 addresses. The default_server parameter indicates that NGINX uses this server block as the default for requests matching the IP addresses and ports.
      • The server_name parameter defines the host names for which this server block is responsible. Setting server_name to _ configures NGINX to accept any host name for this server block.
      • The root directive sets the path to the web content for this server block.

    2. Append a similar server block for the example.com domain to the http block: 

      server {
    server_name  example.com;
    root         /var/www/example.com/;
    access_log   /var/log/nginx/example.com/access.log;
    error_log    /var/log/nginx/example.com/error.log;
}
      • The access_log directive defines a separate access log file for this domain.
      • The error_log directive defines a separate error log file for this domain.

    3. Append a similar server block for the example.net domain to the http block: 

      server {
    server_name  example.net;
    root         /var/www/example.net/;
    access_log   /var/log/nginx/example.net/access.log;
    error_log    /var/log/nginx/example.net/error.log;
}

  2. Create the root directories for both domains: 

    # mkdir -p /var/www/example.com/
# mkdir -p /var/www/example.net/

  3. Set the httpd_sys_content_t context on both root directories: 

    # semanage fcontext -a -t httpd_sys_content_t "/var/www/example.com(/.*)?"
# restorecon -Rv /var/www/example.com/
# semanage fcontext -a -t httpd_sys_content_t "/var/www/example.net(/.\*)?"
# restorecon -Rv /var/www/example.net/

    These commands set the httpd_sys_content_t context on the /var/www/example.com/ and /var/www/example.net/ directories.

    Note that you must install the policycoreutils-python-utils package to run the restorecon commands.

  4. Create the log directories for both domains: 

    # mkdir /var/log/nginx/example.com/
# mkdir /var/log/nginx/example.net/

  5. Restart the nginx service: 

    # systemctl restart nginx

Verification steps

  1. Create a different example file in each virtual host’s document root: 

    # echo "Content for example.com" > /var/www/example.com/index.html
# echo "Content for example.net" > /var/www/example.net/index.html
# echo "Catch All content" > /usr/share/nginx/html/index.html
  2. Use a browser and connect to http://example.com. The web server shows the example content from the /var/www/example.com/index.html file.
  3. Use a browser and connect to http://example.net. The web server shows the example content from the /var/www/example.net/index.html file.
  4. Use a browser and connect to http://IP_address_of_the_server. The web server shows the example content from the /usr/share/nginx/html/index.html file.

2.3. Adding TLS encryption to an NGINX web server

You can enable TLS encryption on an NGINX web server for the example.com domain.

Prerequisites

  • NGINX is installed.

  • The private key is stored in the /etc/pki/tls/private/example.com.key file.

    For details about creating a private key and certificate signing request (CSR), as well as how to request a certificate from a certificate authority (CA), see your CA’s documentation.

  • The TLS certificate is stored in the /etc/pki/tls/certs/example.com.crt file. If you use a different path, adapt the corresponding steps of the procedure.
  • The CA certificate has been appended to the TLS certificate file of the server.
  • Clients and the web server resolve the host name of the server to the IP address of the web server.
  • Port 443 is open in the local firewall.

Procedure

  1. Edit the /etc/nginx/nginx.conf file, and add the following server block to the http block in the configuration: 

    server {
    listen              443 ssl;
    server_name         example.com;
    root                /usr/share/nginx/html;
    ssl_certificate     /etc/pki/tls/certs/example.com.crt;
    ssl_certificate_key /etc/pki/tls/private/example.com.key;
}

  2. For security reasons, configure that only the root user can access the private key file: 

    # chown root:root /etc/pki/tls/private/example.com.key
# chmod 600 /etc/pki/tls/private/example.com.key
    Warning

    If the private key was accessed by unauthorized users, revoke the certificate, create a new private key, and request a new certificate. Otherwise, the TLS connection is no longer secure.

  3. Restart the nginx service: 

    # systemctl restart nginx

Verification steps

  • Use a browser and connect to https://example.com

Additional resources

2.4. Configuring NGINX as a reverse proxy for the HTTP traffic

You can configure the NGINX web server to act as a reverse proxy for HTTP traffic. For example, you can use this functionality to forward requests to a specific subdirectory on a remote server. From the client perspective, the client loads the content from the host it accesses. However, NGINX loads the actual content from the remote server and forwards it to the client.

This procedure explains how to forward traffic to the /example directory on the web server to the URL https://example.com.

Prerequisites

Procedure

  1. Edit the /etc/nginx/nginx.conf file and add the following settings to the server block that should provide the reverse proxy: 

    location /example {
    proxy_pass https://example.com;
}

    The location block defines that NGINX passes all requests in the /example directory to https://example.com.

  2. Set the httpd_can_network_connect SELinux boolean parameter to 1 to configure that SELinux allows NGINX to forward traffic: 

    # setsebool -P httpd_can_network_connect 1

  3. Restart the nginx service: 

    # systemctl restart nginx

Verification steps

  • Use a browser and connect to http://host_name/example and the content of https://example.com is shown.

2.5. Configuring NGINX as an HTTP load balancer

You can use the NGINX reverse proxy feature to load-balance traffic. This procedure describes how to configure NGINX as an HTTP load balancer that sends requests to different servers, based on which of them has the least number of active connections. If both servers are not available, the procedure also defines a third host for fallback reasons.

Prerequisites

Procedure

  1. Edit the /etc/nginx/nginx.conf file and add the following settings: 

    http {
    upstream backend {
        least_conn;
        server server1.example.com;
        server server2.example.com;
        server server3.example.com backup;
    }

    server {
        location / {
            proxy_pass http://backend;
        }
    }
}

    The least_conn directive in the host group named backend defines that NGINX sends requests to server1.example.com or server2.example.com, depending on which host has the least number of active connections. NGINX uses server3.example.com only as a backup in case that the other two hosts are not available.

    With the proxy_pass directive set to http://backend, NGINX acts as a reverse proxy and uses the backend host group to distribute requests based on the settings of this group.

    Instead of the least_conn load balancing method, you can specify:

    • No method to use round robin and distribute requests evenly across servers.
    • ip_hash to send requests from one client address to the same server based on a hash calculated from the first three octets of the IPv4 address or the whole IPv6 address of the client.
    • hash to determine the server based on a user-defined key, which can be a string, a variable, or a combination of both. The consistent parameter configures that NGINX distributes requests across all servers based on the user-defined hashed key value.
    • random to send requests to a randomly selected server.

  2. Restart the nginx service: 

    # systemctl restart nginx

2.6. Additional resources

Chapter 3. Using Samba as a server

Samba implements the Server Message Block (SMB) protocol in Red Hat Enterprise Linux. The SMB protocol is used to access resources on a server, such as file shares and shared printers. Additionally, Samba implements the Distributed Computing Environment Remote Procedure Call (DCE RPC) protocol used by Microsoft Windows.

You can run Samba as:

  • An Active Directory (AD) or NT4 domain member
  • A standalone server

  • An NT4 Primary Domain Controller (PDC) or Backup Domain Controller (BDC)

    Note

    Red Hat supports the PDC and BDC modes only in existing installations with Windows versions which support NT4 domains. Red Hat recommends not setting up a new Samba NT4 domain, because Microsoft operating systems later than Windows 7 and Windows Server 2008 R2 do not support NT4 domains.

    Red Hat does not support running Samba as an AD domain controller (DC).

Independently of the installation mode, you can optionally share directories and printers. This enables Samba to act as a file and print server.

3.1. Understanding the different Samba services and modes

This section describes the different services included in Samba and the different modes you can configure.

3.1.1. The Samba services

Samba provides the following services:

smbd

This service provides file sharing and printing services using the SMB protocol. Additionally, the service is responsible for resource locking and for authenticating connecting users. For authenticating domain members, smbd requires winbindd. The smb systemd service starts and stops the smbd daemon.

To use the smbd service, install the samba package.

nmbd

This service provides host name and IP resolution using the NetBIOS over IPv4 protocol. Additionally to the name resolution, the nmbd service enables browsing the SMB network to locate domains, work groups, hosts, file shares, and printers. For this, the service either reports this information directly to the broadcasting client or forwards it to a local or master browser. The nmb systemd service starts and stops the nmbd daemon.

Note that modern SMB networks use DNS to resolve clients and IP addresses. For Kerberos a working DNS setup is required.

To use the nmbd service, install the samba package.

winbindd

This service provides an interface for the Name Service Switch (NSS) to use AD or NT4 domain users and groups on the local system. This enables, for example, domain users to authenticate to services hosted on a Samba server or to other local services. The winbind systemd service starts and stops the winbindd daemon.

If you set up Samba as a domain member, winbindd must be started before the smbd service. Otherwise, domain users and groups are not available to the local system..

To use the winbindd service, install the samba-winbind package.

Important

Red Hat only supports running Samba as a server with the winbindd service to provide domain users and groups to the local system. Due to certain limitations, such as missing Windows access control list (ACL) support and NT LAN Manager (NTLM) fallback, SSSD is not supported.

3.1.2. The Samba security services

The security parameter in the [global] section in the /etc/samba/smb.conf file manages how Samba authenticates users that are connecting to the service. Depending on the mode you install Samba in, the parameter must be set to different values:

On an AD domain member, set security = ads

In this mode, Samba uses Kerberos to authenticate AD users.

For details about setting up Samba as a domain member, see Setting up Samba as an AD domain member server.

On a standalone server, set security = user

In this mode, Samba uses a local database to authenticate connecting users.

For details about setting up Samba as a standalone server, see Setting up Samba as a standalone server.

On an NT4 PDC or BDC, set security = user
In this mode, Samba authenticates users to a local or LDAP database.
On an NT4 domain member, set security = domain

In this mode, Samba authenticates connecting users to an NT4 PDC or BDC. You cannot use this mode on AD domain members.

For details about setting up Samba as a domain member, see Setting up Samba as an AD domain member server.

Additional resources

  • security parameter in the smb.conf(5) man page

3.1.3. Scenarios when Samba services and Samba client utilities load and reload their configuration

The following describes when Samba services and utilities load and reload their configuration:

  • Samba services reload their configuration:

    • Automatically every 3 minutes
    • On manual request, for example, when you run the smbcontrol all reload-config command.
  • Samba client utilities read their configuration only when you start them.

Note that certain parameters, such as security require a restart of the smb service to take effect and a reload is not sufficient.

Additional resources

  • The How configuration changes are applied section in the smb.conf(5) man page
  • The smbd(8), nmbd(8), and winbindd(8) man pages

3.1.4. Editing the Samba configuration in a safe way

Samba services automatically reload their configuration every 3 minutes. This procedure describes how to edit the Samba configuration in a way that prevents the services reload the changes before you have verified the configuration using the testparm utility.

Prerequisites

  • Samba is installed.

Procedure

  1. Create a copy of the /etc/samba/smb.conf file: 

    # cp /etc/samba/smb.conf /etc/samba/samba.conf.copy
  2. Edit the copied file and make the desired changes.

  3. Verify the configuration in the /etc/samba/samba.conf.copy file: 

    # testparm -s /etc/samba/samba.conf.copy

    If testparm reports errors, fix them and run the command again.

  4. Override the /etc/samba/smb.conf file with the new configuration: 

    # mv /etc/samba/samba.conf.copy /etc/samba/smb.conf

  5. Wait until the Samba services automatically reload their configuration or manually reload the configuration: 

    # smbcontrol all reload-config

Additional resources

3.2. Verifying the smb.conf file by using the testparm utility

The testparm utility verifies that the Samba configuration in the /etc/samba/smb.conf file is correct. The utility detects invalid parameters and values, but also incorrect settings, such as for ID mapping. If testparm reports no problem, the Samba services will successfully load the /etc/samba/smb.conf file. Note that testparm cannot verify that the configured services will be available or work as expected.

Important

Red Hat recommends that you verify the /etc/samba/smb.conf file by using testparm after each modification of this file.

Prerequisites

  • You installed Samba.
  • The /etc/samba/smb.conf file exits.

Procedure

  1. Run the testparm utility as the root user: 

    # testparm
Load smb config files from /etc/samba/smb.conf
rlimit_max: increasing rlimit_max (1024) to minimum Windows limit (16384)
Unknown parameter encountered: "log levell"
Processing section "[example_share]"
Loaded services file OK.
ERROR: The idmap range for the domain * (tdb) overlaps with the range of DOMAIN (ad)!

Server role: ROLE_DOMAIN_MEMBER

Press enter to see a dump of your service definitions

# Global parameters
[global]
	...

[example_share]
	...

    The previous example output reports a non-existent parameter and an incorrect ID mapping configuration.

  2. If testparm reports incorrect parameters, values, or other errors in the configuration, fix the problem and run the utility again.

3.3. Setting up Samba as a standalone server

You can set up Samba as a server that is not a member of a domain. In this installation mode, Samba authenticates users to a local database instead of to a central DC. Additionally, you can enable guest access to allow users to connect to one or multiple services without authentication.

3.3.1. Setting up the server configuration for the standalone server

You can set up the server configuration for a Samba standalone server.

Procedure

  1. Install the samba package: 

    # yum install samba

  2. Edit the /etc/samba/smb.conf file and set the following parameters: 

    [global]
	workgroup = Example-WG
	netbios name = Server
	security = user

	log file = /var/log/samba/%m.log
	log level = 1

    This configuration defines a standalone server named Server within the Example-WG work group. Additionally, this configuration enables logging on a minimal level (1) and log files will be stored in the /var/log/samba/ directory. Samba will expand the %m macro in the log file parameter to the NetBIOS name of connecting clients. This enables individual log files for each client.

  3. Optionally, configure file or printer sharing. See:

  4. Verify the /etc/samba/smb.conf file: 

    # testparm

  5. If you set up shares that require authentication, create the user accounts.

    For details, see Creating and enabling local user accounts.

  6. Open the required ports and reload the firewall configuration by using the firewall-cmd utility: 

    # firewall-cmd --permanent --add-service=samba
# firewall-cmd --reload

  7. Enable and start the smb service: 

    # systemctl enable --now smb

Additional resources

  • smb.conf(5) man page

3.3.2. Creating and enabling local user accounts

To enable users to authenticate when they connect to a share, you must create the accounts on the Samba host both in the operating system and in the Samba database. Samba requires the operating system account to validate the Access Control Lists (ACL) on file system objects and the Samba account to authenticate connecting users.

If you use the passdb backend = tdbsam default setting, Samba stores user accounts in the /var/lib/samba/private/passdb.tdb database.

You can create a local Samba user named example.

Prerequisites

  • Samba is installed and configured as a standalone server.

Procedure

  1. Create the operating system account: 

    # useradd -M -s /sbin/nologin example

    This command adds the example account without creating a home directory. If the account is only used to authenticate to Samba, assign the /sbin/nologin command as shell to prevent the account from logging in locally.

  2. Set a password to the operating system account to enable it: 

    # passwd example
Enter new UNIX password: password
Retype new UNIX password: password
passwd: password updated successfully

    Samba does not use the password set on the operating system account to authenticate. However, you need to set a password to enable the account. If an account is disabled, Samba denies access if this user connects.

  3. Add the user to the Samba database and set a password to the account: 

    # smbpasswd -a example
New SMB password: password
Retype new SMB password: password
Added user example.

    Use this password to authenticate when using this account to connect to a Samba share.

  4. Enable the Samba account: 

    # smbpasswd -e example
Enabled user example.

3.4. Understanding and configuring Samba ID mapping

Windows domains distinguish users and groups by unique Security Identifiers (SID). However, Linux requires unique UIDs and GIDs for each user and group. If you run Samba as a domain member, the winbindd service is responsible for providing information about domain users and groups to the operating system.

To enable the winbindd service to provide unique IDs for users and groups to Linux, you must configure ID mapping in the /etc/samba/smb.conf file for:

  • The local database (default domain)
  • The AD or NT4 domain the Samba server is a member of
  • Each trusted domain from which users must be able to access resources on this Samba server

Samba provides different ID mapping back ends for specific configurations. The most frequently used back ends are:

Back endUse case

tdb

The * default domain only

ad

AD domains only

rid

AD and NT4 domains

autorid

AD, NT4, and the * default domain

3.4.1. Planning Samba ID ranges

Regardless of whether you store the Linux UIDs and GIDs in AD or if you configure Samba to generate them, each domain configuration requires a unique ID range that must not overlap with any of the other domains.

Warning

If you set overlapping ID ranges, Samba fails to work correctly.

Example 3.1. Unique ID Ranges

The following shows non-overlapping ID mapping ranges for the default (*), AD-DOM, and the TRUST-DOM domains. 

[global]
...
idmap config * : backend = tdb
idmap config * : range = 10000-999999

idmap config AD-DOM:backend = rid
idmap config AD-DOM:range = 2000000-2999999

idmap config TRUST-DOM:backend = rid
idmap config TRUST-DOM:range = 4000000-4999999
Important

You can only assign one range per domain. Therefore, leave enough space between the domains ranges. This enables you to extend the range later if your domain grows.

If you later assign a different range to a domain, the ownership of files and directories previously created by these users and groups will be lost.

3.4.2. The * default domain

In a domain environment, you add one ID mapping configuration for each of the following:

  • The domain the Samba server is a member of
  • Each trusted domain that should be able to access the Samba server

However, for all other objects, Samba assigns IDs from the default domain. This includes:

  • Local Samba users and groups
  • Samba built-in accounts and groups, such as BUILTIN\Administrators
Important

You must configure the default domain as described in this section to enable Samba to operate correctly.

The default domain back end must be writable to permanently store the assigned IDs.

For the default domain, you can use one of the following back ends:

tdb

When you configure the default domain to use the tdb back end, set an ID range that is big enough to include objects that will be created in the future and that are not part of a defined domain ID mapping configuration.

For example, set the following in the [global] section in the /etc/samba/smb.conf file: 

idmap config * : backend = tdb
idmap config * : range = 10000-999999

For further details, see Using the TDB ID mapping back end.

autorid

When you configure the default domain to use the autorid back end, adding additional ID mapping configurations for domains is optional.

For example, set the following in the [global] section in the /etc/samba/smb.conf file: 

idmap config * : backend = autorid
idmap config * : range = 10000-999999

For further details, see Using the autorid ID mapping back end.

3.4.3. Using the tdb ID mapping back end

The winbindd service uses the writable tdb ID mapping back end by default to store Security Identifier (SID), UID, and GID mapping tables. This includes local users, groups, and built-in principals.

Use this back end only for the * default domain. For example: 

idmap config * : backend = tdb
idmap config * : range = 10000-999999

Additional resources

3.4.4. Using the ad ID mapping back end

You can configure a Samba AD member to use the ad ID mapping back end.

The ad ID mapping back end implements a read-only API to read account and group information from AD. This provides the following benefits:

  • All user and group settings are stored centrally in AD.
  • User and group IDs are consistent on all Samba servers that use this back end.
  • The IDs are not stored in a local database which can corrupt, and therefore file ownerships cannot be lost.
Note

The ad ID mapping back end does not support Active Directory domains with one-way trusts. If you configure a domain member in an Active Directory with one-way trusts, use instead one of the following ID mapping back ends: tdb, rid, or autorid.

The ad back end reads the following attributes from AD:

AD attribute nameObject typeMapped to

sAMAccountName

User and group

User or group name, depending on the object

uidNumber

User

User ID (UID)

gidNumber

Group

Group ID (GID)

loginShell [a]

User

Path to the shell of the user

unixHomeDirectory [a]

User

Path to the home directory of the user

primaryGroupID [b]

User

Primary group ID

[a] Samba only reads this attribute if you set idmap config DOMAIN:unix_nss_info = yes.
[b] Samba only reads this attribute if you set idmap config DOMAIN:unix_primary_group = yes.

Prerequisites

  • Both users and groups must have unique IDs set in AD, and the IDs must be within the range configured in the /etc/samba/smb.conf file. Objects whose IDs are outside of the range will not be available on the Samba server.
  • Users and groups must have all required attributes set in AD. If required attributes are missing, the user or group will not be available on the Samba server. The required attributes depend on your configuration. .Prerequisites
  • You installed Samba.
  • The Samba configuration, except ID mapping, exists in the /etc/samba/smb.conf file.

Procedure

  1. Edit the [global] section in the /etc/samba/smb.conf file:

    1. Add an ID mapping configuration for the default domain (*) if it does not exist. For example: 

      idmap config * : backend = tdb
idmap config * : range = 10000-999999

    2. Enable the ad ID mapping back end for the AD domain: 

      idmap config DOMAIN : backend = ad

    3. Set the range of IDs that is assigned to users and groups in the AD domain. For example: 

      idmap config DOMAIN : range = 2000000-2999999
      Important

      The range must not overlap with any other domain configuration on this server. Additionally, the range must be set big enough to include all IDs assigned in the future. For further details, see Planning Samba ID ranges.

    4. Set that Samba uses the RFC 2307 schema when reading attributes from AD: 

      idmap config DOMAIN : schema_mode = rfc2307

    5. To enable Samba to read the login shell and the path to the users home directory from the corresponding AD attribute, set: 

      idmap config DOMAIN : unix_nss_info = yes

      Alternatively, you can set a uniform domain-wide home directory path and login shell that is applied to all users. For example: 

      template shell = /bin/bash
template homedir = /home/%U

    6. By default, Samba uses the primaryGroupID attribute of a user object as the user’s primary group on Linux. Alternatively, you can configure Samba to use the value set in the gidNumber attribute instead: 

      idmap config DOMAIN : unix_primary_group = yes

  2. Verify the /etc/samba/smb.conf file: 

    # testparm

  3. Reload the Samba configuration: 

    # smbcontrol all reload-config

Additional resources

  • The * default domain
  • smb.conf(5) and idmap_ad(8) man pages
  • VARIABLE SUBSTITUTIONS section in the smb.conf(5) man page

3.4.5. Using the rid ID mapping back end

You can configure a Samba domain member to use the rid ID mapping back end.

Samba can use the relative identifier (RID) of a Windows SID to generate an ID on Red Hat Enterprise Linux.

Note

The RID is the last part of a SID. For example, if the SID of a user is S-1-5-21-5421822485-1151247151-421485315-30014, then 30014 is the corresponding RID.

The rid ID mapping back end implements a read-only API to calculate account and group information based on an algorithmic mapping scheme for AD and NT4 domains. When you configure the back end, you must set the lowest and highest RID in the idmap config DOMAIN : range parameter. Samba will not map users or groups with a lower or higher RID than set in this parameter.

Important

As a read-only back end, rid cannot assign new IDs, such as for BUILTIN groups. Therefore, do not use this back end for the * default domain.

Benefits of using the rid back end

  • All domain users and groups that have an RID within the configured range are automatically available on the domain member.
  • You do not need to manually assign IDs, home directories, and login shells.

Drawbacks of using the rid back end

  • All domain users get the same login shell and home directory assigned. However, you can use variables.
  • User and group IDs are only the same across Samba domain members if all use the rid back end with the same ID range settings.
  • You cannot exclude individual users or groups from being available on the domain member. Only users and groups outside of the configured range are excluded.
  • Based on the formulas the winbindd service uses to calculate the IDs, duplicate IDs can occur in multi-domain environments if objects in different domains have the same RID.

Prerequisites

  • You installed Samba.
  • The Samba configuration, except ID mapping, exists in the /etc/samba/smb.conf file.

Procedure

  1. Edit the [global] section in the /etc/samba/smb.conf file:

    1. Add an ID mapping configuration for the default domain (*) if it does not exist. For example: 

      idmap config * : backend = tdb
idmap config * : range = 10000-999999

    2. Enable the rid ID mapping back end for the domain: 

      idmap config DOMAIN : backend = rid

    3. Set a range that is big enough to include all RIDs that will be assigned in the future. For example: 

      idmap config DOMAIN : range = 2000000-2999999

      Samba ignores users and groups whose RIDs in this domain are not within the range.

      Important

      The range must not overlap with any other domain configuration on this server. Additionally, the range must be set big enough to include all IDs assigned in the future. For further details, see Planning Samba ID ranges.

    4. Set a shell and home directory path that will be assigned to all mapped users. For example: 

      template shell = /bin/bash
template homedir = /home/%U

  2. Verify the /etc/samba/smb.conf file: 

    # testparm

  3. Reload the Samba configuration: 

    # smbcontrol all reload-config

Additional resources

  • The * default domain
  • VARIABLE SUBSTITUTIONS section in the smb.conf(5) man page
  • Calculation of the local ID from a RID, see the idmap_rid(8) man page

3.4.6. Using the autorid ID mapping back end

You can configure a Samba domain member to use the autorid ID mapping back end.

The autorid back end works similar to the rid ID mapping back end, but can automatically assign IDs for different domains. This enables you to use the autorid back end in the following situations:

  • Only for the * default domain
  • For the * default domain and additional domains, without the need to create ID mapping configurations for each of the additional domains
  • Only for specific domains
Note

If you use autorid for the default domain, adding additional ID mapping configuration for domains is optional.

Parts of this section were adopted from the idmap config autorid documentation published in the Samba Wiki. License: CC BY 4.0. Authors and contributors: See the history tab on the Wiki page.

Benefits of using the autorid back end

  • All domain users and groups whose calculated UID and GID is within the configured range are automatically available on the domain member.
  • You do not need to manually assign IDs, home directories, and login shells.
  • No duplicate IDs, even if multiple objects in a multi-domain environment have the same RID.

Drawbacks

  • User and group IDs are not the same across Samba domain members.
  • All domain users get the same login shell and home directory assigned. However, you can use variables.
  • You cannot exclude individual users or groups from being available on the domain member. Only users and groups whose calculated UID or GID is outside of the configured range are excluded.

Prerequisites

  • You installed Samba.
  • The Samba configuration, except ID mapping, exists in the /etc/samba/smb.conf file.

Procedure

  1. Edit the [global] section in the /etc/samba/smb.conf file:

    1. Enable the autorid ID mapping back end for the * default domain: 

      idmap config * : backend = autorid

    2. Set a range that is big enough to assign IDs for all existing and future objects. For example: 

      idmap config * : range = 10000-999999

      Samba ignores users and groups whose calculated IDs in this domain are not within the range.

      Warning

      After you set the range and Samba starts using it, you can only increase the upper limit of the range. Any other change to the range can result in new ID assignments, and thus in losing file ownerships.

    3. Optionally, set a range size. For example: 

      idmap config * : rangesize = 200000

      Samba assigns this number of continuous IDs for each domain’s object until all IDs from the range set in the idmap config * : range parameter are taken.

      Note

      If you set a rangesize, you need to adapt the range accordingly. The range needs to be a multiple of the rangesize.

    4. Set a shell and home directory path that will be assigned to all mapped users. For example: 

      template shell = /bin/bash
template homedir = /home/%U

    5. Optionally, add additional ID mapping configuration for domains. If no configuration for an individual domain is available, Samba calculates the ID using the autorid back end settings in the previously configured * default domain.

      Important

      The range must not overlap with any other domain configuration on this server. Additionally, the range must be set big enough to include all IDs assigned in the future. For further details, see Planning Samba ID ranges.

  2. Verify the /etc/samba/smb.conf file: 

    # testparm

  3. Reload the Samba configuration: 

    # smbcontrol all reload-config

Additional resources

  • THE MAPPING FORMULAS section in the idmap_autorid(8) man page
  • rangesize parameter description in the idmap_autorid(8) man page
  • VARIABLE SUBSTITUTIONS section in the smb.conf(5) man page

3.5. Setting up Samba as an AD domain member server

If you are running an AD or NT4 domain, use Samba to add your Red Hat Enterprise Linux server as a member to the domain to gain the following:

  • Access domain resources on other domain members
  • Authenticate domain users to local services, such as sshd
  • Share directories and printers hosted on the server to act as a file and print server

3.5.1. Joining a RHEL system to an AD domain

Samba Winbind is an alternative to the System Security Services Daemon (SSSD) for connecting a Red Hat Enterprise Linux (RHEL) system with Active Directory (AD). You can join a RHEL system to an AD domain by using realmd to configure Samba Winbind.

Procedure

  1. If your AD requires the deprecated RC4 encryption type for Kerberos authentication, enable support for these ciphers in RHEL: 

    # update-crypto-policies --set DEFAULT:AD-SUPPORT

  2. Install the following packages: 

    # yum install realmd oddjob-mkhomedir oddjob samba-winbind-clients \
       samba-winbind samba-common-tools samba-winbind-krb5-locator

  3. To share directories or printers on the domain member, install the samba package: 

    # yum install samba

  4. Backup the existing /etc/samba/smb.conf Samba configuration file: 

    # mv /etc/samba/smb.conf /etc/samba/smb.conf.bak

  5. Join the domain. For example, to join a domain named ad.example.com: 

    # realm join --membership-software=samba --client-software=winbind ad.example.com

    Using the previous command, the realm utility automatically:

    • Creates a /etc/samba/smb.conf file for a membership in the ad.example.com domain
    • Adds the winbind module for user and group lookups to the /etc/nsswitch.conf file
    • Updates the Pluggable Authentication Module (PAM) configuration files in the /etc/pam.d/ directory
    • Starts the winbind service and enables the service to start when the system boots
  6. Optionally, set an alternative ID mapping back end or customized ID mapping settings in the /etc/samba/smb.conf file. For details, see Understanding and configuring Samba ID mapping.

  7. Verify that the winbind service is running: 

    # systemctl status winbind
...
   Active: active (running) since Tue 2018-11-06 19:10:40 CET; 15s ago
    Important

    To enable Samba to query domain user and group information, the winbind service must be running before you start smb.

  8. If you installed the samba package to share directories and printers, enable and start the smb service: 

    # systemctl enable --now smb
  9. Optionally, if you are authenticating local logins to Active Directory, enable the winbind_krb5_localauth plug-in. See Using the local authorization plug-in for MIT Kerberos.

Verification steps

  1. Display an AD user’s details, such as the AD administrator account in the AD domain: 

    # getent passwd "AD\administrator"
AD\administrator:*:10000:10000::/home/administrator@AD:/bin/bash

  2. Query the members of the domain users group in the AD domain: 

    # getent group "AD\Domain Users"
    AD\domain users:x:10000:user1,user2

  3. Optionally, verify that you can use domain users and groups when you set permissions on files and directories. For example, to set the owner of the /srv/samba/example.txt file to AD\administrator and the group to AD\Domain Users: 

    # chown "AD\administrator":"AD\Domain Users" /srv/samba/example.txt

  4. Verify that Kerberos authentication works as expected:

    1. On the AD domain member, obtain a ticket for the administrator@AD.EXAMPLE.COM principal: 

      # kinit administrator@AD.EXAMPLE.COM

    2. Display the cached Kerberos ticket: 

      # klist
Ticket cache: KCM:0
Default principal: administrator@AD.EXAMPLE.COM

Valid starting       Expires              Service principal
01.11.2018 10:00:00  01.11.2018 20:00:00  krbtgt/AD.EXAMPLE.COM@AD.EXAMPLE.COM
        renew until 08.11.2018 05:00:00

  5. Display the available domains: 

    # wbinfo --all-domains
BUILTIN
SAMBA-SERVER
AD

Additional resources

3.5.2. Using the local authorization plug-in for MIT Kerberos

The winbind service provides Active Directory users to the domain member. In certain situations, administrators want to enable domain users to authenticate to local services, such as an SSH server, which are running on the domain member. When using Kerberos to authenticate the domain users, enable the winbind_krb5_localauth plug-in to correctly map Kerberos principals to Active Directory accounts through the winbind service.

For example, if the sAMAccountName attribute of an Active Directory user is set to EXAMPLE and the user tries to log with the user name lowercase, Kerberos returns the user name in upper case. As a consequence, the entries do not match and authentication fails.

Using the winbind_krb5_localauth plug-in, the account names are mapped correctly. Note that this only applies to GSSAPI authentication and not for getting the initial ticket granting ticket (TGT).

Prerequisites

  • Samba is configured as a member of an Active Directory.
  • Red Hat Enterprise Linux authenticates log in attempts against Active Directory.
  • The winbind service is running.

Procedure

Edit the /etc/krb5.conf file and add the following section: 

[plugins]
localauth = {
     module = winbind:/usr/lib64/samba/krb5/winbind_krb5_localauth.so
     enable_only = winbind
}

Additional resources

  • winbind_krb5_localauth(8) man page.

3.6. Setting up Samba on an IdM domain member

You can set up Samba on a host that is joined to a Red Hat Identity Management (IdM) domain. Users from IdM and also, if available, from trusted Active Directory (AD) domains, can access shares and printer services provided by Samba.

Important

Using Samba on an IdM domain member is an unsupported Technology Preview feature and contains certain limitations. For example, IdM trust controllers do not support the Active Directory Global Catalog service, and they do not support resolving IdM groups using the Distributed Computing Environment / Remote Procedure Calls (DCE/RPC) protocols. As a consequence, AD users can only access Samba shares and printers hosted on IdM clients when logged in to other IdM clients; AD users logged into a Windows machine can not access Samba shares hosted on an IdM domain member.

Customers deploying Samba on IdM domain members are encouraged to provide feedback to Red Hat.

Prerequisites

  • The host is joined as a client to the IdM domain.
  • Both the IdM servers and the client must run on RHEL 8.1 or later.

3.6.1. Preparing the IdM domain for installing Samba on domain members

Before you can set up Samba on an IdM client, you must prepare the IdM domain using the ipa-adtrust-install utility on an IdM server.

Note

Any system where you run the ipa-adtrust-install command automatically becomes an AD trust controller. However, you must run ipa-adtrust-install only once on an IdM server.

Prerequisites

  • IdM server is installed.
  • You need root privileges to install packages and restart IdM services.

Procedure

  1. Install the required packages: 

    [root@ipaserver ~]# yum install ipa-server-trust-ad samba-client

  2. Authenticate as the IdM administrative user: 

    [root@ipaserver ~]# kinit admin

  3. Run the ipa-adtrust-install utility: 

    [root@ipaserver ~]# ipa-adtrust-install

    The DNS service records are created automatically if IdM was installed with an integrated DNS server.

    If you installed IdM without an integrated DNS server, ipa-adtrust-install prints a list of service records that you must manually add to DNS before you can continue.

  4. The script prompts you that the /etc/samba/smb.conf already exists and will be rewritten: 

    WARNING: The smb.conf already exists. Running ipa-adtrust-install will break your existing Samba configuration.

Do you wish to continue? [no]: yes

  5. The script prompts you to configure the slapi-nis plug-in, a compatibility plug-in that allows older Linux clients to work with trusted users: 

    Do you want to enable support for trusted domains in Schema Compatibility plugin?
This will allow clients older than SSSD 1.9 and non-Linux clients to work with trusted users.

Enable trusted domains support in slapi-nis? [no]: yes

  6. When prompted, enter the NetBIOS name for the IdM domain or press Enter to accept the name suggested: 

    Trust is configured but no NetBIOS domain name found, setting it now.
Enter the NetBIOS name for the IPA domain.
Only up to 15 uppercase ASCII letters, digits and dashes are allowed.
Example: EXAMPLE.

NetBIOS domain name [IDM]:

  7. You are prompted to run the SID generation task to create a SID for any existing users: 

    Do you want to run the ipa-sidgen task? [no]: yes

    This is a resource-intensive task, so if you have a high number of users, you can run this at another time.

  8. (Optional) By default, the Dynamic RPC port range is defined as 49152-65535 for Windows Server 2008 and later. If you need to define a different Dynamic RPC port range for your environment, configure Samba to use different ports and open those ports in your firewall settings. The following example sets the port range to 55000-65000. 

    [root@ipaserver ~]# net conf setparm global 'rpc server dynamic port range' 55000-65000
[root@ipaserver ~]# firewall-cmd --add-port=55000-65000/tcp
[root@ipaserver ~]# firewall-cmd --runtime-to-permanent

  9. Restart the ipa service: 

    [root@ipaserver ~]# ipactl restart

  10. Use the smbclient utility to verify that Samba responds to Kerberos authentication from the IdM side: 

    [root@ipaserver ~]# smbclient -L server.idm.example.com -U user_name --use-kerberos=required
lp_load_ex: changing to config backend registry
    Sharename       Type      Comment
    ---------       ----      -------
    IPC$            IPC       IPC Service (Samba 4.15.2)
...

3.6.2. Enabling the AES encryption type in Active Directory using a GPO

This section describes how to enable the AES encryption type in Active Directory (AD) using a group policy object (GPO). Certain features on RHEL, such as running a Samba server on an IdM client, require this encryption type.

Note that RHEL no longer supports the weak DES and RC4 encryption types.

Prerequisites

  • You are logged into AD as a user who can edit group policies.
  • The Group Policy Management Console is installed on the computer.

Procedure

  1. Open the Group Policy Management Console.
  2. Right-click Default Domain Policy, and select Edit. The Group Policy Management Editor opens.
  3. Navigate to Computer Configuration → Policies → Windows Settings → Security Settings → Local Policies → Security Options.
  4. Double-click the Network security: Configure encryption types allowed for Kerberos policy.
  5. Select AES256_HMAC_SHA1 and, optionally, Future encryption types.
  6. Click OK.
  7. Close the Group Policy Management Editor.
  8. Repeat the steps for the Default Domain Controller Policy.

  9. Wait until the Windows domain controllers (DC) applied the group policy automatically. Alternatively, to apply the GPO manually on a DC, enter the following command using an account that has administrator permissions: 

    C:\> gpupdate /force /target:computer

3.6.3. Installing and configuring a Samba server on an IdM client

You can install and configure Samba on a client enrolled in an IdM domain.

Prerequisites

Procedure

  1. Install the ipa-client-samba package: 

    [root@idm_client]# yum install ipa-client-samba

  2. Use the ipa-client-samba utility to prepare the client and create an initial Samba configuration: 

    [root@idm_client]# ipa-client-samba
Searching for IPA server...
IPA server: DNS discovery
Chosen IPA master: idm_server.idm.example.com
SMB principal to be created: cifs/idm_client.idm.example.com@IDM.EXAMPLE.COM
NetBIOS name to be used: IDM_CLIENT
Discovered domains to use:

 Domain name: idm.example.com
NetBIOS name: IDM
         SID: S-1-5-21-525930803-952335037-206501584
    ID range: 212000000 - 212199999

 Domain name: ad.example.com
NetBIOS name: AD
         SID: None
    ID range: 1918400000 - 1918599999

Continue to configure the system with these values? [no]: yes
Samba domain member is configured. Please check configuration at /etc/samba/smb.conf and start smb and winbind services

  3. By default, ipa-client-samba automatically adds the [homes] section to the /etc/samba/smb.conf file that dynamically shares a user’s home directory when the user connects. If users do not have home directories on this server, or if you do not want to share them, remove the following lines from /etc/samba/smb.conf: 

    [homes]
    read only = no

  4. Share directories and printers. For details, see:

  5. Open the ports required for a Samba client in the local firewall: 

    [root@idm_client]# firewall-cmd --permanent --add-service=samba-client
[root@idm_client]# firewall-cmd --reload

  6. Enable and start the smb and winbind services: 

    [root@idm_client]# systemctl enable --now smb winbind

Verification steps

Run the following verification step on a different IdM domain member that has the samba-client package installed:

  • List the shares on the Samba server using Kerberos authentication: 

    $ smbclient -L idm_client.idm.example.com -U user_name --use-kerberos=required
lp_load_ex: changing to config backend registry

    Sharename       Type      Comment
    ---------       ----      -------
    example         Disk
    IPC$            IPC       IPC Service (Samba 4.15.2)
...

Additional resources

  • ipa-client-samba(1) man page

3.6.4. Manually adding an ID mapping configuration if IdM trusts a new domain

Samba requires an ID mapping configuration for each domain from which users access resources. On an existing Samba server running on an IdM client, you must manually add an ID mapping configuration after the administrator added a new trust to an Active Directory (AD) domain.

Prerequisites

  • You configured Samba on an IdM client. Afterward, a new trust was added to IdM.
  • The DES and RC4 encryption types for Kerberos must be disabled in the trusted AD domain. For security reasons, RHEL 8 does not support these weak encryption types.

Procedure

  1. Authenticate using the host’s keytab: 

    [root@idm_client]# kinit -k

  2. Use the ipa idrange-find command to display both the base ID and the ID range size of the new domain. For example, the following command displays the values for the ad.example.com domain: 

    [root@idm_client]# ipa idrange-find --name="AD.EXAMPLE.COM_id_range" --raw
---------------
1 range matched
---------------
  cn: AD.EXAMPLE.COM_id_range
  ipabaseid: 1918400000
  ipaidrangesize: 200000
  ipabaserid: 0
  ipanttrusteddomainsid: S-1-5-21-968346183-862388825-1738313271
  iparangetype: ipa-ad-trust
----------------------------
Number of entries returned 1
----------------------------

    You need the values from the ipabaseid and ipaidrangesize attributes in the next steps.

  3. To calculate the highest usable ID, use the following formula: 

    maximum_range = ipabaseid + ipaidrangesize - 1

    With the values from the previous step, the highest usable ID for the ad.example.com domain is 1918599999 (1918400000 + 200000 - 1).

  4. Edit the /etc/samba/smb.conf file, and add the ID mapping configuration for the domain to the [global] section: 

    idmap config AD : range = 1918400000 - 1918599999
idmap config AD : backend = sss

    Specify the value from ipabaseid attribute as the lowest and the computed value from the previous step as the highest value of the range.

  5. Restart the smb and winbind services: 

    [root@idm_client]# systemctl restart smb winbind

Verification steps

  • List the shares on the Samba server using Kerberos authentication: 

    $ smbclient -L idm_client.idm.example.com -U user_name --use-kerberos=required
lp_load_ex: changing to config backend registry

    Sharename       Type      Comment
    ---------       ----      -------
    example         Disk
    IPC$            IPC       IPC Service (Samba 4.15.2)
...

3.6.5. Additional resources

3.7. Setting up a Samba file share that uses POSIX ACLs

As a Linux service, Samba supports shares with POSIX ACLs. They enable you to manage permissions locally on the Samba server using utilities, such as chmod. If the share is stored on a file system that supports extended attributes, you can define ACLs with multiple users and groups.

Note

If you need to use fine-granular Windows ACLs instead, see Setting up a share that uses Windows ACLs.

Parts of this section were adopted from the Setting up a Share Using POSIX ACLs documentation published in the Samba Wiki. License: CC BY 4.0. Authors and contributors: See the history tab on the Wiki page.

3.7.1. Adding a share that uses POSIX ACLs

You can create a share named example that provides the content of the /srv/samba/example/ directory, and uses POSIX ACLs.

Prerequisites

Samba has been set up in one of the following modes:

Procedure

  1. Create the folder if it does not exist. For example: 

    # mkdir -p /srv/samba/example/

  2. If you run SELinux in enforcing mode, set the samba_share_t context on the directory: 

    # semanage fcontext -a -t samba_share_t "/srv/samba/example(/.*)?"
# restorecon -Rv /srv/samba/example/

  3. Set file system ACLs on the directory. For details, see:

  4. Add the example share to the /etc/samba/smb.conf file. For example, to add the share write-enabled: 

    [example]
	path = /srv/samba/example/
	read only = no
    Note

    Regardless of the file system ACLs; if you do not set read only = no, Samba shares the directory in read-only mode.

  5. Verify the /etc/samba/smb.conf file: 

    # testparm

  6. Open the required ports and reload the firewall configuration using the firewall-cmd utility: 

    # firewall-cmd --permanent --add-service=samba
# firewall-cmd --reload

  7. Restart the smb service: 

    # systemctl restart smb

3.7.2. Setting standard Linux ACLs on a Samba share that uses POSIX ACLs

The standard ACLs on Linux support setting permissions for one owner, one group, and for all other undefined users. You can use the chown, chgrp, and chmod utility to update the ACLs. If you require precise control, then you use the more complex POSIX ACLs, see

Setting extended ACLs on a Samba share that uses POSIX ACLs.

The following procedure sets the owner of the /srv/samba/example/ directory to the root user, grants read and write permissions to the Domain Users group, and denies access to all other users.

Prerequisites

  • The Samba share on which you want to set the ACLs exists.

Procedure

# chown root:"Domain Users" /srv/samba/example/
# chmod 2770 /srv/samba/example/

Note

Enabling the set-group-ID (SGID) bit on a directory automatically sets the default group for all new files and subdirectories to that of the directory group, instead of the usual behavior of setting it to the primary group of the user who created the new directory entry.

Additional resources

  • chown(1) and chmod(1) man pages

3.7.3. Setting extended ACLs on a Samba share that uses POSIX ACLs

If the file system the shared directory is stored on supports extended ACLs, you can use them to set complex permissions. Extended ACLs can contain permissions for multiple users and groups.

Extended POSIX ACLs enable you to configure complex ACLs with multiple users and groups. However, you can only set the following permissions:

  • No access
  • Read access
  • Write access
  • Full control

If you require the fine-granular Windows permissions, such as Create folder / append data, configure the share to use Windows ACLs. See Setting up a share that uses Windows ACLs.

The following procedure shows how to enable extended ACLs on a share. Additionally, it contains an example about setting extended ACLs.

Prerequisites

  • The Samba share on which you want to set the ACLs exists.

Procedure

  1. Enable the following parameter in the share’s section in the /etc/samba/smb.conf file to enable ACL inheritance of extended ACLs: 

    inherit acls = yes

    For details, see the parameter description in the smb.conf(5) man page.

  2. Restart the smb service: 

    # systemctl restart smb

  3. Set the ACLs on the directory. For example:

    Example 3.2. Setting Extended ACLs

    The following procedure sets read, write, and execute permissions for the Domain Admins group, read, and execute permissions for the Domain Users group, and deny access to everyone else on the /srv/samba/example/ directory:

    1. Disable auto-granting permissions to the primary group of user accounts: 

      # setfacl -m group::--- /srv/samba/example/
# setfacl -m default:group::--- /srv/samba/example/

      The primary group of the directory is additionally mapped to the dynamic CREATOR GROUP principal. When you use extended POSIX ACLs on a Samba share, this principal is automatically added and you cannot remove it.

    2. Set the permissions on the directory:

      1. Grant read, write, and execute permissions to the Domain Admins group: 

        # setfacl -m group:"DOMAIN\Domain Admins":rwx /srv/samba/example/

      2. Grant read and execute permissions to the Domain Users group: 

        # setfacl -m group:"DOMAIN\Domain Users":r-x /srv/samba/example/

      3. Set permissions for the other ACL entry to deny access to users that do not match the other ACL entries: 

        # setfacl -R -m other::--- /srv/samba/example/

      These settings apply only to this directory. In Windows, these ACLs are mapped to the This folder only mode.

    3. To enable the permissions set in the previous step to be inherited by new file system objects created in this directory: 

      # setfacl -m default:group:"DOMAIN\Domain Admins":rwx /srv/samba/example/
# setfacl -m default:group:"DOMAIN\Domain Users":r-x /srv/samba/example/
# setfacl -m default:other::--- /srv/samba/example/

      With these settings, the This folder only mode for the principals is now set to This folder, subfolders, and files.

    Samba maps the permissions set in the procedure to the following Windows ACLs:

    PrincipalAccessApplies to

    Domain\Domain Admins

    Full control

    This folder, subfolders, and files

    Domain\Domain Users

    Read & execute

    This folder, subfolders, and files

    Everyone [a]

    None

    This folder, subfolders, and files

    owner (Unix User\owner) [b]

    Full control

    This folder only

    primary_group (Unix User\primary_group) [c]

    None

    This folder only

    CREATOR OWNER [d] [e]

    Full control

    Subfolders and files only

    CREATOR GROUP [e] [f]

    None

    Subfolders and files only

    [a] Samba maps the permissions for this principal from the other ACL entry.
    [b] Samba maps the owner of the directory to this entry.
    [c] Samba maps the primary group of the directory to this entry.
    [d] On new file system objects, the creator inherits automatically the permissions of this principal.
    [e] Configuring or removing these principals from the ACLs not supported on shares that use POSIX ACLs.
    [f] On new file system objects, the creator’s primary group inherits automatically the permissions of this principal.

3.8. Setting permissions on a share that uses POSIX ACLs

Optionally, to limit or grant access to a Samba share, you can set certain parameters in the share’s section in the /etc/samba/smb.conf file.

Note

Share-based permissions manage if a user, group, or host is able to access a share. These settings do not affect file system ACLs.

Use share-based settings to restrict access to shares, for example, to deny access from specific hosts.

Prerequisites

  • A share with POSIX ACLs has been set up.

3.8.1. Configuring user and group-based share access

User and group-based access control enables you to grant or deny access to a share for certain users and groups.

Prerequisites

  • The Samba share on which you want to set user or group-based access exists.

Procedure

  1. For example, to enable all members of the Domain Users group to access a share while access is denied for the user account, add the following parameters to the share’s configuration: 

    valid users = +DOMAIN\"Domain Users"
invalid users = DOMAIN\user

    The invalid users parameter has a higher priority than the valid users parameter. For example, if the user account is a member of the Domain Users group, access is denied to this account when you use the previous example.

  2. Reload the Samba configuration: 

    # smbcontrol all reload-config

Additional resources

  • smb.conf(5) man page

3.8.2. Configuring host-based share access

Host-based access control enables you to grant or deny access to a share based on client’s host names, IP addresses, or IP range.

The following procedure explains how to enable the 127.0.0.1 IP address, the 192.0.2.0/24 IP range, and the client1.example.com host to access a share, and additionally deny access for the client2.example.com host:

Prerequisites

  • The Samba share on which you want to set host-based access exists.

Procedure

  1. Add the following parameters to the configuration of the share in the /etc/samba/smb.conf file: 

    hosts allow = 127.0.0.1 192.0.2.0/24 client1.example.com
hosts deny = client2.example.com

    The hosts deny parameter has a higher priority than hosts allow. For example, if client1.example.com resolves to an IP address that is listed in the hosts allow parameter, access for this host is denied.

  2. Reload the Samba configuration: 

    # smbcontrol all reload-config

Additional resources

  • smb.conf(5) man page

3.9. Setting up a share that uses Windows ACLs

Samba supports setting Windows ACLs on shares and file system object. This enables you to:

  • Use the fine-granular Windows ACLs
  • Manage share permissions and file system ACLs using Windows

Alternatively, you can configure a share to use POSIX ACLs. For details, see Setting up a Samba file share that uses POSIX ACLs.

Parts of this section were adopted from the Setting up a Share Using Windows ACLs documentation published in the Samba Wiki. License: CC BY 4.0. Authors and contributors: See the history tab on the Wiki page.

3.9.1. Granting the SeDiskOperatorPrivilege privilege

Only users and groups having the SeDiskOperatorPrivilege privilege granted can configure permissions on shares that use Windows ACLs.

Procedure

  1. For example, to grant the SeDiskOperatorPrivilege privilege to the DOMAIN\Domain Admins group: 

    # net rpc rights grant "DOMAIN\Domain Admins" SeDiskOperatorPrivilege -U "DOMAIN\administrator"
Enter DOMAIN\administrator's password:
Successfully granted rights.
    Note

    In a domain environment, grant SeDiskOperatorPrivilege to a domain group. This enables you to centrally manage the privilege by updating a user’s group membership.

  2. To list all users and groups having SeDiskOperatorPrivilege granted: 

    # net rpc rights list privileges SeDiskOperatorPrivilege -U "DOMAIN\administrator"
Enter administrator's password:
SeDiskOperatorPrivilege:
  BUILTIN\Administrators
  DOMAIN\Domain Admins

3.9.2. Enabling Windows ACL support

To configure shares that support Windows ACLs, you must enable this feature in Samba.

Prerequisites

  • A user share is configured on the Samba server.

Procedure

  1. To enable it globally for all shares, add the following settings to the [global] section of the /etc/samba/smb.conf file: 

    vfs objects = acl_xattr
map acl inherit = yes
store dos attributes = yes

    Alternatively, you can enable Windows ACL support for individual shares, by adding the same parameters to a share’s section instead.

  2. Restart the smb service: 

    # systemctl restart smb

3.9.3. Adding a share that uses Windows ACLs

You can create a share named example, that shares the content of the /srv/samba/example/ directory, and uses Windows ACLs.

Procedure

  1. Create the folder if it does not exists. For example: 

    # mkdir -p /srv/samba/example/

  2. If you run SELinux in enforcing mode, set the samba_share_t context on the directory: 

    # semanage fcontext -a -t samba_share_t "/srv/samba/example(/.*)?"
# restorecon -Rv /srv/samba/example/

  3. Add the example share to the /etc/samba/smb.conf file. For example, to add the share write-enabled: 

    [example]
	path = /srv/samba/example/
	read only = no
    Note

    Regardless of the file system ACLs; if you do not set read only = no, Samba shares the directory in read-only mode.

  4. If you have not enabled Windows ACL support in the [global] section for all shares, add the following parameters to the [example] section to enable this feature for this share: 

    vfs objects = acl_xattr
map acl inherit = yes
store dos attributes = yes

  5. Verify the /etc/samba/smb.conf file: 

    # testparm

  6. Open the required ports and reload the firewall configuration using the firewall-cmd utility: 

    # firewall-cmd --permanent --add-service=samba
# firewall-cmd --reload

  7. Restart the smb service: 

    # systemctl restart smb

3.9.4. Managing share permissions and file system ACLs of a share that uses Windows ACLs

To manage share permissions and file system ACLs on a Samba share that uses Windows ACLs, use a Windows applications, such as Computer Management. For details, see the Windows documentation. Alternatively, use the smbcacls utility to manage ACLs.

Note

To modify the file system permissions from Windows, you must use an account that has the SeDiskOperatorPrivilege privilege granted.

Additional resources

3.10. Managing ACLs on an SMB share using smbcacls

The smbcacls utility can list, set, and delete ACLs of files and directories stored on an SMB share. You can use smbcacls to manage file system ACLs:

  • On a local or remote Samba server that uses advanced Windows ACLs or POSIX ACLs
  • On Red Hat Enterprise Linux to remotely manage ACLs on a share hosted on Windows

3.10.1. Access control entries

Each ACL entry of a file system object contains Access Control Entries (ACE) in the following format: 

security_principal:access_right/inheritance_information/permissions

Example 3.3. Access control entries

If the AD\Domain Users group has Modify permissions that apply to This folder, subfolders, and files on Windows, the ACL contains the following ACE: 

AD\Domain Users:ALLOWED/OI|CI/CHANGE

An ACE contains the following parts:

Security principal
The security principal is the user, group, or SID the permissions in the ACL are applied to.
Access right
Defines if access to an object is granted or denied. The value can be ALLOWED or DENIED.
Inheritance information

The following values exist:

Table 3.1. Inheritance settings

ValueDescriptionMaps to

OI

Object Inherit

This folder and files

CI

Container Inherit

This folder and subfolders

IO

Inherit Only

The ACE does not apply to the current file or directory

ID

Inherited

The ACE was inherited from the parent directory

Additionally, the values can be combined as follows:

Table 3.2. Inheritance settings combinations

Value combinationsMaps to the Windows Applies to setting

OI|CI

This folder, subfolders, and files

OI|CI|IO

Subfolders and files only

CI|IO

Subfolders only

OI|IO

Files only

Permissions

This value can be either a hex value that represents one or more Windows permissions or an smbcacls alias:

  • A hex value that represents one or more Windows permissions.

    The following table displays the advanced Windows permissions and their corresponding value in hex format:

    Table 3.3. Windows permissions and their corresponding smbcacls value in hex format

    Windows permissionsHex values

    Full control

    0x001F01FF

    Traverse folder / execute file

    0x00100020

    List folder / read data

    0x00100001

    Read attributes

    0x00100080

    Read extended attributes

    0x00100008

    Create files / write data

    0x00100002

    Create folders / append data

    0x00100004

    Write attributes

    0x00100100

    Write extended attributes

    0x00100010

    Delete subfolders and files

    0x00100040

    Delete

    0x00110000

    Read permissions

    0x00120000

    Change permissions

    0x00140000

    Take ownership

    0x00180000

    Multiple permissions can be combined as a single hex value using the bit-wise OR operation. For details, see ACE mask calculation.

  • An smbcacls alias. The following table displays the available aliases:

    Table 3.4. Existing smbcacls aliases and their corresponding Windows permission

    smbcacls aliasMaps to Windows permission

    R

    Read

    READ

    Read & execute

    W

    Special:

    • Create files / write data
    • Create folders / append data
    • Write attributes
    • Write extended attributes
    • Read permissions

    D

    Delete

    P

    Change permissions

    O

    Take ownership

    X

    Traverse / execute

    CHANGE

    Modify

    FULL

    Full control

    Note

    You can combine single-letter aliases when you set permissions. For example, you can set RD to apply the Windows permission Read and Delete. However, you can neither combine multiple non-single-letter aliases nor combine aliases and hex values.

3.10.2. Displaying ACLs using smbcacls

To display ACLs on an SMB share, use the smbcacls utility. If you run smbcacls without any operation parameter, such as --add, the utility displays the ACLs of a file system object.

Procedure

For example, to list the ACLs of the root directory of the //server/example share: 

# smbcacls //server/example / -U "DOMAIN\administrator"
Enter DOMAIN\administrator's password:
REVISION:1
CONTROL:SR|PD|DI|DP
OWNER:AD\Administrators
GROUP:AD\Domain Users
ACL:AD\Administrator:ALLOWED/OI|CI/FULL
ACL:AD\Domain Users:ALLOWED/OI|CI/CHANGE
ACL:AD\Domain Guests:ALLOWED/OI|CI/0x00100021

The output of the command displays:

  • REVISION: The internal Windows NT ACL revision of the security descriptor
  • CONTROL: Security descriptor control
  • OWNER: Name or SID of the security descriptor’s owner
  • GROUP: Name or SID of the security descriptor’s group
  • ACL entries. For details, see Access control entries.

3.10.3. ACE mask calculation

In most situations, when you add or update an ACE, you use the smbcacls aliases listed in Existing smbcacls aliases and their corresponding Windows permission.

However, if you want to set advanced Windows permissions as listed in Windows permissions and their corresponding smbcacls value in hex format, you must use the bit-wise OR operation to calculate the correct value. You can use the following shell command to calculate the value: 

# echo $(printf '0x%X' $(( hex_value_1 | hex_value_2 | ... )))

Example 3.4. Calculating an ACE Mask

You want to set the following permissions:

  • Traverse folder / execute file (0x00100020)
  • List folder / read data (0x00100001)
  • Read attributes (0x00100080)

To calculate the hex value for the previous permissions, enter: 

# echo $(printf '0x%X' $(( 0x00100020 | 0x00100001 | 0x00100080 )))
0x1000A1

Use the returned value when you set or update an ACE.

3.10.4. Adding, updating, and removing an ACL using smbcacls

Depending on the parameter you pass to the smbcacls utility, you can add, update, and remove ACLs from a file or directory.

Adding an ACL

To add an ACL to the root of the //server/example share that grants CHANGE permissions for This folder, subfolders, and files to the AD\Domain Users group: 

# smbcacls //server/example / -U "DOMAIN\administrator --add ACL:"AD\Domain Users":ALLOWED/OI|CI/CHANGE
Updating an ACL

Updating an ACL is similar to adding a new ACL. You update an ACL by overriding the ACL using the --modify parameter with an existing security principal. If smbcacls finds the security principal in the ACL list, the utility updates the permissions. Otherwise the command fails with an error: 

ACL for SID principal_name not found

For example, to update the permissions of the AD\Domain Users group and set them to READ for This folder, subfolders, and files: 

# smbcacls //server/example / -U "DOMAIN\administrator --modify ACL:"AD\Domain Users":ALLOWED/OI|CI/READ
Deleting an ACL

To delete an ACL, pass the --delete parameter with the exact ACL to the smbcacls utility. For example: 

# smbcacls //server/example / -U "DOMAIN\administrator --delete ACL:"AD\Domain Users":ALLOWED/OI|CI/READ

3.11. Enabling users to share directories on a Samba server

On a Samba server, you can configure that users can share directories without root permissions.

3.11.1. Enabling the user shares feature

Before users can share directories, the administrator must enable user shares in Samba.

For example, to enable only members of the local example group to create user shares.

Procedure

  1. Create the local example group, if it does not exist: 

    # groupadd example

  2. Prepare the directory for Samba to store the user share definitions and set its permissions properly. For example:

    1. Create the directory: 

      # mkdir -p /var/lib/samba/usershares/

    2. Set write permissions for the example group: 

      # chgrp example /var/lib/samba/usershares/
# chmod 1770 /var/lib/samba/usershares/
    3. Set the sticky bit to prevent users to rename or delete files stored by other users in this directory.

  3. Edit the /etc/samba/smb.conf file and add the following to the [global] section:

    1. Set the path to the directory you configured to store the user share definitions. For example: 

      usershare path = /var/lib/samba/usershares/

    2. Set how many user shares Samba allows to be created on this server. For example: 

      usershare max shares = 100

      If you use the default of 0 for the usershare max shares parameter, user shares are disabled.

    3. Optionally, set a list of absolute directory paths. For example, to configure that Samba only allows to share subdirectories of the /data and /srv directory to be shared, set: 

      usershare prefix allow list = /data /srv

    For a list of further user share-related parameters you can set, see the USERSHARES section in the smb.conf(5) man page.

  4. Verify the /etc/samba/smb.conf file: 

    # testparm

  5. Reload the Samba configuration: 

    # smbcontrol all reload-config

    Users are now able to create user shares.

3.11.2. Adding a user share

After you enabled the user share feature in Samba, users can share directories on the Samba server without root permissions by running the net usershare add command.

Synopsis of the net usershare add command:

net usershare add share_name path [[ comment ] | [ ACLs ]] [ guest_ok=y|n ]

Important

If you set ACLs when you create a user share, you must specify the comment parameter prior to the ACLs. To set an empty comment, use an empty string in double quotes.

Note that users can only enable guest access on a user share, if the administrator set usershare allow guests = yes in the [global] section in the /etc/samba/smb.conf file.

Example 3.5. Adding a user share

A user wants to share the /srv/samba/ directory on a Samba server. The share should be named example, have no comment set, and should be accessible by guest users. Additionally, the share permissions should be set to full access for the AD\Domain Users group and read permissions for other users. To add this share, run as the user: 

$ net usershare add example /srv/samba/ "" "AD\Domain Users":F,Everyone:R guest_ok=yes

3.11.3. Updating settings of a user share

To update settings of a user share, override the share by using the net usershare add command with the same share name and the new settings. See Adding a user share.

3.11.4. Displaying information about existing user shares

Users can enter the net usershare info command on a Samba server to display user shares and their settings.

Prerequisites

  • A user share is configured on the Samba server.

Procedure

  1. To display all user shares created by any user: 

    $ net usershare info -l
[share_1]
path=/srv/samba/
comment=
usershare_acl=Everyone:R,host_name\user:F,
guest_ok=y
...

    To list only shares created by the user who runs the command, omit the -l parameter.

  2. To display only the information about specific shares, pass the share name or wild cards to the command. For example, to display the information about shares whose name starts with share_: 

    $ net usershare info -l share_*

3.11.5. Listing user shares

If you want to list only the available user shares without their settings on a Samba server, use the net usershare list command.

Prerequisites

  • A user share is configured on the Samba server.

Procedure

  1. To list the shares created by any user: 

    $ net usershare list -l
share_1
share_2
...

    To list only shares created by the user who runs the command, omit the -l parameter.

  2. To list only specific shares, pass the share name or wild cards to the command. For example, to list only shares whose name starts with share_: 

    $ net usershare list -l share_*

3.11.6. Deleting a user share

To delete a user share, use the command net usershare delete command as the user who created the share or as the root user.

Prerequisites

  • A user share is configured on the Samba server.

Procedure

$ net usershare delete share_name

3.12. Configuring a share to allow access without authentication

In certain situations, you want to share a directory to which users can connect without authentication. To configure this, enable guest access on a share.

Warning

Shares that do not require authentication can be a security risk.

3.12.1. Enabling guest access to a share

If guest access is enabled on a share, Samba maps guest connections to the operating system account set in the guest account parameter. Guest users can access files on this share if at least one of the following conditions is satisfied:

  • The account is listed in file system ACLs
  • The POSIX permissions for other users allow it

Example 3.6. Guest share permissions

If you configured Samba to map the guest account to nobody, which is the default, the ACLs in the following example:

  • Allow guest users to read file1.txt
  • Allow guest users to read and modify file2.txt
  • Prevent guest users to read or modify file3.txt 
-rw-r--r--. 1 root       root      1024 1. Sep 10:00 file1.txt
-rw-r-----. 1 nobody     root      1024 1. Sep 10:00 file2.txt
-rw-r-----. 1 root       root      1024 1. Sep 10:00 file3.txt

Procedure

  1. Edit the /etc/samba/smb.conf file:

    1. If this is the first guest share you set up on this server:

      1. Set map to guest = Bad User in the [global] section: 

        [global]
        ...
        map to guest = Bad User

        With this setting, Samba rejects login attempts that use an incorrect password unless the user name does not exist. If the specified user name does not exist and guest access is enabled on a share, Samba treats the connection as a guest log in.

      2. By default, Samba maps the guest account to the nobody account on Red Hat Enterprise Linux. Alternatively, you can set a different account. For example: 

        [global]
        ...
        guest account = user_name

        The account set in this parameter must exist locally on the Samba server. For security reasons, Red Hat recommends using an account that does not have a valid shell assigned.

    2. Add the guest ok = yes setting to the [example] share section: 

      [example]
        ...
        guest ok = yes

  2. Verify the /etc/samba/smb.conf file: 

    # testparm

  3. Reload the Samba configuration: 

    # smbcontrol all reload-config

3.13. Configuring Samba for macOS clients

The fruit virtual file system (VFS) Samba module provides enhanced compatibility with Apple server message block (SMB) clients.

3.13.1. Optimizing the Samba configuration for providing file shares for macOS clients

This section describes how to configure the fruit module for all Samba shares hosted on the server to optimize Samba file shares for macOS clients.

Note

Red Hat recommends enabling the fruit module globally. Clients using macOS negotiate the server server message block version 2 (SMB2) Apple (AAPL) protocol extensions when the client establishes the first connection to the server. If the client first connects to a share without AAPL extensions enabled, the client does not use the extensions for any share of the server.

Prerequisites

  • Samba is configured as a file server.

Procedure

  1. Edit the /etc/samba/smb.conf file, and enable the fruit and streams_xattr VFS modules in the [global] section: 

    vfs objects = fruit streams_xattr
    Important

    You must enable the fruit module before enabling streams_xattr. The fruit module uses alternate data streams (ADS). For this reason, you must also enable the streams_xattr module.

  2. Optionally, to provide macOS Time Machine support on a share, add the following setting to the share configuration in the /etc/samba/smb.conf file: 

    fruit:time machine = yes

  3. Verify the /etc/samba/smb.conf file: 

    # testparm

  4. Reload the Samba configuration: 

    # smbcontrol all reload-config

Additional resources

3.14. Using the smbclient utility to access an SMB share

The smbclient utility enables you to access file shares on an SMB server, similarly to a command-line FTP client. You can use it, for example, to upload and download files to and from a share.

Prerequisites

  • The samba-client package is installed.

3.14.1. How the smbclient interactive mode works

For example, to authenticate to the example share hosted on server using the DOMAIN\user account: 

# smbclient -U "DOMAIN\user" //server/example
Enter domain\user's password:
Try "help" to get a list of possible commands.
smb: \>

After smbclient connected successfully to the share, the utility enters the interactive mode and shows the following prompt: 

smb: \>

To display all available commands in the interactive shell, enter: 

smb: \> help

To display the help for a specific command, enter: 

smb: \> help command_name

Additional resources

  • smbclient(1) man page

3.14.2. Using smbclient in interactive mode

If you use smbclient without the -c parameter, the utility enters the interactive mode. The following procedure shows how to connect to an SMB share and download a file from a subdirectory.

Procedure

  1. Connect to the share: 

    # smbclient -U "DOMAIN\user_name" //server_name/share_name

  2. Change into the /example/ directory: 

    smb: \> d /example/

  3. List the files in the directory: 

    smb: \example\> ls
  .                    D         0  Thu Nov 1 10:00:00 2018
  ..                   D         0  Thu Nov 1 10:00:00 2018
  example.txt          N   1048576  Thu Nov 1 10:00:00 2018

         9950208 blocks of size 1024. 8247144 blocks available

  4. Download the example.txt file: 

    smb: \example\> get example.txt
getting file \directory\subdirectory\example.txt of size 1048576 as example.txt (511975,0 KiloBytes/sec) (average 170666,7 KiloBytes/sec)

  5. Disconnect from the share: 

    smb: \example\> exit

3.14.3. Using smbclient in scripting mode

If you pass the -c parameter to smbclient, you can automatically execute the commands on the remote SMB share. This enables you to use smbclient in scripts.

The following procedure shows how to connect to an SMB share and download a file from a subdirectory.

Procedure

  • Use the following command to connect to the share, change into the example directory, download the example.txt file: 
# smbclient -U DOMAIN\user_name //server_name/share_name -c "cd /example/ ; get example.txt ; exit"

3.15. Setting up Samba as a print server

If you set up Samba as a print server, clients in your network can use Samba to print. Additionally, Windows clients can, if configured, download the driver from the Samba server.

Parts of this section were adopted from the Setting up Samba as a Print Server documentation published in the Samba Wiki. License: CC BY 4.0. Authors and contributors: See the history tab on the Wiki page.

Prerequisites

Samba has been set up in one of the following modes:

3.15.1. Enabling print server support in Samba

By default, print server support is not enabled in Samba. To use Samba as a print server, you must configure Samba accordingly.

Note

Print jobs and printer operations require remote procedure calls (RPCs). By default, Samba starts the rpcd_spoolss service on demand to manage RPCs. During the first RPC call, or when you update the printer list in CUPS, Samba retrieves the printer information from CUPS. This can require approximately 1 second per printer. Therefore, if you have more than 50 printers, tune the rpcd_spoolss settings.

Prerequisites

  • The printers are configured in a CUPS server.

    For details about configuring printers in CUPS, see the documentation provided in the CUPS web console (https://printserver:631/help) on the print server.

Procedure

  1. Edit the /etc/samba/smb.conf file:

    1. Add the [printers] section to enable the printing backend in Samba: 

      [printers]
        comment = All Printers
        path = /var/tmp/
        printable = yes
        create mask = 0600
      Important

      The [printers] share name is hard-coded and cannot be changed.

    2. If the CUPS server runs on a different host or port, specify the setting in the [printers] section: 

      cups server = printserver.example.com:631

    3. If you have many printers, set the number of idle seconds to a higher value than the numbers of printers connected to CUPS. For example, if you have 100 printers, set in the [global] section: 

      rpcd_spoolss:idle_seconds = 200

      If this setting does not scale in your environment, also increase the number of rpcd_spoolss workers in the [global] section: 

      rpcd_spoolss:num_workers = 10

      By default, rpcd_spoolss starts 5 workers.

  2. Verify the /etc/samba/smb.conf file: 

    # testparm

  3. Open the required ports and reload the firewall configuration using the firewall-cmd utility: 

    # firewall-cmd --permanent --add-service=samba
# firewall-cmd --reload

  4. Restart the smb service: 

    # systemctl restart smb

    After restarting the service, Samba automatically shares all printers that are configured in the CUPS back end. If you want to manually share only specific printers, see Manually sharing specific printers.

Verification

  • Submit a print job. For example, to print a PDF file, enter: 

    # smbclient -Uuser //sambaserver.example.com/printer_name -c "print example.pdf"

3.15.2. Manually sharing specific printers

If you configured Samba as a print server, by default, Samba shares all printers that are configured in the CUPS back end. The following procedure explains how to share only specific printers.

Prerequisites

  • Samba is set up as a print server

Procedure

  1. Edit the /etc/samba/smb.conf file:

    1. In the [global] section, disable automatic printer sharing by setting: 

      load printers = no

    2. Add a section for each printer you want to share. For example, to share the printer named example in the CUPS back end as Example-Printer in Samba, add the following section: 

      [Example-Printer]
        path = /var/tmp/
        printable = yes
        printer name = example

      You do not need individual spool directories for each printer. You can set the same spool directory in the path parameter for the printer as you set in the [printers] section.

  2. Verify the /etc/samba/smb.conf file: 

    # testparm

  3. Reload the Samba configuration: 

    # smbcontrol all reload-config

3.16. Setting up automatic printer driver downloads for Windows clients on Samba print servers

If you are running a Samba print server for Windows clients, you can upload drivers and preconfigure printers. If a user connects to a printer, Windows automatically downloads and installs the driver locally on the client. The user does not require local administrator permissions for the installation. Additionally, Windows applies preconfigured driver settings, such as the number of trays.

Parts of this section were adopted from the Setting up Automatic Printer Driver Downloads for Windows Clients documentation published in the Samba Wiki. License: CC BY 4.0. Authors and contributors: See the history tab on the Wiki page.

Prerequisites

  • Samba is set up as a print server

3.16.1. Basic information about printer drivers

This section provides general information about printer drivers.

Supported driver model version

Samba only supports the printer driver model version 3 which is supported in Windows 2000 and later, and Windows Server 2000 and later. Samba does not support the driver model version 4, introduced in Windows 8 and Windows Server 2012. However, these and later Windows versions also support version 3 drivers.

Package-aware drivers

Samba does not support package-aware drivers.

Preparing a printer driver for being uploaded

Before you can upload a driver to a Samba print server:

  • Unpack the driver if it is provided in a compressed format.

  • Some drivers require to start a setup application that installs the driver locally on a Windows host. In certain situations, the installer extracts the individual files into the operating system’s temporary folder during the setup runs. To use the driver files for uploading:

    1. Start the installer.
    2. Copy the files from the temporary folder to a new location.
    3. Cancel the installation.

Ask your printer manufacturer for drivers that support uploading to a print server.

Providing 32-bit and 64-bit drivers for a printer to a client

To provide the driver for a printer for both 32-bit and 64-bit Windows clients, you must upload a driver with exactly the same name for both architectures. For example, if you are uploading the 32-bit driver named Example PostScript and the 64-bit driver named Example PostScript (v1.0), the names do not match. Consequently, you can only assign one of the drivers to a printer and the driver will not be available for both architectures.

3.16.2. Enabling users to upload and preconfigure drivers

To be able to upload and preconfigure printer drivers, a user or a group needs to have the SePrintOperatorPrivilege privilege granted. A user must be added into the printadmin group. Red Hat Enterprise Linux automatically creates this group when you install the samba package. The printadmin group gets assigned the lowest available dynamic system GID that is lower than 1000.

Procedure

  1. For example, to grant the SePrintOperatorPrivilege privilege to the printadmin group: 

    # net rpc rights grant "printadmin" SePrintOperatorPrivilege -U "DOMAIN\administrator"
Enter DOMAIN\administrator's password:
Successfully granted rights.
    Note

    In a domain environment, grant SePrintOperatorPrivilege to a domain group. This enables you to centrally manage the privilege by updating a user’s group membership.

  2. To list all users and groups having SePrintOperatorPrivilege granted: 

    # net rpc rights list privileges SePrintOperatorPrivilege -U "DOMAIN\administrator"
Enter administrator's password:
SePrintOperatorPrivilege:
  BUILTIN\Administrators
  DOMAIN\printadmin

3.16.3. Setting up the print$ share

Windows operating systems download printer drivers from a share named print$ from a print server. This share name is hard-coded in Windows and cannot be changed.

The following procedure explains how to share the /var/lib/samba/drivers/ directory as print$, and enable members of the local printadmin group to upload printer drivers.

Procedure

  1. Add the [print$] section to the /etc/samba/smb.conf file: 

    [print$]
        path = /var/lib/samba/drivers/
        read only = no
        write list = @printadmin
        force group = @printadmin
        create mask = 0664
        directory mask = 2775

    Using these settings:

    • Only members of the printadmin group can upload printer drivers to the share.
    • The group of new created files and directories will be set to printadmin.
    • The permissions of new files will be set to 664.
    • The permissions of new directories will be set to 2775.

  2. To upload only 64-bit drivers for all printers, include this setting in the [global] section in the /etc/samba/smb.conf file: 

    spoolss: architecture = Windows x64

    Without this setting, Windows only displays drivers for which you have uploaded at least the 32-bit version.

  3. Verify the /etc/samba/smb.conf file: 

    # testparm

  4. Reload the Samba configuration 

    # smbcontrol all reload-config

  5. Create the printadmin group if it does not exists: 

    # groupadd printadmin

  6. Grant the SePrintOperatorPrivilege privilege to the printadmin group. 

    # net rpc rights grant "printadmin" SePrintOperatorPrivilege -U "DOMAIN\administrator"
Enter DOMAIN\administrator's password:
Successfully granted rights.

  7. If you run SELinux in enforcing mode, set the samba_share_t context on the directory: 

    # semanage fcontext -a -t samba_share_t "/var/lib/samba/drivers(/.)?" # *restorecon -Rv /var/lib/samba/drivers/

  8. Set the permissions on the /var/lib/samba/drivers/ directory:

    • If you use POSIX ACLs, set: 

      # chgrp -R "printadmin" /var/lib/samba/drivers/
# chmod -R 2775 /var/lib/samba/drivers/

    • If you use Windows ACLs, set:

      PrincipalAccessApply to

      CREATOR OWNER

      Full control

      Subfolders and files only

      Authenticated Users

      Read & execute, List folder contents, Read

      This folder, subfolders, and files

      printadmin

      Full control

      This folder, subfolders, and files

      For details about setting ACLs on Windows, see the Windows documentation.

Additional resources

3.16.4. Creating a GPO to enable clients to trust the Samba print server

For security reasons, recent Windows operating systems prevent clients from downloading non-package-aware printer drivers from an untrusted server. If your print server is a member in an AD, you can create a Group Policy Object (GPO) in your domain to trust the Samba server.

Prerequisites

  • The Samba print server is a member of an AD domain.
  • The Windows computer you are using to create the GPO must have the Windows Remote Server Administration Tools (RSAT) installed. For details, see the Windows documentation.

Procedure

  1. Log into a Windows computer using an account that is allowed to edit group policies, such as the AD domain Administrator user.
  2. Open the Group Policy Management Console.

  3. Right-click to your AD domain and select Create a GPO in this domain, and Link it here.

    samba create new GPO
  4. Enter a name for the GPO, such as Legacy Printer Driver Policy and click OK. The new GPO will be displayed under the domain entry.
  5. Right-click to the newly-created GPO and select Edit to open the Group Policy Management Editor.

  6. Navigate to Computer Configuration → Policies → Administrative Templates → Printers.

    samba select printer GPO group

  7. On the right side of the window, double-click Point and Print Restriction to edit the policy:

    1. Enable the policy and set the following options:

      1. Select Users can only point and print to these servers and enter the fully-qualified domain name (FQDN) of the Samba print server to the field next to this option.

      2. In both check boxes under Security Prompts, select Do not show warning or elevation prompt.

        samba GPO point and print
    2. Click OK.

  8. Double-click Package Point and Print - Approved servers to edit the policy:

    1. Enable the policy and click the Show button.

    2. Enter the FQDN of the Samba print server.

      samba GPO approved servers
    3. Close both the Show Contents and the policy’s properties window by clicking OK.
  9. Close the Group Policy Management Editor.
  10. Close the Group Policy Management Console.

After the Windows domain members applied the group policy, printer drivers are automatically downloaded from the Samba server when a user connects to a printer.

Additional resources

  • For using group policies, see the Windows documentation.

3.16.5. Uploading drivers and preconfiguring printers

Use the Print Management application on a Windows client to upload drivers and preconfigure printers hosted on the Samba print server. For further details, see the Windows documentation.

3.17. Running Samba on a server with FIPS mode enabled

This section provides an overview of the limitations of running Samba with FIPS mode enabled. It also provides the procedure for enabling FIPS mode on a Red Hat Enterprise Linux host running Samba.

3.17.1. Limitations of using Samba in FIPS mode

The following Samba modes and features work in FIPS mode under the indicated conditions:

  • Samba as a domain member only in Active Directory (AD) or Red Hat Identity Management (IdM) environments with Kerberos authentication that uses AES ciphers.
  • Samba as a file server on an Active Directory domain member. However, this requires that clients use Kerberos to authenticate to the server.

Due to the increased security of FIPS, the following Samba features and modes do not work if FIPS mode is enabled:

  • NT LAN Manager (NTLM) authentication because RC4 ciphers are blocked
  • The server message block version 1 (SMB1) protocol
  • The stand-alone file server mode because it uses NTLM authentication
  • NT4-style domain controllers
  • NT4-style domain members. Note that Red Hat continues supporting the primary domain controller (PDC) functionality IdM uses in the background.
  • Password changes against the Samba server. You can only perform password changes using Kerberos against an Active Directory domain controller.

The following feature is not tested in FIPS mode and, therefore, is not supported by Red Hat:

  • Running Samba as a print server

3.17.2. Using Samba in FIPS mode

You can enable the FIPS mode on a RHEL host that runs Samba.

Prerequisites

  • Samba is configured on the Red Hat Enterprise Linux host.
  • Samba runs in a mode that is supported in FIPS mode.

Procedure

  1. Enable the FIPS mode on RHEL: 

    # fips-mode-setup --enable

  2. Reboot the server: 

    # reboot

  3. Use the testparm utility to verify the configuration: 

    # testparm -s

    If the command displays any errors or incompatibilities, fix them to ensure that Samba works correctly.

Additional resources

3.18. Tuning the performance of a Samba server

Learn what settings can improve the performance of Samba in certain situations, and which settings can have a negative performance impact.

Parts of this section were adopted from the Performance Tuning documentation published in the Samba Wiki. License: CC BY 4.0. Authors and contributors: See the history tab on the Wiki page.

Prerequisites

  • Samba is set up as a file or print server

3.18.1. Setting the SMB protocol version

Each new SMB version adds features and improves the performance of the protocol. The recent Windows and Windows Server operating systems always supports the latest protocol version. If Samba also uses the latest protocol version, Windows clients connecting to Samba benefit from the performance improvements. In Samba, the default value of the server max protocol is set to the latest supported stable SMB protocol version.

Note

To always have the latest stable SMB protocol version enabled, do not set the server max protocol parameter. If you set the parameter manually, you will need to modify the setting with each new version of the SMB protocol, to have the latest protocol version enabled.

The following procedure explains how to use the default value in the server max protocol parameter.

Procedure

  1. Remove the server max protocol parameter from the [global] section in the /etc/samba/smb.conf file.

  2. Reload the Samba configuration 

    # smbcontrol all reload-config

3.18.2. Tuning shares with directories that contain a large number of files

Linux supports case-sensitive file names. For this reason, Samba needs to scan directories for uppercase and lowercase file names when searching or accessing a file. You can configure a share to create new files only in lowercase or uppercase, which improves the performance.

Prerequisites

  • Samba is configured as a file server

Procedure

  1. Rename all files on the share to lowercase.

    Note

    Using the settings in this procedure, files with names other than in lowercase will no longer be displayed.

  2. Set the following parameters in the share’s section: 

    case sensitive = true
default case = lower
preserve case = no
short preserve case = no

    For details about the parameters, see their descriptions in the smb.conf(5) man page.

  3. Verify the /etc/samba/smb.conf file: 

    # testparm

  4. Reload the Samba configuration: 

    # smbcontrol all reload-config

After you applied these settings, the names of all newly created files on this share use lowercase. Because of these settings, Samba no longer needs to scan the directory for uppercase and lowercase, which improves the performance.

3.18.3. Settings that can have a negative performance impact

By default, the kernel in Red Hat Enterprise Linux is tuned for high network performance. For example, the kernel uses an auto-tuning mechanism for buffer sizes. Setting the socket options parameter in the /etc/samba/smb.conf file overrides these kernel settings. As a result, setting this parameter decreases the Samba network performance in most cases.

To use the optimized settings from the Kernel, remove the socket options parameter from the [global] section in the /etc/samba/smb.conf.

3.19. Configuring Samba to be compatible with clients that require an SMB version lower than the default

Samba uses a reasonable and secure default value for the minimum server message block (SMB) version it supports. However, if you have clients that require an older SMB version, you can configure Samba to support it.

3.19.1. Setting the minimum SMB protocol version supported by a Samba server

In Samba, the server min protocol parameter in the /etc/samba/smb.conf file defines the minimum server message block (SMB) protocol version the Samba server supports. You can change the minimum SMB protocol version.

Note

By default, Samba on RHEL 8.2 and later supports only SMB2 and newer protocol versions. Red Hat recommends to not use the deprecated SMB1 protocol. However, if your environment requires SMB1, you can manually set the server min protocol parameter to NT1 to re-enable SMB1.

Prerequisites

  • Samba is installed and configured.

Procedure

  1. Edit the /etc/samba/smb.conf file, add the server min protocol parameter, and set the parameter to the minimum SMB protocol version the server should support. For example, to set the minimum SMB protocol version to SMB3, add: 

    server min protocol = SMB3

  2. Restart the smb service: 

    # systemctl restart smb

Additional resources

  • smb.conf(5) man page

3.20. Frequently used Samba command-line utilities

This chapter describes frequently used commands when working with a Samba server.

3.20.1. Using the net ads join and net rpc join commands

Using the join subcommand of the net utility, you can join Samba to an AD or NT4 domain. To join the domain, you must create the /etc/samba/smb.conf file manually, and optionally update additional configurations, such as PAM.

Important

Red Hat recommends using the realm utility to join a domain. The realm utility automatically updates all involved configuration files.

Procedure

  1. Manually create the /etc/samba/smb.conf file with the following settings:

    • For an AD domain member: 

      [global]
workgroup = domain_name
security = ads
passdb backend = tdbsam
realm = AD_REALM

    • For an NT4 domain member: 

      [global]
workgroup = domain_name
security = user
passdb backend = tdbsam
  2. Add an ID mapping configuration for the * default domain and for the domain you want to join to the [global] section in the /etc/samba/smb.conf file.

  3. Verify the /etc/samba/smb.conf file: 

    # testparm

  4. Join the domain as the domain administrator:

    • To join an AD domain: 

      # net ads join -U "DOMAIN\administrator"

    • To join an NT4 domain: 

      # net rpc join -U "DOMAIN\administrator"

  5. Append the winbind source to the passwd and group database entry in the /etc/nsswitch.conf file: 

    passwd:     files winbind
group:      files winbind

  6. Enable and start the winbind service: 

    # systemctl enable --now winbind

  7. Optionally, configure PAM using the authselect utility.

    For details, see the authselect(8) man page.

  8. Optionally for AD environments, configure the Kerberos client.

    For details, see the documentation of your Kerberos client.

Additional resources

3.20.2. Using the net rpc rights command

In Windows, you can assign privileges to accounts and groups to perform special operations, such as setting ACLs on a share or upload printer drivers. On a Samba server, you can use the net rpc rights command to manage privileges.

Listing privileges you can set

To list all available privileges and their owners, use the net rpc rights list command. For example: 

# net rpc rights list -U "DOMAIN\administrator"
Enter DOMAIN\administrator's password:
     SeMachineAccountPrivilege  Add machines to domain
      SeTakeOwnershipPrivilege  Take ownership of files or other objects
             SeBackupPrivilege  Back up files and directories
            SeRestorePrivilege  Restore files and directories
     SeRemoteShutdownPrivilege  Force shutdown from a remote system
      SePrintOperatorPrivilege  Manage printers
           SeAddUsersPrivilege  Add users and groups to the domain
       SeDiskOperatorPrivilege  Manage disk shares
           SeSecurityPrivilege  System security
Granting privileges

To grant a privilege to an account or group, use the net rpc rights grant command.

For example, grant the SePrintOperatorPrivilege privilege to the DOMAIN\printadmin group: 

# net rpc rights grant "DOMAIN\printadmin" SePrintOperatorPrivilege -U "DOMAIN\administrator"
Enter DOMAIN\administrator's password:
Successfully granted rights.
Revoking privileges

To revoke a privilege from an account or group, use the net rpc rights revoke command.

For example, to revoke the SePrintOperatorPrivilege privilege from the DOMAIN\printadmin group: 

# net rpc rights remoke "DOMAIN\printadmin" SePrintOperatorPrivilege -U "DOMAIN\administrator"
Enter DOMAIN\administrator's password:
Successfully revoked rights.

3.20.3. Using the net rpc share command

The net rpc share command provides the capability to list, add, and remove shares on a local or remote Samba or Windows server.

Listing shares

To list the shares on an SMB server, use the net rpc share list command. Optionally, pass the -S server_name parameter to the command to list the shares of a remote server. For example: 

# net rpc share list -U "DOMAIN\administrator" -S server_name
Enter DOMAIN\administrator's password:
IPC$
share_1
share_2
...
Note

Shares hosted on a Samba server that have browseable = no set in their section in the /etc/samba/smb.conf file are not displayed in the output.

Adding a share

The net rpc share add command enables you to add a share to an SMB server.

For example, to add a share named example on a remote Windows server that shares the C:\example\ directory: 

# net rpc share add example="C:\example" -U "DOMAIN\administrator" -S server_name
Note

You must omit the trailing backslash in the path when specifying a Windows directory name.

To use the command to add a share to a Samba server:

  • The user specified in the -U parameter must have the SeDiskOperatorPrivilege privilege granted on the destination server.
  • You must write a script that adds a share section to the /etc/samba/smb.conf file and reloads Samba. The script must be set in the add share command parameter in the [global] section in /etc/samba/smb.conf. For further details, see the add share command description in the smb.conf(5) man page.
Removing a share

The net rpc share delete command enables you to remove a share from an SMB server.

For example, to remove the share named example from a remote Windows server: 

# net rpc share delete example -U "DOMAIN\administrator" -S server_name

To use the command to remove a share from a Samba server:

  • The user specified in the -U parameter must have the SeDiskOperatorPrivilege privilege granted.
  • You must write a script that removes the share’s section from the /etc/samba/smb.conf file and reloads Samba. The script must be set in the delete share command parameter in the [global] section in /etc/samba/smb.conf. For further details, see the delete share command description in the smb.conf(5) man page.

3.20.4. Using the net user command

The net user command enables you to perform the following actions on an AD DC or NT4 PDC:

  • List all user accounts
  • Add users
  • Remove Users
Note

Specifying a connection method, such as ads for AD domains or rpc for NT4 domains, is only required when you list domain user accounts. Other user-related subcommands can auto-detect the connection method.

Pass the -U user_name parameter to the command to specify a user that is allowed to perform the requested action.

Listing domain user accounts

To list all users in an AD domain: 

# net ads user -U "DOMAIN\administrator"

To list all users in an NT4 domain: 

# net rpc user -U "DOMAIN\administrator"
Adding a user account to the domain

On a Samba domain member, you can use the net user add command to add a user account to the domain.

For example, add the user account to the domain:

  1. Add the account: 

    # net user add user password -U "DOMAIN\administrator"
User user added

  2. Optionally, use the remote procedure call (RPC) shell to enable the account on the AD DC or NT4 PDC. For example: 

    # net rpc shell -U DOMAIN\administrator -S DC_or_PDC_name
Talking to domain DOMAIN (S-1-5-21-1424831554-512457234-5642315751)

net rpc> user edit disabled user: no
Set user's disabled flag from [yes] to [no]

net rpc> exit
Deleting a user account from the domain

On a Samba domain member, you can use the net user delete command to remove a user account from the domain.

For example, to remove the user account from the domain: 

# net user delete user -U "DOMAIN\administrator"
User user deleted

3.20.5. Using the rpcclient utility

The rpcclient utility enables you to manually execute client-side Microsoft Remote Procedure Call (MS-RPC) functions on a local or remote SMB server. However, most of the features are integrated into separate utilities provided by Samba. Use rpcclient only for testing MS-PRC functions.

Prerequisites

  • The samba-client package is installed.
Examples

For example, you can use the rpcclient utility to:

  • Manage the printer Spool Subsystem (SPOOLSS).

    Example 3.7. Assigning a Driver to a Printer

    # rpcclient server_name -U "DOMAIN\administrator" -c 'setdriver "printer_name" "driver_name"'
Enter DOMAIN\administrators password:
Successfully set printer_name to driver driver_name.

  • Retrieve information about an SMB server.

    Example 3.8. Listing all File Shares and Shared Printers

    # rpcclient server_name -U "DOMAIN\administrator" -c 'netshareenum'
Enter DOMAIN\administrators password:
netname: Example_Share
	remark:
	path:   C:\srv\samba\example_share\
	password:
netname: Example_Printer
	remark:
	path:   C:\var\spool\samba\
	password:

  • Perform actions using the Security Account Manager Remote (SAMR) protocol.

    Example 3.9. Listing Users on an SMB Server

    # rpcclient server_name -U "DOMAIN\administrator" -c 'enumdomusers'
Enter DOMAIN\administrators password:
user:[user1] rid:[0x3e8]
user:[user2] rid:[0x3e9]

    If you run the command against a standalone server or a domain member, it lists the users in the local database. Running the command against an AD DC or NT4 PDC lists the domain users.

Additional resources

  • rpcclient(1) man page

3.20.6. Using the samba-regedit application

Certain settings, such as printer configurations, are stored in the registry on the Samba server. You can use the ncurses-based samba-regedit application to edit the registry of a Samba server.

samba regedit

Prerequisites

  • The samba-client package is installed.

Procedure

To start the application, enter: 

# samba-regedit

Use the following keys:

  • Cursor up and cursor down: Navigate through the registry tree and the values.
  • Enter: Opens a key or edits a value.
  • Tab: Switches between the Key and Value pane.
  • Ctrl+C: Closes the application.

3.20.7. Using the smbcontrol utility

The smbcontrol utility enables you to send command messages to the smbd, nmbd, winbindd, or all of these services. These control messages instruct the service, for example, to reload its configuration.

Prerequisites

  • The samba-common-tools package is installed.

Procedure

  • Reload the configuration of the smbd, nmbd, winbindd services by sending the reload-config message type to the all destination: 
# smbcontrol all reload-config

Additional resources

  • smbcontrol(1) man page

3.20.8. Using the smbpasswd utility

The smbpasswd utility manages user accounts and passwords in the local Samba database.

Prerequisites

  • The samba-common-tools package is installed.

Procedure

  1. If you run the command as a user, smbpasswd changes the Samba password of the user who run the command. For example: 

    [user@server ~]$ smbpasswd
New SMB password: password
Retype new SMB password: password

  2. If you run smbpasswd as the root user, you can use the utility, for example, to:

    • Create a new user: 

      [root@server ~]# smbpasswd -a user_name
New SMB password: password
Retype new SMB password: password
Added user user_name.
      Note

      Before you can add a user to the Samba database, you must create the account in the local operating system. See the Adding a new user from the command line section in the Configuring basic system settings guide.

    • Enable a Samba user: 

      [root@server ~]# smbpasswd -e user_name
Enabled user user_name.

    • Disable a Samba user: 

      [root@server ~]# smbpasswd -x user_name
Disabled user user_name

    • Delete a user: 

      [root@server ~]# smbpasswd -x user_name
Deleted user user_name.

Additional resources

  • smbpasswd(8) man page

3.20.9. Using the smbstatus utility

The smbstatus utility reports on:

  • Connections per PID of each smbd daemon to the Samba server. This report includes the user name, primary group, SMB protocol version, encryption, and signing information.
  • Connections per Samba share. This report includes the PID of the smbd daemon, the IP of the connecting machine, the time stamp when the connection was established, encryption, and signing information.
  • A list of locked files. The report entries include further details, such as opportunistic lock (oplock) types

Prerequisites

  • The samba package is installed.
  • The smbd service is running.

Procedure

# smbstatus

Samba version 4.15.2
PID  Username              Group                Machine                            Protocol Version  Encryption  Signing
....-------------------------------------------------------------------------------------------------------------------------
963  DOMAIN\administrator  DOMAIN\domain users  client-pc  (ipv4:192.0.2.1:57786)  SMB3_02           -           AES-128-CMAC

Service  pid  Machine    Connected at                  Encryption  Signing:
....---------------------------------------------------------------------------
example  969  192.0.2.1  Thu Nov  1 10:00:00 2018 CEST  -           AES-128-CMAC

Locked files:
Pid  Uid    DenyMode   Access    R/W     Oplock      SharePath           Name      Time
....--------------------------------------------------------------------------------------------------------
969  10000  DENY_WRITE 0x120089  RDONLY  LEASE(RWH)  /srv/samba/example  file.txt  Thu Nov  1 10:00:00 2018

Additional resources

  • smbstatus(1) man page

3.20.10. Using the smbtar utility

The smbtar utility backs up the content of an SMB share or a subdirectory of it and stores the content in a tar archive. Alternatively, you can write the content to a tape device.

Prerequisites

  • The samba-client package is installed.

Procedure

  • Use the following command to back up the content of the demo directory on the //server/example/ share and store the content in the /root/example.tar archive: 

    # smbtar -s server -x example -u user_name -p password -t /root/example.tar

Additional resources

  • smbtar(1) man page

3.20.11. Using the wbinfo utility

The wbinfo utility queries and returns information created and used by the winbindd service.

Prerequisites

  • The samba-winbind-clients package is installed.

Procedure

You can use wbinfo, for example, to:

  • List domain users: 

    # wbinfo -u
AD\administrator
AD\guest
...

  • List domain groups: 

    # wbinfo -g
AD\domain computers
AD\domain admins
AD\domain users
...

  • Display the SID of a user: 

    # wbinfo --name-to-sid="AD\administrator"
S-1-5-21-1762709870-351891212-3141221786-500 SID_USER (1)

  • Display information about domains and trusts: 

    # wbinfo --trusted-domains --verbose
Domain Name   DNS Domain            Trust Type  Transitive  In   Out
BUILTIN                             None        Yes         Yes  Yes
server                              None        Yes         Yes  Yes
DOMAIN1       domain1.example.com   None        Yes         Yes  Yes
DOMAIN2       domain2.example.com   External    No          Yes  Yes

Additional resources

  • wbinfo(1) man page

3.21. Additional resources

Chapter 4. Setting up and configuring a BIND DNS server

BIND is a feature-rich DNS server that is fully compliant with the Internet Engineering Task Force (IETF) DNS standards and draft standards. For example, administrators frequently use BIND as:

  • Caching DNS server in the local network
  • Authoritative DNS server for zones
  • Secondary server to provide high availability for zones

4.1. Considerations about protecting BIND with SELinux or running it in a change-root environment

To secure a BIND installation, you can:

  • Run the named service without a change-root environment. In this case, SELinux in enforcing mode prevents exploitation of known BIND security vulnerabilities. By default, Red Hat Enterprise Linux uses SELinux in enforcing mode.

    Important

    Running BIND on RHEL with SELinux in enforcing mode is more secure than running BIND in a change-root environment.

  • Run the named-chroot service in a change-root environment.

    Using the change-root feature, administrators can define that the root directory of a process and its sub-processes is different to the / directory. When you start the named-chroot service, BIND switches its root directory to /var/named/chroot/. As a consequence, the service uses mount --bind commands to make the files and directories listed in /etc/named-chroot.files available in /var/named/chroot/, and the process has no access to files outside of /var/named/chroot/.

If you decide to use BIND:

  • In normal mode, use the named service.
  • In a change-root environment, use the named-chroot service. This requires that you install, additionally, the named-chroot package.

Additional resources

  • The Red Hat SELinux BIND security profile section in the named(8) man page

4.2. The BIND Administrator Reference Manual

The comprehensive BIND Administrator Reference Manual, that is included in the bind package, provides:

  • Configuration examples
  • Documentation on advanced features
  • A configuration reference
  • Security considerations

To display the BIND Administrator Reference Manual on a host that has the bind package installed, open the /usr/share/doc/bind/Bv9ARM.html file in a browser.

4.3. Configuring BIND as a caching DNS server

By default, the BIND DNS server resolves and caches successful and failed lookups. The service then answers requests to the same records from its cache. This significantly improves the speed of DNS lookups.

Prerequisites

  • The IP address of the server is static.

Procedure

  1. Install the bind and bind-utils packages: 

    # yum install bind bind-utils

    These packages provide BIND 9.11. If you require BIND 9.16, install the bind9.16 and bind9.16-utils packages.

  2. If you want to run BIND in a change-root environment install the bind-chroot package: 

    # yum install bind-chroot

    Note that running BIND on a host with SELinux in enforcing mode, which is default, is more secure.

  3. Edit the /etc/named.conf file, and make the following changes in the options statement:

    1. Update the listen-on and listen-on-v6 statements to specify on which IPv4 and IPv6 interfaces BIND should listen: 

      listen-on port 53 { 127.0.0.1; 192.0.2.1; };
listen-on-v6 port 53 { ::1; 2001:db8:1::1; };

    2. Update the allow-query statement to configure from which IP addresses and ranges clients can query this DNS server: 

      allow-query { localhost; 192.0.2.0/24; 2001:db8:1::/64; };

    3. Add an allow-recursion statement to define from which IP addresses and ranges BIND accepts recursive queries: 

      allow-recursion { localhost; 192.0.2.0/24; 2001:db8:1::/64; };
      Warning

      Do not allow recursion on public IP addresses of the server. Otherwise, the server can become part of large-scale DNS amplification attacks.

    4. By default, BIND resolves queries by recursively querying from the root servers to an authoritative DNS server. Alternatively, you can configure BIND to forward queries to other DNS servers, such as the ones of your provider. In this case, add a forwarders statement with the list of IP addresses of the DNS servers that BIND should forward queries to: 

      forwarders { 198.51.100.1; 203.0.113.5; };

      As a fall-back behavior, BIND resolves queries recursively if the forwarder servers do not respond. To disable this behavior, add a forward only; statement.

  4. Verify the syntax of the /etc/named.conf file: 

    # named-checkconf

    If the command displays no output, the syntax is correct.

  5. Update the firewalld rules to allow incoming DNS traffic: 

    # firewall-cmd --permanent --add-service=dns
# firewall-cmd --reload

  6. Start and enable BIND: 

    # systemctl enable --now named

    If you want to run BIND in a change-root environment, use the systemctl enable --now named-chroot command to enable and start the service.

Verification

  1. Use the newly set up DNS server to resolve a domain: 

    # dig @localhost www.example.org
...
www.example.org.    86400    IN    A    198.51.100.34

;; Query time: 917 msec
...

    This example assumes that BIND runs on the same host and responds to queries on the localhost interface.

    After querying a record for the first time, BIND adds the entry to its cache.

  2. Repeat the previous query: 

    # dig @localhost www.example.org
...
www.example.org.    85332    IN    A    198.51.100.34

;; Query time: 1 msec
...

    Because of the cached entry, further requests for the same record are significantly faster until the entry expires.

Next steps

  • Configure the clients in your network to use this DNS server. If a DHCP server provides the DNS server setting to the clients, update the DHCP server’s configuration accordingly.

Additional resources

4.4. Configuring logging on a BIND DNS server

The configuration in the default /etc/named.conf file, as provided by the bind package, uses the default_debug channel and logs messages to the /var/named/data/named.run file. The default_debug channel only logs entries when the server’s debug level is non-zero.

Using different channels and categories, you can configure BIND to write different events with a defined severity to separate files.

Prerequisites

  • BIND is already configured, for example, as a caching name server.
  • The named or named-chroot service is running.

Procedure

  1. Edit the /etc/named.conf file, and add category and channel phrases to the logging statement, for example: 

    logging {
    ...

    category notify { zone_transfer_log; };
    category xfer-in { zone_transfer_log; };
    category xfer-out { zone_transfer_log; };
    channel zone_transfer_log {
        file "/var/named/log/transfer.log" versions 10 size 50m;
        print-time yes;
        print-category yes;
        print-severity yes;
        severity info;
     };

     ...
};

    With this example configuration, BIND logs messages related to zone transfers to /var/named/log/transfer.log. BIND creates up to 10 versions of the log file and rotates them if they reach a maximum size of 50 MB.

    The category phrase defines to which channels BIND sends messages of a category.

    The channel phrase defines the destination of log messages including the number of versions, the maximum file size, and the severity level BIND should log to a channel. Additional settings, such as enabling logging the time stamp, category, and severity of an event are optional, but useful for debugging purposes.

  2. Create the log directory if it does not exist, and grant write permissions to the named user on this directory: 

    # mkdir /var/named/log/
# chown named:named /var/named/log/
# chmod 700 /var/named/log/

  3. Verify the syntax of the /etc/named.conf file: 

    # named-checkconf

    If the command displays no output, the syntax is correct.

  4. Restart BIND: 

    # systemctl restart named

    If you run BIND in a change-root environment, use the systemctl restart named-chroot command to restart the service.

Verification

  • Display the content of the log file: 

    # cat /var/named/log/transfer.log
...
06-Jul-2022 15:08:51.261 xfer-out: info: client @0x7fecbc0b0700 192.0.2.2#36121/key example-transfer-key (example.com): transfer of 'example.com/IN': AXFR started: TSIG example-transfer-key (serial 2022070603)
06-Jul-2022 15:08:51.261 xfer-out: info: client @0x7fecbc0b0700 192.0.2.2#36121/key example-transfer-key (example.com): transfer of 'example.com/IN': AXFR ended

Additional resources

4.5. Writing BIND ACLs

Controlling access to certain features of BIND can prevent unauthorized access and attacks, such as denial of service (DoS). BIND access control list (acl) statements are lists of IP addresses and ranges. Each ACL has a nickname that you can use in several statements, such as allow-query, to refer to the specified IP addresses and ranges.

Warning

BIND uses only the first matching entry in an ACL. For example, if you define an ACL { 192.0.2/24; !192.0.2.1; } and the host with IP address 192.0.2.1 connects, access is granted even if the second entry excludes this address.

BIND has the following built-in ACLs:

  • none: Matches no hosts.
  • any: Matches all hosts.
  • localhost: Matches the loopback addresses 127.0.0.1 and ::1, as well as the IP addresses of all interfaces on the server that runs BIND.
  • localnets: Matches the loopback addresses 127.0.0.1 and ::1, as well as all subnets the server that runs BIND is directly connected to.

Prerequisites

  • BIND is already configured, for example, as a caching name server.
  • The named or named-chroot service is running.

Procedure

  1. Edit the /etc/named.conf file and make the following changes:

    1. Add acl statements to the file. For example, to create an ACL named internal-networks for 127.0.0.1, 192.0.2.0/24, and 2001:db8:1::/64, enter: 

      acl internal-networks { 127.0.0.1; 192.0.2.0/24; 2001:db8:1::/64; };
acl dmz-networks { 198.51.100.0/24; 2001:db8:2::/64; };

    2. Use the ACL’s nickname in statements that support them, for example: 

      allow-query { internal-networks; dmz-networks; };
allow-recursion { internal-networks; };

  2. Verify the syntax of the /etc/named.conf file: 

    # named-checkconf

    If the command displays no output, the syntax is correct.

  3. Reload BIND: 

    # systemctl reload named

    If you run BIND in a change-root environment, use the systemctl reload named-chroot command to reload the service.

Verification

  • Execute an action that triggers a feature which uses the configured ACL. For example, the ACL in this procedure allows only recursive queries from the defined IP addresses. In this case, enter the following command on a host that is not within the ACL’s definition to attempt resolving an external domain: 

    # dig +short @192.0.2.1 www.example.com

    If the command returns no output, BIND denied access, and the ACL works. For a verbose output on the client, use the command without +short option: 

    # dig @192.0.2.1 www.example.com
...
;; WARNING: recursion requested but not available
...

Additional resources

4.6. Configuring zones on a BIND DNS server

A DNS zone is a database with resource records for a specific sub-tree in the domain space. For example, if you are responsible for the example.com domain, you can set up a zone for it in BIND. As a result, clients can, resolve www.example.com to the IP address configured in this zone.

4.6.1. The SOA record in zone files

The start of authority (SOA) record is a required record in a DNS zone. This record is important, for example, if multiple DNS servers are authoritative for a zone but also to DNS resolvers.

A SOA record in BIND has the following syntax: 

name class type mname rname serial refresh retry expire minimum

For better readability, administrators typically split the record in zone files into multiple lines with comments that start with a semicolon (;). Note that, if you split a SOA record, parentheses keep the record together: 

@ IN SOA ns1.example.com. hostmaster.example.com. (
                          2022070601 ; serial number
                          1d         ; refresh period
                          3h         ; retry period
                          3d         ; expire time
                          3h )       ; minimum TTL
Important

Note the trailing dot at the end of the fully-qualified domain names (FQDNs). FQDNs consist of multiple domain labels, separated by dots. Because the DNS root has an empty label, FQDNs end with a dot. Therefore, BIND appends the zone name to names without a trailing dot. A hostname without a trailing dot, for example, ns1.example.com would be expanded to ns1.example.com.example.com., which is not the correct address of the primary name server.

These are the fields in a SOA record:

  • name: The name of the zone, the so-called origin. If you set this field to @, BIND expands it to the zone name defined in /etc/named.conf.
  • class: In SOA records, you must set this field always to Internet (IN).
  • type: In SOA records, you must set this field always to SOA.
  • mname (master name): The hostname of the primary name server of this zone.
  • rname (responsible name): The email address of who is responsible for this zone. Note that the format is different. You must replace the at sign (@) with a dot (.).

  • serial: The version number of this zone file. Secondary name servers only update their copies of the zone if the serial number on the primary server is higher.

    The format can be any numeric value. A commonly-used format is <year><month><day><two-digit-number>. With this format, you can, theoretically, change the zone file up to a hundred times per day.

  • refresh: The amount of time secondary servers should wait before checking the primary server if the zone was updated.
  • retry: The amount of time after that a secondary server retries to query the primary server after a failed attempt.
  • expire: The amount of time after that a secondary server stops querying the primary server, if all previous attempts failed.
  • minimum: RFC 2308 changed the meaning of this field to the negative caching time. Compliant resolvers use it to determine how long to cache NXDOMAIN name errors.
Note

A numeric value in the refresh, retry, expire, and minimum fields define a time in seconds. However, for better readability, use time suffixes, such as m for minute, h for hours, and d for days. For example, 3h stands for 3 hours.

Additional resources

  • RFC 1035: Domain names - implementation and specification
  • RFC 1034: Domain names - concepts and facilities
  • RFC 2308: Negative caching of DNS queries (DNS cache)

4.6.2. Setting up a forward zone on a BIND primary server

Forward zones map names to IP addresses and other information. For example, if you are responsible for the domain example.com, you can set up a forward zone in BIND to resolve names, such as www.example.com.

Prerequisites

  • BIND is already configured, for example, as a caching name server.
  • The named or named-chroot service is running.

Procedure

  1. Add a zone definition to the /etc/named.conf file: 

    zone "example.com" {
    type master;
    file "example.com.zone";
    allow-query { any; };
    allow-transfer { none; };
};

    These settings define:

    • This server as the primary server (type master) for the example.com zone.
    • The /var/named/example.com.zone file is the zone file. If you set a relative path, as in this example, this path is relative to the directory you set in directory in the options statement.
    • Any host can query this zone. Alternatively, specify IP ranges or BIND access control list (ACL) nicknames to limit the access.
    • No host can transfer the zone. Allow zone transfers only when you set up secondary servers and only for the IP addresses of the secondary servers.

  2. Verify the syntax of the /etc/named.conf file: 

    # named-checkconf

    If the command displays no output, the syntax is correct.

  3. Create the /var/named/example.com.zone file, for example, with the following content: 

    $TTL 8h
@ IN SOA ns1.example.com. hostmaster.example.com. (
                          2022070601 ; serial number
                          1d         ; refresh period
                          3h         ; retry period
                          3d         ; expire time
                          3h )       ; minimum TTL

                  IN NS   ns1.example.com.
                  IN MX   10 mail.example.com.

www               IN A    192.0.2.30
www               IN AAAA 2001:db8:1::30
ns1               IN A    192.0.2.1
ns1               IN AAAA 2001:db8:1::1
mail              IN A    192.0.2.20
mail              IN AAAA 2001:db8:1::20

    This zone file:

    • Sets the default time-to-live (TTL) value for resource records to 8 hours. Without a time suffix, such as h for hour, BIND interprets the value as seconds.
    • Contains the required SOA resource record with details about the zone.
    • Sets ns1.example.com as an authoritative DNS server for this zone. To be functional, a zone requires at least one name server (NS) record. However, to be compliant with RFC 1912, you require at least two name servers.
    • Sets mail.example.com as the mail exchanger (MX) of the example.com domain. The numeric value in front of the host name is the priority of the record. Entries with a lower value have a higher priority.
    • Sets the IPv4 and IPv6 addresses of www.example.com, mail.example.com, and ns1.example.com.

  4. Set secure permissions on the zone file that allow only the named group to read it: 

    # chown root:named /var/named/example.com.zone
# chmod 640 /var/named/example.com.zone

  5. Verify the syntax of the /var/named/example.com.zone file: 

    # named-checkzone example.com /var/named/example.com.zone
zone example.com/IN: loaded serial 2022070601
OK

  6. Reload BIND: 

    # systemctl reload named

    If you run BIND in a change-root environment, use the systemctl reload named-chroot command to reload the service.

Verification

  • Query different records from the example.com zone, and verify that the output matches the records you have configured in the zone file: 

    # dig +short @localhost AAAA www.example.com
2001:db8:1::30

# dig +short @localhost NS example.com
ns1.example.com.

# dig +short @localhost A ns1.example.com
192.0.2.1

    This example assumes that BIND runs on the same host and responds to queries on the localhost interface.

Additional resources

4.6.3. Setting up a reverse zone on a BIND primary server

Reverse zones map IP addresses to names. For example, if you are responsible for IP range 192.0.2.0/24, you can set up a reverse zone in BIND to resolve IP addresses from this range to hostnames.

Note

If you create a reverse zone for whole classful networks, name the zone accordingly. For example, for the class C network 192.0.2.0/24, the name of the zone is 2.0.192.in-addr.arpa. If you want to create a reverse zone for a different network size, for example 192.0.2.0/28, the name of the zone is 28-2.0.192.in-addr.arpa.

Prerequisites

  • BIND is already configured, for example, as a caching name server.
  • The named or named-chroot service is running.

Procedure

  1. Add a zone definition to the /etc/named.conf file: 

    zone "2.0.192.in-addr.arpa" {
    type master;
    file "2.0.192.in-addr.arpa.zone";
    allow-query { any; };
    allow-transfer { none; };
};

    These settings define:

    • This server as the primary server (type master) for the 2.0.192.in-addr.arpa reverse zone.
    • The /var/named/2.0.192.in-addr.arpa.zone file is the zone file. If you set a relative path, as in this example, this path is relative to the directory you set in directory in the options statement.
    • Any host can query this zone. Alternatively, specify IP ranges or BIND access control list (ACL) nicknames to limit the access.
    • No host can transfer the zone. Allow zone transfers only when you set up secondary servers and only for the IP addresses of the secondary servers.

  2. Verify the syntax of the /etc/named.conf file: 

    # named-checkconf

    If the command displays no output, the syntax is correct.

  3. Create the /var/named/2.0.192.in-addr.arpa.zone file, for example, with the following content: 

    $TTL 8h
@ IN SOA ns1.example.com. hostmaster.example.com. (
                          2022070601 ; serial number
                          1d         ; refresh period
                          3h         ; retry period
                          3d         ; expire time
                          3h )       ; minimum TTL

                  IN NS   ns1.example.com.

1                 IN PTR  ns1.example.com.
30                IN PTR  www.example.com.

    This zone file:

    • Sets the default time-to-live (TTL) value for resource records to 8 hours. Without a time suffix, such as h for hour, BIND interprets the value as seconds.
    • Contains the required SOA resource record with details about the zone.
    • Sets ns1.example.com as an authoritative DNS server for this reverse zone. To be functional, a zone requires at least one name server (NS) record. However, to be compliant with RFC 1912, you require at least two name servers.
    • Sets the pointer (PTR) record for the 192.0.2.1 and 192.0.2.30 addresses.

  4. Set secure permissions on the zone file that only allow the named group to read it: 

    # chown root:named /var/named/2.0.192.in-addr.arpa.zone
# chmod 640 /var/named/2.0.192.in-addr.arpa.zone

  5. Verify the syntax of the /var/named/2.0.192.in-addr.arpa.zone file: 

    # named-checkzone 2.0.192.in-addr.arpa /var/named/2.0.192.in-addr.arpa.zone
zone 2.0.192.in-addr.arpa/IN: loaded serial 2022070601
OK

  6. Reload BIND: 

    # systemctl reload named

    If you run BIND in a change-root environment, use the systemctl reload named-chroot command to reload the service.

Verification

  • Query different records from the reverse zone, and verify that the output matches the records you have configured in the zone file: 

    # dig +short @localhost -x 192.0.2.1
ns1.example.com.

# dig +short @localhost -x 192.0.2.30
www.example.com.

    This example assumes that BIND runs on the same host and responds to queries on the localhost interface.

Additional resources

4.6.4. Updating a BIND zone file

In certain situations, for example if an IP address of a server changes, you must update a zone file. If multiple DNS servers are responsible for a zone, perform this procedure only on the primary server. Other DNS servers that store a copy of the zone will receive the update through a zone transfer.

Prerequisites

  • The zone is configured.
  • The named or named-chroot service is running.

Procedure

  1. Optional: Identify the path to the zone file in the /etc/named.conf file: 

    options {
    ...
    directory       "/var/named";
}

zone "example.com" {
    ...
    file "example.com.zone";
};

    You find the path to the zone file in the file statement in the zone’s definition. A relative path is relative to the directory set in directory in the options statement.

  2. Edit the zone file:

    1. Make the required changes.

    2. Increment the serial number in the start of authority (SOA) record.

      Important

      If the serial number is equal to or lower than the previous value, secondary servers will not update their copy of the zone.

  3. Verify the syntax of the zone file: 

    # named-checkzone example.com /var/named/example.com.zone
zone example.com/IN: loaded serial 2022062802
OK

  4. Reload BIND: 

    # systemctl reload named

    If you run BIND in a change-root environment, use the systemctl reload named-chroot command to reload the service.

Verification

  • Query the record you have added, modified, or removed, for example: 

    # dig +short @localhost A ns2.example.com
192.0.2.2

    This example assumes that BIND runs on the same host and responds to queries on the localhost interface.

Additional resources

4.6.5. DNSSEC zone signing using the automated key generation and zone maintenance features

You can sign zones with domain name system security extensions (DNSSEC) to ensure authentication and data integrity. Such zones contain additional resource records. Clients can use them to verify the authenticity of the zone information.

If you enable the DNSSEC policy feature for a zone, BIND performs the following actions automatically:

  • Creates the keys
  • Signs the zone
  • Maintains the zone, including re-signing and periodically replacing the keys.
Important

To enable external DNS servers to verify the authenticity of a zone, you must add the public key of the zone to the parent zone. Contact your domain provider or registry for further details on how to accomplish this.

This procedure uses the built-in default DNSSEC policy in BIND. This policy uses single ECDSAP256SHA key signatures. Alternatively, create your own policy to use custom keys, algorithms, and timings.

Prerequisites

  • BIND 9.16 or later is installed. To meet this requirement, install the bind9.16 package instead of bind.
  • The zone for which you want to enable DNSSEC is configured.
  • The named or named-chroot service is running.
  • The server synchronizes the time with a time server. An accurate system time is important for DNSSEC validation.

Procedure

  1. Edit the /etc/named.conf file, and add dnssec-policy default; to the zone for which you want to enable DNSSEC: 

    zone "example.com" {
    ...
    dnssec-policy default;
};

  2. Reload BIND: 

    # systemctl reload named

    If you run BIND in a change-root environment, use the systemctl reload named-chroot command to reload the service.

  3. BIND stores the public key in the /var/named/K<zone_name>.+<algorithm>+<key_ID>.key file. Use this file to display the public key of the zone in the format that the parent zone requires:

    • DS record format: 

      # dnssec-dsfromkey /var/named/Kexample.com.+013+61141.key
example.com. IN DS 61141 13 2 3E184188CF6D2521EDFDC3F07CFEE8D0195AACBD85E68BAE0620F638B4B1B027

    • DNSKEY format: 

      # grep DNSKEY /var/named/Kexample.com.+013+61141.key
example.com. 3600 IN DNSKEY 257 3 13 sjzT3jNEp120aSO4mPEHHSkReHUf7AABNnT8hNRTzD5cKMQSjDJin2I3 5CaKVcWO1pm+HltxUEt+X9dfp8OZkg==
  4. Request to add the public key of the zone to the parent zone. Contact your domain provider or registry for further details on how to accomplish this.

Verification

  1. Query your own DNS server for a record from the zone for which you enabled DNSSEC signing: 

    # dig +dnssec +short @localhost A www.example.com
192.0.2.30
A 13 3 28800 20220718081258 20220705120353 61141 example.com. e7Cfh6GuOBMAWsgsHSVTPh+JJSOI/Y6zctzIuqIU1JqEgOOAfL/Qz474 M0sgi54m1Kmnr2ANBKJN9uvOs5eXYw==

    This example assumes that BIND runs on the same host and responds to queries on the localhost interface.

  2. After the public key has been added to the parent zone and propagated to other servers, verify that the server sets the authenticated data (ad) flag on queries to the signed zone: 

    #  dig @localhost example.com +dnssec
...
;; flags: qr rd ra ad; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1
...

Additional resources

4.7. Configuring zone transfers among BIND DNS servers

Zone transfers ensure that all DNS servers that have a copy of the zone use up-to-date data.

Prerequisites

  • On the future primary server, the zone for which you want to set up zone transfers is already configured.
  • On the future secondary server, BIND is already configured, for example, as a caching name server.
  • On both servers, the named or named-chroot service is running.

Procedure

  1. On the existing primary server:

    1. Create a shared key, and append it to the /etc/named.conf file: 

      # tsig-keygen example-transfer-key | tee -a /etc/named.conf
key "example-transfer-key" {
        algorithm hmac-sha256;
        secret "q7ANbnyliDMuvWgnKOxMLi313JGcTZB5ydMW5CyUGXQ=";
};

      This command displays the output of the tsig-keygen command and automatically appends it to /etc/named.conf.

      You will require the output of the command later on the secondary server as well.

    2. Edit the zone definition in the /etc/named.conf file:

      1. In the allow-transfer statement, define that servers must provide the key specified in the example-transfer-key statement to transfer a zone: 

        zone "example.com" {
    ...
    allow-transfer { key example-transfer-key; };
};

        Alternatively, use BIND access control list (ACL) nicknames in the allow-transfer statement.

      2. By default, after a zone has been updated, BIND notifies all name servers which have a name server (NS) record in this zone. If you do not plan to add an NS record for the secondary server to the zone, you can, configure that BIND notifies this server anyway. For that, add the also-notify statement with the IP addresses of this secondary server to the zone: 

        zone "example.com" {
    ...
    also-notify { 192.0.2.2; 2001:db8:1::2; };
};

    3. Verify the syntax of the /etc/named.conf file: 

      # named-checkconf

      If the command displays no output, the syntax is correct.

    4. Reload BIND: 

      # systemctl reload named

      If you run BIND in a change-root environment, use the systemctl reload named-chroot command to reload the service.

  2. On the future secondary server:

    1. Edit the /etc/named.conf file as follows:

      1. Add the same key definition as on the primary server: 

        key "example-transfer-key" {
        algorithm hmac-sha256;
        secret "q7ANbnyliDMuvWgnKOxMLi313JGcTZB5ydMW5CyUGXQ=";
};

      2. Add the zone definition to the /etc/named.conf file: 

        zone "example.com" {
    type slave;
    file "slaves/example.com.zone";
    allow-query { any; };
    allow-transfer { none; };
    masters {
      192.0.2.1 key example-transfer-key;
      2001:db8:1::1 key example-transfer-key;
    };
};

        These settings state:

        • This server is a secondary server (type slave) for the example.com zone.
        • The /var/named/slaves/example.com.zone file is the zone file. If you set a relative path, as in this example, this path is relative to the directory you set in directory in the options statement. To separate zone files for which this server is secondary from primary ones, you can store them, for example, in the /var/named/slaves/ directory.
        • Any host can query this zone. Alternatively, specify IP ranges or ACL nicknames to limit the access.
        • No host can transfer the zone from this server.
        • The IP addresses of the primary server of this zone are 192.0.2.1 and 2001:db8:1::2. Alternatively, you can specify ACL nicknames. This secondary server will use the key named example-transfer-key to authenticate to the primary server.

    2. Verify the syntax of the /etc/named.conf file: 

      # named-checkconf

    3. Reload BIND: 

      # systemctl reload named

      If you run BIND in a change-root environment, use the systemctl reload named-chroot command to reload the service.

  3. Optional: Modify the zone file on the primary server and add an NS record for the new secondary server.

Verification

On the secondary server:

  1. Display the systemd journal entries of the named service: 

    # journalctl -u named
...
Jul 06 15:08:51 ns2.example.com named[2024]: zone example.com/IN: Transfer started.
Jul 06 15:08:51 ns2.example.com named[2024]: transfer of 'example.com/IN' from 192.0.2.1#53: connected using 192.0.2.2#45803
Jul 06 15:08:51 ns2.example.com named[2024]: zone example.com/IN: transferred serial 2022070101
Jul 06 15:08:51 ns2.example.com named[2024]: transfer of 'example.com/IN' from 192.0.2.1#53: Transfer status: success
Jul 06 15:08:51 ns2.example.com named[2024]: transfer of 'example.com/IN' from 192.0.2.1#53: Transfer completed: 1 messages, 29 records, 2002 bytes, 0.003 secs (667333 bytes/sec)

    If you run BIND in a change-root environment, use the journalctl -u named-chroot command to display the journal entries.

  2. Verify that BIND created the zone file: 

    # ls -l /var/named/slaves/
total 4
-rw-r--r--. 1 named named 2736 Jul  6 15:08 example.com.zone

    Note that, by default, secondary servers store zone files in a binary raw format.

  3. Query a record of the transferred zone from the secondary server: 

    # dig +short @192.0.2.2 AAAA www.example.com
2001:db8:1::30

    This example assumes that the secondary server you set up in this procedure listens on IP address 192.0.2.2.

Additional resources

4.8. Configuring response policy zones in BIND to override DNS records

Using DNS blocking and filtering, administrators can rewrite a DNS response to block access to certain domains or hosts. In BIND, response policy zones (RPZs) provide this feature. You can configure different actions for blocked entries, such as returning an NXDOMAIN error or not responding to the query.

If you have multiple DNS servers in your environment, use this procedure to configure the RPZ on the primary server, and later configure zone transfers to make the RPZ available on your secondary servers.

Prerequisites

  • BIND is already configured, for example, as a caching name server.
  • The named or named-chroot service is running.

Procedure

  1. Edit the /etc/named.conf file, and make the following changes:

    1. Add a response-policy definition to the options statement: 

      options {
    ...

    response-policy {
        zone "rpz.local";
    };

    ...
}

      You can set a custom name for the RPZ in the zone statement in response-policy. However, you must use the same name in the zone definition in the next step.

    2. Add a zone definition for the RPZ you set in the previous step: 

      zone "rpz.local" {
    type master;
    file "rpz.local";
    allow-query { localhost; 192.0.2.0/24; 2001:db8:1::/64; };
    allow-transfer { none; };
};

      These settings state:

      • This server is the primary server (type master) for the RPZ named rpz.local.
      • The /var/named/rpz.local file is the zone file. If you set a relative path, as in this example, this path is relative to the directory you set in directory in the options statement.
      • Any hosts defined in allow-query can query this RPZ. Alternatively, specify IP ranges or BIND access control list (ACL) nicknames to limit the access.
      • No host can transfer the zone. Allow zone transfers only when you set up secondary servers and only for the IP addresses of the secondary servers.

  2. Verify the syntax of the /etc/named.conf file: 

    # named-checkconf

    If the command displays no output, the syntax is correct.

  3. Create the /var/named/rpz.local file, for example, with the following content: 

    $TTL 10m
@ IN SOA ns1.example.com. hostmaster.example.com. (
                          2022070601 ; serial number
                          1h         ; refresh period
                          1m         ; retry period
                          3d         ; expire time
                          1m )       ; minimum TTL

                 IN NS    ns1.example.com.

example.org      IN CNAME .
*.example.org    IN CNAME .
example.net      IN CNAME rpz-drop.
*.example.net    IN CNAME rpz-drop.

    This zone file:

    • Sets the default time-to-live (TTL) value for resource records to 10 minutes. Without a time suffix, such as h for hour, BIND interprets the value as seconds.
    • Contains the required start of authority (SOA) resource record with details about the zone.
    • Sets ns1.example.com as an authoritative DNS server for this zone. To be functional, a zone requires at least one name server (NS) record. However, to be compliant with RFC 1912, you require at least two name servers.
    • Return an NXDOMAIN error for queries to example.org and hosts in this domain.
    • Drop queries to example.net and hosts in this domain.

    For a full list of actions and examples, see IETF draft: DNS Response Policy Zones (RPZ).

  4. Verify the syntax of the /var/named/rpz.local file: 

    # named-checkzone rpz.local /var/named/rpz.local
zone rpz.local/IN: loaded serial 2022070601
OK

  5. Reload BIND: 

    # systemctl reload named

    If you run BIND in a change-root environment, use the systemctl reload named-chroot command to reload the service.

Verification

  1. Attempt to resolve a host in example.org, that is configured in the RPZ to return an NXDOMAIN error: 

    # dig @localhost www.example.org
...
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 30286
...

    This example assumes that BIND runs on the same host and responds to queries on the localhost interface.

  2. Attempt to resolve a host in the example.net domain, that is configured in the RPZ to drop queries: 

    # dig @localhost www.example.net
...
;; connection timed out; no servers could be reached
...

Additional resources

Chapter 5. Exporting NFS shares

As a system administrator, you can use the NFS server to share a directory on your system over network.

5.1. Introduction to NFS

This section explains the basic concepts of the NFS service.

A Network File System (NFS) allows remote hosts to mount file systems over a network and interact with those file systems as though they are mounted locally. This enables you to consolidate resources onto centralized servers on the network.

The NFS server refers to the /etc/exports configuration file to determine whether the client is allowed to access any exported file systems. Once verified, all file and directory operations are available to the user.

5.2. Supported NFS versions

This section lists versions of NFS supported in Red Hat Enterprise Linux and their features.

Currently, Red Hat Enterprise Linux 8 supports the following major versions of NFS:

  • NFS version 3 (NFSv3) supports safe asynchronous writes and is more robust at error handling than the previous NFSv2; it also supports 64-bit file sizes and offsets, allowing clients to access more than 2 GB of file data.
  • NFS version 4 (NFSv4) works through firewalls and on the Internet, no longer requires an rpcbind service, supports Access Control Lists (ACLs), and utilizes stateful operations.

NFS version 2 (NFSv2) is no longer supported by Red Hat.

Default NFS version

The default NFS version in Red Hat Enterprise Linux 8 is 4.2. NFS clients attempt to mount using NFSv4.2 by default, and fall back to NFSv4.1 when the server does not support NFSv4.2. The mount later falls back to NFSv4.0 and then to NFSv3.

Features of minor NFS versions

Following are the features of NFSv4.2 in Red Hat Enterprise Linux 8:

Server-side copy
Enables the NFS client to efficiently copy data without wasting network resources using the copy_file_range() system call.
Sparse files
Enables files to have one or more holes, which are unallocated or uninitialized data blocks consisting only of zeroes. The lseek() operation in NFSv4.2 supports seek_hole() and seek_data(), which enables applications to map out the location of holes in the sparse file.
Space reservation
Permits storage servers to reserve free space, which prohibits servers to run out of space. NFSv4.2 supports the allocate() operation to reserve space, the deallocate() operation to unreserve space, and the fallocate() operation to preallocate or deallocate space in a file.
Labeled NFS
Enforces data access rights and enables SELinux labels between a client and a server for individual files on an NFS file system.
Layout enhancements
Provides the layoutstats() operation, which enables some Parallel NFS (pNFS) servers to collect better performance statistics.

Following are the features of NFSv4.1:

  • Enhances performance and security of network, and also includes client-side support for pNFS.
  • No longer requires a separate TCP connection for callbacks, which allows an NFS server to grant delegations even when it cannot contact the client: for example, when NAT or a firewall interferes.
  • Provides exactly once semantics (except for reboot operations), preventing a previous issue whereby certain operations sometimes returned an inaccurate result if a reply was lost and the operation was sent twice.

5.3. The TCP and UDP protocols in NFSv3 and NFSv4

NFSv4 requires the Transmission Control Protocol (TCP) running over an IP network.

NFSv3 could also use the User Datagram Protocol (UDP) in earlier Red Hat Enterprise Linux versions. In Red Hat Enterprise Linux 8, NFS over UDP is no longer supported. By default, UDP is disabled in the NFS server.

5.4. Services required by NFS

This section lists system services that are required for running an NFS server or mounting NFS shares. Red Hat Enterprise Linux starts these services automatically.

Red Hat Enterprise Linux uses a combination of kernel-level support and service processes to provide NFS file sharing. All NFS versions rely on Remote Procedure Calls (RPC) between clients and servers. To share or mount NFS file systems, the following services work together depending on which version of NFS is implemented:

nfsd
The NFS server kernel module that services requests for shared NFS file systems.
rpcbind
Accepts port reservations from local RPC services. These ports are then made available (or advertised) so the corresponding remote RPC services can access them. The rpcbind service responds to requests for RPC services and sets up connections to the requested RPC service. This is not used with NFSv4.
rpc.mountd
This process is used by an NFS server to process MOUNT requests from NFSv3 clients. It checks that the requested NFS share is currently exported by the NFS server, and that the client is allowed to access it. If the mount request is allowed, the nfs-mountd service replies with a Success status and provides the File-Handle for this NFS share back to the NFS client.
rpc.nfsd
This process enables explicit NFS versions and protocols the server advertises to be defined. It works with the Linux kernel to meet the dynamic demands of NFS clients, such as providing server threads each time an NFS client connects. This process corresponds to the nfs-server service.
lockd
This is a kernel thread that runs on both clients and servers. It implements the Network Lock Manager (NLM) protocol, which enables NFSv3 clients to lock files on the server. It is started automatically whenever the NFS server is run and whenever an NFS file system is mounted.
rpc.statd
This process implements the Network Status Monitor (NSM) RPC protocol, which notifies NFS clients when an NFS server is restarted without being gracefully brought down. The rpc-statd service is started automatically by the nfs-server service, and does not require user configuration. This is not used with NFSv4.
rpc.rquotad
This process provides user quota information for remote users. The rpc-rquotad service, which is provided by the quota-rpc package, has to be started by user when the nfs-server is started.
rpc.idmapd

This process provides NFSv4 client and server upcalls, which map between on-the-wire NFSv4 names (strings in the form of user@domain) and local UIDs and GIDs. For idmapd to function with NFSv4, the /etc/idmapd.conf file must be configured. At a minimum, the Domain parameter should be specified, which defines the NFSv4 mapping domain. If the NFSv4 mapping domain is the same as the DNS domain name, this parameter can be skipped. The client and server must agree on the NFSv4 mapping domain for ID mapping to function properly.

Only the NFSv4 server uses rpc.idmapd, which is started by the nfs-idmapd service. The NFSv4 client uses the keyring-based nfsidmap utility, which is called by the kernel on-demand to perform ID mapping. If there is a problem with nfsidmap, the client falls back to using rpc.idmapd.

The RPC services with NFSv4

The mounting and locking protocols have been incorporated into the NFSv4 protocol. The server also listens on the well-known TCP port 2049. As such, NFSv4 does not need to interact with rpcbind, lockd, and rpc-statd services. The nfs-mountd service is still required on the NFS server to set up the exports, but is not involved in any over-the-wire operations.

Additional resources

5.5. NFS host name formats

This section describes different formats that you can use to specify a host when mounting or exporting an NFS share.

You can specify the host in the following formats:

Single machine

Either of the following:

  • A fully-qualified domain name (that can be resolved by the server)
  • Host name (that can be resolved by the server)
  • An IP address.
IP networks

Either of the following formats is valid:

  • a.b.c.d/z, where a.b.c.d is the network and z is the number of bits in the netmask; for example 192.168.0.0/24.
  • a.b.c.d/netmask, where a.b.c.d is the network and netmask is the netmask; for example, 192.168.100.8/255.255.255.0.
Netgroups
The @group-name format , where group-name is the NIS netgroup name.

5.6. NFS server configuration

This section describes the syntax and options of two ways to configure exports on an NFS server:

  • Manually editing the /etc/exports configuration file
  • Using the exportfs utility on the command line

5.6.1. The /etc/exports configuration file

The /etc/exports file controls which file systems are exported to remote hosts and specifies options. It follows the following syntax rules:

  • Blank lines are ignored.
  • To add a comment, start a line with the hash mark (#).
  • You can wrap long lines with a backslash (\).
  • Each exported file system should be on its own individual line.
  • Any lists of authorized hosts placed after an exported file system must be separated by space characters.
  • Options for each of the hosts must be placed in parentheses directly after the host identifier, without any spaces separating the host and the first parenthesis.
Export entry

Each entry for an exported file system has the following structure: 

export host(options)

It is also possible to specify multiple hosts, along with specific options for each host. To do so, list them on the same line as a space-delimited list, with each host name followed by its respective options (in parentheses), as in: 

export host1(options1) host2(options2) host3(options3)

In this structure:

export
The directory being exported
host
The host or network to which the export is being shared
options
The options to be used for host

Example 5.1. A simple /etc/exports file

In its simplest form, the /etc/exports file only specifies the exported directory and the hosts permitted to access it: 

/exported/directory bob.example.com

Here, bob.example.com can mount /exported/directory/ from the NFS server. Because no options are specified in this example, NFS uses default options.

Important

The format of the /etc/exports file is very precise, particularly in regards to use of the space character. Remember to always separate exported file systems from hosts and hosts from one another with a space character. However, there should be no other space characters in the file except on comment lines.

For example, the following two lines do not mean the same thing: 

/home bob.example.com(rw)
/home bob.example.com (rw)

The first line allows only users from bob.example.com read and write access to the /home directory. The second line allows users from bob.example.com to mount the directory as read-only (the default), while the rest of the world can mount it read/write.

Default options

The default options for an export entry are:

ro
The exported file system is read-only. Remote hosts cannot change the data shared on the file system. To allow hosts to make changes to the file system (that is, read and write), specify the rw option.
sync
The NFS server will not reply to requests before changes made by previous requests are written to disk. To enable asynchronous writes instead, specify the option async.
wdelay
The NFS server will delay writing to the disk if it suspects another write request is imminent. This can improve performance as it reduces the number of times the disk must be accessed by separate write commands, thereby reducing write overhead. To disable this, specify the no_wdelay option, which is available only if the default sync option is also specified.
root_squash

This prevents root users connected remotely (as opposed to locally) from having root privileges; instead, the NFS server assigns them the user ID nobody. This effectively "squashes" the power of the remote root user to the lowest local user, preventing possible unauthorized writes on the remote server. To disable root squashing, specify the no_root_squash option.

To squash every remote user (including root), use the all_squash option. To specify the user and group IDs that the NFS server should assign to remote users from a particular host, use the anonuid and anongid options, respectively, as in: 

export host(anonuid=uid,anongid=gid)

Here, uid and gid are user ID number and group ID number, respectively. The anonuid and anongid options enable you to create a special user and group account for remote NFS users to share.

By default, access control lists (ACLs) are supported by NFS under Red Hat Enterprise Linux. To disable this feature, specify the no_acl option when exporting the file system.

Default and overridden options

Each default for every exported file system must be explicitly overridden. For example, if the rw option is not specified, then the exported file system is shared as read-only. The following is a sample line from /etc/exports which overrides two default options: 

/another/exported/directory 192.168.0.3(rw,async)

In this example, 192.168.0.3 can mount /another/exported/directory/ read and write, and all writes to disk are asynchronous.

5.6.2. The exportfs utility

The exportfs utility enables the root user to selectively export or unexport directories without restarting the NFS service. When given the proper options, the exportfs utility writes the exported file systems to /var/lib/nfs/xtab. Because the nfs-mountd service refers to the xtab file when deciding access privileges to a file system, changes to the list of exported file systems take effect immediately.

Common exportfs options

The following is a list of commonly-used options available for exportfs:

-r
Causes all directories listed in /etc/exports to be exported by constructing a new export list in /var/lib/nfs/etab. This option effectively refreshes the export list with any changes made to /etc/exports.
-a
Causes all directories to be exported or unexported, depending on what other options are passed to exportfs. If no other options are specified, exportfs exports all file systems specified in /etc/exports.
-o file-systems
Specifies directories to be exported that are not listed in /etc/exports. Replace file-systems with additional file systems to be exported. These file systems must be formatted in the same way they are specified in /etc/exports. This option is often used to test an exported file system before adding it permanently to the list of exported file systems.
-i
Ignores /etc/exports; only options given from the command line are used to define exported file systems.
-u
Unexports all shared directories. The command exportfs -ua suspends NFS file sharing while keeping all NFS services up. To re-enable NFS sharing, use exportfs -r.
-v
Verbose operation, where the file systems being exported or unexported are displayed in greater detail when the exportfs command is executed.

If no options are passed to the exportfs utility, it displays a list of currently exported file systems.

Additional resources

5.7. NFS and rpcbind

The rpcbind service maps Remote Procedure Call (RPC) services to the ports on which they listen. RPC processes notify rpcbind when they start, registering the ports they are listening on and the RPC program numbers they expect to serve. The client system then contacts rpcbind on the server with a particular RPC program number. The rpcbind service redirects the client to the proper port number so it can communicate with the requested service.

The Network File System Version 3 (NFSv3) requires the rpcbind service.

Because RPC-based services rely on rpcbind to make all connections with incoming client requests, rpcbind must be available before any of these services start.

Access control rules for rpcbind affect all RPC-based services. Alternatively, it is possible to specify access control rules for each of the NFS RPC daemons.

Additional resources

  • rpc.mountd(8) man page
  • rpc.statd(8) man page

5.8. Installing NFS

This procedure installs all packages necessary to mount or export NFS shares.

Procedure

  • Install the nfs-utils package: 

    # yum install nfs-utils

5.9. Starting the NFS server

This procedure describes how to start the NFS server, which is required to export NFS shares.

Prerequisites

  • For servers that support NFSv3 connections, the rpcbind service must be running. To verify that rpcbind is active, use the following command: 

    $ systemctl status rpcbind

    If the service is stopped, start and enable it: 

    $ systemctl enable --now rpcbind

Procedure

  • To start the NFS server and enable it to start automatically at boot, use the following command: 

    # systemctl enable --now nfs-server

Additional resources

5.10. Troubleshooting NFS and rpcbind

Because the rpcbind service provides coordination between RPC services and the port numbers used to communicate with them, it is useful to view the status of current RPC services using rpcbind when troubleshooting. The rpcinfo utility shows each RPC-based service with port numbers, an RPC program number, a version number, and an IP protocol type (TCP or UDP).

Procedure

  1. To make sure the proper NFS RPC-based services are enabled for rpcbind, use the following command: 

    # rpcinfo -p

    Example 5.2. rpcinfo -p command output

    The following is sample output from this command: 

       program vers proto   port  service
    100000    4   tcp    111  portmapper
    100000    3   tcp    111  portmapper
    100000    2   tcp    111  portmapper
    100000    4   udp    111  portmapper
    100000    3   udp    111  portmapper
    100000    2   udp    111  portmapper
    100005    1   udp  20048  mountd
    100005    1   tcp  20048  mountd
    100005    2   udp  20048  mountd
    100005    2   tcp  20048  mountd
    100005    3   udp  20048  mountd
    100005    3   tcp  20048  mountd
    100024    1   udp  37769  status
    100024    1   tcp  49349  status
    100003    3   tcp   2049  nfs
    100003    4   tcp   2049  nfs
    100227    3   tcp   2049  nfs_acl
    100021    1   udp  56691  nlockmgr
    100021    3   udp  56691  nlockmgr
    100021    4   udp  56691  nlockmgr
    100021    1   tcp  46193  nlockmgr
    100021    3   tcp  46193  nlockmgr
    100021    4   tcp  46193  nlockmgr

    If one of the NFS services does not start up correctly, rpcbind will be unable to map RPC requests from clients for that service to the correct port.

  2. In many cases, if NFS is not present in rpcinfo output, restarting NFS causes the service to correctly register with rpcbind and begin working: 

    # systemctl restart nfs-server

Additional resources

5.11. Configuring the NFS server to run behind a firewall

NFS requires the rpcbind service, which dynamically assigns ports for RPC services and can cause issues for configuring firewall rules. The following sections describe how to configure NFS versions to work behind a firewall if you want to support:

  • NFSv3

    This includes any servers that support NFSv3:

    • NFSv3-only servers
    • Servers that support both NFSv3 and NFSv4
  • NFSv4-only

5.11.1. Configuring the NFSv3-enabled server to run behind a firewall

The following procedure describes how to configure servers that support NFSv3 to run behind a firewall. This includes NFSv3-only servers and servers that support both NFSv3 and NFSv4.

Procedure

  1. To allow clients to access NFS shares behind a firewall, configure the firewall by running the following commands on the NFS server: 

    firewall-cmd --permanent --add-service mountd
firewall-cmd --permanent --add-service rpc-bind
firewall-cmd --permanent --add-service nfs

  2. Specify the ports to be used by the RPC service nlockmgr in the /etc/nfs.conf file as follows: 

    [lockd]

port=tcp-port-number
udp-port=udp-port-number

    Alternatively, you can specify nlm_tcpport and nlm_udpport in the /etc/modprobe.d/lockd.conf file.

  3. Open the specified ports in the firewall by running the following commands on the NFS server: 

    firewall-cmd --permanent --add-port=<lockd-tcp-port>/tcp
firewall-cmd --permanent --add-port=<lockd-udp-port>/udp

  4. Add static ports for rpc.statd by editing the [statd] section of the /etc/nfs.conf file as follows: 

    [statd]

port=port-number

  5. Open the added ports in the firewall by running the following commands on the NFS server: 

    firewall-cmd --permanent --add-port=<statd-tcp-port>/tcp
firewall-cmd --permanent --add-port=<statd-udp-port>/udp

  6. Reload the firewall configuration: 

    firewall-cmd --reload

  7. Restart the rpc-statd service first, and then restart the nfs-server service: 

    # systemctl restart rpc-statd.service
# systemctl restart nfs-server.service

    Alternatively, if you specified the lockd ports in the /etc/modprobe.d/lockd.conf file:

    1. Update the current values of /proc/sys/fs/nfs/nlm_tcpport and /proc/sys/fs/nfs/nlm_udpport: 

      # sysctl -w fs.nfs.nlm_tcpport=<tcp-port>
# sysctl -w fs.nfs.nlm_udpport=<udp-port>

    2. Restart the rpc-statd and nfs-server services: 

      # systemctl restart rpc-statd.service
# systemctl restart nfs-server.service

5.11.2. Configuring the NFSv4-only server to run behind a firewall

The following procedure describes how to configure the NFSv4-only server to run behind a firewall.

Procedure

  1. To allow clients to access NFS shares behind a firewall, configure the firewall by running the following command on the NFS server: 

    firewall-cmd --permanent --add-service nfs

  2. Reload the firewall configuration: 

    firewall-cmd --reload

  3. Restart the nfs-server: 

    # systemctl restart nfs-server

5.11.3. Configuring an NFSv3 client to run behind a firewall

The procedure to configure an NFSv3 client to run behind a firewall is similar to the procedure to configure an NFSv3 server to run behind a firewall.

If the machine you are configuring is both an NFS client and an NFS server, follow the procedure described in Configuring the NFSv3-enabled server to run behind a firewall.

The following procedure describes how to configure a machine that is an NFS client only to run behind a firewall.

Procedure

  1. To allow the NFS server to perform callbacks to the NFS client when the client is behind a firewall, add the rpc-bind service to the firewall by running the following command on the NFS client: 

    firewall-cmd --permanent --add-service rpc-bind

  2. Specify the ports to be used by the RPC service nlockmgr in the /etc/nfs.conf file as follows: 

    [lockd]

port=port-number
udp-port=upd-port-number

    Alternatively, you can specify nlm_tcpport and nlm_udpport in the /etc/modprobe.d/lockd.conf file.

  3. Open the specified ports in the firewall by running the following commands on the NFS client: 

    firewall-cmd --permanent --add-port=<lockd-tcp-port>/tcp
firewall-cmd --permanent --add-port=<lockd-udp-port>/udp

  4. Add static ports for rpc.statd by editing the [statd] section of the /etc/nfs.conf file as follows: 

    [statd]

port=port-number

  5. Open the added ports in the firewall by running the following commands on the NFS client: 

    firewall-cmd --permanent --add-port=<statd-tcp-port>/tcp
firewall-cmd --permanent --add-port=<statd-udp-port>/udp

  6. Reload the firewall configuration: 

    firewall-cmd --reload

  7. Restart the rpc-statd service: 

    # systemctl restart rpc-statd.service

    Alternatively, if you specified the lockd ports in the /etc/modprobe.d/lockd.conf file:

    1. Update the current values of /proc/sys/fs/nfs/nlm_tcpport and /proc/sys/fs/nfs/nlm_udpport: 

      # sysctl -w fs.nfs.nlm_tcpport=<tcp-port>
# sysctl -w fs.nfs.nlm_udpport=<udp-port>

    2. Restart the rpc-statd service: 

      # systemctl restart rpc-statd.service

5.11.4. Configuring an NFSv4 client to run behind a firewall

Perform this procedure only if the client is using NFSv4.0. In that case, it is necessary to open a port for NFSv4.0 callbacks.

This procedure is not needed for NFSv4.1 or higher because in the later protocol versions the server performs callbacks on the same connection that was initiated by the client.

Procedure

  1. To allow NFSv4.0 callbacks to pass through firewalls, set /proc/sys/fs/nfs/nfs_callback_tcpport and allow the server to connect to that port on the client as follows: 

    # echo "fs.nfs.nfs_callback_tcpport = <callback-port>" >/etc/sysctl.d/90-nfs-callback-port.conf
# sysctl -p /etc/sysctl.d/90-nfs-callback-port.conf

  2. Open the specified port in the firewall by running the following command on the NFS client: 

    firewall-cmd --permanent --add-port=<callback-port>/tcp

  3. Reload the firewall configuration: 

    firewall-cmd --reload

5.12. Exporting RPC quota through a firewall

If you export a file system that uses disk quotas, you can use the quota Remote Procedure Call (RPC) service to provide disk quota data to NFS clients.

Procedure

  1. Enable and start the rpc-rquotad service: 

    # systemctl enable --now rpc-rquotad
    Note

    The rpc-rquotad service is, if enabled, started automatically after starting the nfs-server service.

  2. To make the quota RPC service accessible behind a firewall, the TCP (or UDP, if UDP is enabled) port 875 need to be open. The default port number is defined in the /etc/services file.

    You can override the default port number by appending -p port-number to the RPCRQUOTADOPTS variable in the /etc/sysconfig/rpc-rquotad file.

  3. By default, remote hosts can only read quotas. If you want to allow clients to set quotas, append the -S option to the RPCRQUOTADOPTS variable in the /etc/sysconfig/rpc-rquotad file.

  4. Restart rpc-rquotad for the changes in the /etc/sysconfig/rpc-rquotad file to take effect: 

    # systemctl restart rpc-rquotad

5.13. Enabling NFS over RDMA (NFSoRDMA)

In Red Hat Enterprise Linux 8, Remote direct memory access (RDMA) service on RDMA-capable hardware provides Network File System (NFS) protocol support for high-speed file transfer over the network.

Procedure

  1. Install the rdma-core package: 

    # yum install rdma-core

  2. Verify the lines with xprtrdma and svcrdma are not commented out in the /etc/rdma/modules/rdma.conf file: 

    # NFS over RDMA client support
xprtrdma
# NFS over RDMA server support
svcrdma

  3. On the NFS server, create directory /mnt/nfsordma and export it to /etc/exports: 

    # mkdir /mnt/nfsordma
# echo "/mnt/nfsordma *(fsid=0,rw,async,insecure,no_root_squash)" >> /etc/exports

  4. On the NFS client, mount the nfs-share with server IP address, for example, 172.31.0.186: 

    # mount -o rdma,port=20049 172.31.0.186:/mnt/nfs-share /mnt/nfs

  5. Restart the nfs-server service: 

    # systemctl restart nfs-server

Additional resources

5.14. Additional resources

Chapter 6. Securing NFS

To minimize NFS security risks and protect data on the server, consider the following sections when exporting NFS file systems on a server or mounting them on a client.

6.1. NFS security with AUTH_SYS and export controls

NFS provides the following traditional options in order to control access to exported files:

  • The server restricts which hosts are allowed to mount which file systems either by IP address or by host name.
  • The server enforces file system permissions for users on NFS clients in the same way it does for local users. Traditionally, NFS does this using the AUTH_SYS call message (also called AUTH_UNIX), which relies on the client to state the UID and GIDs of the user. Be aware that this means that a malicious or misconfigured client might easily get this wrong and allow a user access to files that it should not.

To limit the potential risks, administrators often limits the access to read-only or squash user permissions to a common user and group ID. Unfortunately, these solutions prevent the NFS share from being used in the way it was originally intended.

Additionally, if an attacker gains control of the DNS server used by the system exporting the NFS file system, they can point the system associated with a particular hostname or fully qualified domain name to an unauthorized machine. At this point, the unauthorized machine is the system permitted to mount the NFS share, because no username or password information is exchanged to provide additional security for the NFS mount.

Wildcards should be used sparingly when exporting directories through NFS, as it is possible for the scope of the wildcard to encompass more systems than intended.

Additional resources

  • To secure NFS and rpcbind, use, for example, nftables and firewalld.
  • nft(8) man page
  • firewalld-cmd(1) man page

6.2. NFS security with AUTH_GSS

All version of NFS support RPCSEC_GSS and the Kerberos mechanism.

Unlike AUTH_SYS, with the RPCSEC_GSS Kerberos mechanism, the server does not depend on the client to correctly represent which user is accessing the file. Instead, cryptography is used to authenticate users to the server, which prevents a malicious client from impersonating a user without having that user’s Kerberos credentials. Using the RPCSEC_GSS Kerberos mechanism is the most straightforward way to secure mounts because after configuring Kerberos, no additional setup is needed.

6.3. Configuring an NFS server and client to use Kerberos

Kerberos is a network authentication system that allows clients and servers to authenticate to each other by using symmetric encryption and a trusted third party, the KDC. Red Hat recommends using Identity Management (IdM) for setting up Kerberos.

Prerequisites

  • The Kerberos Key Distribution Centre (KDC) is installed and configured.

Procedure

    • Create the nfs/hostname.domain@REALM principal on the NFS server side.
    • Create the host/hostname.domain@REALM principal on both the server and the client side.
    • Add the corresponding keys to keytabs for the client and server.

  2. On the server side, use the sec= option to enable the wanted security flavors. To enable all security flavors as well as non-cryptographic mounts: 

    /export *(sec=sys:krb5:krb5i:krb5p)

    Valid security flavors to use with the sec= option are:

    • sys: no cryptographic protection, the default
    • krb5: authentication only

    • krb5i: integrity protection

      • uses Kerberos V5 for user authentication and performs integrity checking of NFS operations using secure checksums to prevent data tampering.

    • krb5p: privacy protection

      • uses Kerberos V5 for user authentication, integrity checking, and encrypts NFS traffic to prevent traffic sniffing. This is the most secure setting, but it also involves the most performance overhead.

  3. On the client side, add sec=krb5 (or sec=krb5i, or sec=krb5p, depending on the setup) to the mount options: 

    # mount -o sec=krb5 server:/export /mnt

Additional resources

6.4. NFSv4 security options

NFSv4 includes ACL support based on the Microsoft Windows NT model, not the POSIX model, because of the Microsoft Windows NT model’s features and wide deployment.

Another important security feature of NFSv4 is the removal of the use of the MOUNT protocol for mounting file systems. The MOUNT protocol presented a security risk because of the way the protocol processed file handles.

6.5. File permissions on mounted NFS exports

Once the NFS file system is mounted as either read or read and write by a remote host, the only protection each shared file has is its permissions. If two users that share the same user ID value mount the same NFS file system on different client systems, they can modify each others' files. Additionally, anyone logged in as root on the client system can use the su - command to access any files with the NFS share.

By default, access control lists (ACLs) are supported by NFS under Red Hat Enterprise Linux. Red Hat recommends to keep this feature enabled.

By default, NFS uses root squashing when exporting a file system. This sets the user ID of anyone accessing the NFS share as the root user on their local machine to nobody. Root squashing is controlled by the default option root_squash; for more information about this option, see NFS server configuration.

When exporting an NFS share as read-only, consider using the all_squash option. This option makes every user accessing the exported file system take the user ID of the nobody user.

Chapter 7. Enabling pNFS SCSI layouts in NFS

You can configure the NFS server and client to use the pNFS SCSI layout for accessing data. pNFS SCSI is beneficial in use cases that involve longer-duration single-client access to a file.

Prerequisites

  • Both the client and the server must be able to send SCSI commands to the same block device. That is, the block device must be on a shared SCSI bus.
  • The block device must contain an XFS file system.
  • The SCSI device must support SCSI Persistent Reservations as described in the SCSI-3 Primary Commands specification.

7.1. The pNFS technology

The pNFS architecture improves the scalability of NFS. When a server implements pNFS, the client is able to access data through multiple servers concurrently. This can lead to performance improvements.

pNFS supports the following storage protocols or layouts on RHEL:

  • Files
  • Flexfiles
  • SCSI

7.2. pNFS SCSI layouts

The SCSI layout builds on the work of pNFS block layouts. The layout is defined across SCSI devices. It contains a sequential series of fixed-size blocks as logical units (LUs) that must be capable of supporting SCSI persistent reservations. The LU devices are identified by their SCSI device identification.

pNFS SCSI performs well in use cases that involve longer-duration single-client access to a file. An example might be a mail server or a virtual machine housing a cluster.

Operations between the client and the server

When an NFS client reads from a file or writes to it, the client performs a LAYOUTGET operation. The server responds with the location of the file on the SCSI device. The client might need to perform an additional operation of GETDEVICEINFO to determine which SCSI device to use. If these operations work correctly, the client can issue I/O requests directly to the SCSI device instead of sending READ and WRITE operations to the server.

Errors or contention between clients might cause the server to recall layouts or not issue them to the clients. In those cases, the clients fall back to issuing READ and WRITE operations to the server instead of sending I/O requests directly to the SCSI device.

To monitor the operations, see Monitoring pNFS SCSI layouts functionality.

Device reservations

pNFS SCSI handles fencing through the assignment of reservations. Before the server issues layouts to clients, it reserves the SCSI device to ensure that only registered clients may access the device. If a client can issue commands to that SCSI device but is not registered with the device, many operations from the client on that device fail. For example, the blkid command on the client fails to show the UUID of the XFS file system if the server has not given a layout for that device to the client.

The server does not remove its own persistent reservation. This protects the data within the file system on the device across restarts of clients and servers. In order to repurpose the SCSI device, you might need to manually remove the persistent reservation on the NFS server.

7.3. Checking for a SCSI device compatible with pNFS

This procedure checks if a SCSI device supports the pNFS SCSI layout.

Prerequisites

  • Install the sg3_utils package: 

    # yum install sg3_utils

Procedure

  • On both the server and client, check for the proper SCSI device support: 

    # sg_persist --in --report-capabilities --verbose path-to-scsi-device

    Ensure that the Persist Through Power Loss Active (PTPL_A) bit is set.

    Example 7.1. A SCSI device that supports pNFS SCSI

    The following is an example of sg_persist output for a SCSI device that supports pNFS SCSI. The PTPL_A bit reports 1. 

        inquiry cdb: 12 00 00 00 24 00
    Persistent Reservation In cmd: 5e 02 00 00 00 00 00 20 00 00
  LIO-ORG   block11           4.0
  Peripheral device type: disk
Report capabilities response:
  Compatible Reservation Handling(CRH): 1
  Specify Initiator Ports Capable(SIP_C): 1
  All Target Ports Capable(ATP_C): 1
  Persist Through Power Loss Capable(PTPL_C): 1
  Type Mask Valid(TMV): 1
  Allow Commands: 1
  Persist Through Power Loss Active(PTPL_A): 1
    Support indicated in Type mask:
      Write Exclusive, all registrants: 1
      Exclusive Access, registrants only: 1
      Write Exclusive, registrants only: 1
      Exclusive Access: 1
      Write Exclusive: 1
      Exclusive Access, all registrants: 1

Additional resources

  • sg_persist(8) man page

7.4. Setting up pNFS SCSI on the server

This procedure configures an NFS server to export a pNFS SCSI layout.

Procedure

  1. On the server, mount the XFS file system created on the SCSI device.

  2. Configure the NFS server to export NFS version 4.1 or higher. Set the following option in the [nfsd] section of the /etc/nfs.conf file: 

    [nfsd]

vers4.1=y

  3. Configure the NFS server to export the XFS file system over NFS with the pnfs option:

    Example 7.2. An entry in /etc/exports to export pNFS SCSI

    The following entry in the /etc/exports configuration file exports the file system mounted at /exported/directory/ to the allowed.example.com client as a pNFS SCSI layout: 

    /exported/directory allowed.example.com(pnfs)
    Note

    The exported file system must be created on the whole block device, not only on a partition.

Additional resources

7.5. Setting up pNFS SCSI on the client

This procedure configures an NFS client to mount a pNFS SCSI layout.

Prerequisites

Procedure

  • On the client, mount the exported XFS file system using NFS version 4.1 or higher: 

    # mount -t nfs -o nfsvers=4.1 host:/remote/export /local/directory

    Do not mount the XFS file system directly without NFS.

Additional resources

7.6. Releasing the pNFS SCSI reservation on the server

This procedure releases the persistent reservation that an NFS server holds on a SCSI device. This enables you to repurpose the SCSI device when you no longer need to export pNFS SCSI.

You must remove the reservation from the server. It cannot be removed from a different IT Nexus.

Prerequisites

  • Install the sg3_utils package: 

    # yum install sg3_utils

Procedure

  1. Query an existing reservation on the server: 

    # sg_persist --read-reservation path-to-scsi-device

    Example 7.3. Querying a reservation on /dev/sda

    # sg_persist --read-reservation /dev/sda

  LIO-ORG   block_1           4.0
  Peripheral device type: disk
  PR generation=0x8, Reservation follows:
    Key=0x100000000000000
    scope: LU_SCOPE,  type: Exclusive Access, registrants only

  2. Remove the existing registration on the server: 

    # sg_persist --out \
             --release \
             --param-rk=reservation-key \
             --prout-type=6 \
             path-to-scsi-device

    Example 7.4. Removing a reservation on /dev/sda

    # sg_persist --out \
             --release \
             --param-rk=0x100000000000000 \
             --prout-type=6 \
             /dev/sda

  LIO-ORG   block_1           4.0
  Peripheral device type: disk

Additional resources

  • sg_persist(8) man page

Chapter 8. Configuring the Squid caching proxy server

Squid is a proxy server that caches content to reduce bandwidth and load web pages more quickly. This chapter describes how to set up Squid as a proxy for the HTTP, HTTPS, and FTP protocol, as well as authentication and restricting access.

8.1. Setting up Squid as a caching proxy without authentication

You can configure Squid as a caching proxy without authentication. The procedure limits access to the proxy based on IP ranges.

Prerequisites

  • The procedure assumes that the /etc/squid/squid.conf file is as provided by the squid package. If you edited this file before, remove the file and reinstall the package.

Procedure

  1. Install the squid package: 

    # yum install squid

  2. Edit the /etc/squid/squid.conf file:

    1. Adapt the localnet access control lists (ACL) to match the IP ranges that should be allowed to use the proxy: 

      acl localnet src 192.0.2.0/24
acl localnet 2001:db8:1::/64

      By default, the /etc/squid/squid.conf file contains the http_access allow localnet rule that allows using the proxy from all IP ranges specified in localnet ACLs. Note that you must specify all localnet ACLs before the http_access allow localnet rule.

      Important

      Remove all existing acl localnet entries that do not match your environment.

    2. The following ACL exists in the default configuration and defines 443 as a port that uses the HTTPS protocol: 

      acl SSL_ports port 443

      If users should be able to use the HTTPS protocol also on other ports, add an ACL for each of these port: 

      acl SSL_ports port port_number

    3. Update the list of acl Safe_ports rules to configure to which ports Squid can establish a connection. For example, to configure that clients using the proxy can only access resources on port 21 (FTP), 80 (HTTP), and 443 (HTTPS), keep only the following acl Safe_ports statements in the configuration: 

      acl Safe_ports port 21
acl Safe_ports port 80
acl Safe_ports port 443

      By default, the configuration contains the http_access deny !Safe_ports rule that defines access denial to ports that are not defined in Safe_ports ACLs.

    4. Configure the cache type, the path to the cache directory, the cache size, and further cache type-specific settings in the cache_dir parameter: 

      cache_dir ufs /var/spool/squid 10000 16 256

      With these settings:

      • Squid uses the ufs cache type.
      • Squid stores its cache in the /var/spool/squid/ directory.
      • The cache grows up to 10000 MB.
      • Squid creates 16 level-1 sub-directories in the /var/spool/squid/ directory.

      • Squid creates 256 sub-directories in each level-1 directory.

        If you do not set a cache_dir directive, Squid stores the cache in memory.

  3. If you set a different cache directory than /var/spool/squid/ in the cache_dir parameter:

    1. Create the cache directory: 

      # mkdir -p path_to_cache_directory

    2. Configure the permissions for the cache directory: 

      # chown squid:squid path_to_cache_directory

    3. If you run SELinux in enforcing mode, set the squid_cache_t context for the cache directory: 

      # semanage fcontext -a -t squid_cache_t "path_to_cache_directory(/.*)?"
# restorecon -Rv path_to_cache_directory

      If the semanage utility is not available on your system, install the policycoreutils-python-utils package.

  4. Open the 3128 port in the firewall: 

    # firewall-cmd --permanent --add-port=3128/tcp
# firewall-cmd --reload

  5. Enable and start the squid service: 

    # systemctl enable --now squid

Verification steps

To verify that the proxy works correctly, download a web page using the curl utility: 

# curl -O -L "https://www.redhat.com/index.html" -x "proxy.example.com:3128"

If curl does not display any error and the index.html file was downloaded to the current directory, the proxy works.

8.2. Setting up Squid as a caching proxy with LDAP authentication

You can configure Squid as a caching proxy that uses LDAP to authenticate users. The procedure configures that only authenticated users can use the proxy.

Prerequisites

  • The procedure assumes that the /etc/squid/squid.conf file is as provided by the squid package. If you edited this file before, remove the file and reinstall the package.
  • An service user, such as uid=proxy_user,cn=users,cn=accounts,dc=example,dc=com exists in the LDAP directory. Squid uses this account only to search for the authenticating user. If the authenticating user exists, Squid binds as this user to the directory to verify the authentication.

Procedure

  1. Install the squid package: 

    # yum install squid

  2. Edit the /etc/squid/squid.conf file:

    1. To configure the basic_ldap_auth helper utility, add the following configuration entry to the top of /etc/squid/squid.conf: 

      auth_param basic program /usr/lib64/squid/basic_ldap_auth -b "cn=users,cn=accounts,dc=example,dc=com" -D "uid=proxy_user,cn=users,cn=accounts,dc=example,dc=com" -W /etc/squid/ldap_password -f "(&(objectClass=person)(uid=%s))" -ZZ -H ldap://ldap_server.example.com:389

      The following describes the parameters passed to the basic_ldap_auth helper utility in the example above:

      • -b base_DN sets the LDAP search base.
      • -D proxy_service_user_DN sets the distinguished name (DN) of the account Squid uses to search for the authenticating user in the directory.
      • -W path_to_password_file sets the path to the file that contains the password of the proxy service user. Using a password file prevents that the password is visible in the operating system’s process list.

      • -f LDAP_filter specifies the LDAP search filter. Squid replaces the %s variable with the user name provided by the authenticating user.

        The (&(objectClass=person)(uid=%s)) filter in the example defines that the user name must match the value set in the uid attribute and that the directory entry contains the person object class.

      • -ZZ enforces a TLS-encrypted connection over the LDAP protocol using the STARTTLS command. Omit the -ZZ in the following situations:

        • The LDAP server does not support encrypted connections.
        • The port specified in the URL uses the LDAPS protocol.
      • The -H LDAP_URL parameter specifies the protocol, the host name or IP address, and the port of the LDAP server in URL format.

    2. Add the following ACL and rule to configure that Squid allows only authenticated users to use the proxy: 

      acl ldap-auth proxy_auth REQUIRED
http_access allow ldap-auth
      Important

      Specify these settings before the http_access deny all rule.

    3. Remove the following rule to disable bypassing the proxy authentication from IP ranges specified in localnet ACLs: 

      http_access allow localnet

    4. The following ACL exists in the default configuration and defines 443 as a port that uses the HTTPS protocol: 

      acl SSL_ports port 443

      If users should be able to use the HTTPS protocol also on other ports, add an ACL for each of these port: 

      acl SSL_ports port port_number

    5. Update the list of acl Safe_ports rules to configure to which ports Squid can establish a connection. For example, to configure that clients using the proxy can only access resources on port 21 (FTP), 80 (HTTP), and 443 (HTTPS), keep only the following acl Safe_ports statements in the configuration: 

      acl Safe_ports port 21
acl Safe_ports port 80
acl Safe_ports port 443

      By default, the configuration contains the http_access deny !Safe_ports rule that defines access denial to ports that are not defined in Safe_ports ACLs.

    6. Configure the cache type, the path to the cache directory, the cache size, and further cache type-specific settings in the cache_dir parameter: 

      cache_dir ufs /var/spool/squid 10000 16 256

      With these settings:

      • Squid uses the ufs cache type.
      • Squid stores its cache in the /var/spool/squid/ directory.
      • The cache grows up to 10000 MB.
      • Squid creates 16 level-1 sub-directories in the /var/spool/squid/ directory.

      • Squid creates 256 sub-directories in each level-1 directory.

        If you do not set a cache_dir directive, Squid stores the cache in memory.

  3. If you set a different cache directory than /var/spool/squid/ in the cache_dir parameter:

    1. Create the cache directory: 

      # mkdir -p path_to_cache_directory

    2. Configure the permissions for the cache directory: 

      # chown squid:squid path_to_cache_directory

    3. If you run SELinux in enforcing mode, set the squid_cache_t context for the cache directory: 

      # semanage fcontext -a -t squid_cache_t "path_to_cache_directory(/.*)?"
# restorecon -Rv path_to_cache_directory

      If the semanage utility is not available on your system, install the policycoreutils-python-utils package.

  4. Store the password of the LDAP service user in the /etc/squid/ldap_password file, and set appropriate permissions for the file: 

    # echo "password" > /etc/squid/ldap_password
# chown root:squid /etc/squid/ldap_password
# chmod 640 /etc/squid/ldap_password

  5. Open the 3128 port in the firewall: 

    # firewall-cmd --permanent --add-port=3128/tcp
# firewall-cmd --reload

  6. Enable and start the squid service: 

    # systemctl enable --now squid

Verification steps

To verify that the proxy works correctly, download a web page using the curl utility: 

# curl -O -L "https://www.redhat.com/index.html" -x "user_name:password@proxy.example.com:3128"

If curl does not display any error and the index.html file was downloaded to the current directory, the proxy works.

Troubleshooting steps

To verify that the helper utility works correctly:

  1. Manually start the helper utility with the same settings you used in the auth_param parameter: 

    # /usr/lib64/squid/basic_ldap_auth -b "cn=users,cn=accounts,dc=example,dc=com" -D "uid=proxy_user,cn=users,cn=accounts,dc=example,dc=com" -W /etc/squid/ldap_password -f "(&(objectClass=person)(uid=%s))" -ZZ -H ldap://ldap_server.example.com:389

  2. Enter a valid user name and password, and press Enter: 

    user_name password

    If the helper utility returns OK, authentication succeeded.

8.3. Setting up Squid as a caching proxy with kerberos authentication

You can configure Squid as a caching proxy that authenticates users to an Active Directory (AD) using Kerberos. The procedure configures that only authenticated users can use the proxy.

Prerequisites

  • The procedure assumes that the /etc/squid/squid.conf file is as provided by the squid package. If you edited this file before, remove the file and reinstall the package.

Procedure

  1. Install the following packages: 

    # yum install squid krb5-workstation

  2. Authenticate as the AD domain administrator: 

    # kinit administrator@AD.EXAMPLE.COM

  3. Create a keytab for Squid and store it in the /etc/squid/HTTP.keytab file: 

    # export KRB5_KTNAME=FILE:/etc/squid/HTTP.keytab
# net ads keytab CREATE -U administrator

  4. Add the HTTP service principal to the keytab: 

    # net ads keytab ADD HTTP -U administrator

  5. Set the owner of the keytab file to the squid user: 

    # chown squid /etc/squid/HTTP.keytab

  6. Optionally, verify that the keytab file contains the HTTP service principal for the fully-qualified domain name (FQDN) of the proxy server: 

      klist -k /etc/squid/HTTP.keytab
Keytab name: FILE:/etc/squid/HTTP.keytab
KVNO Principal
---- ---------------------------------------------------
...
   2 HTTP/proxy.ad.example.com@AD.EXAMPLE.COM
...

  7. Edit the /etc/squid/squid.conf file:

    1. To configure the negotiate_kerberos_auth helper utility, add the following configuration entry to the top of /etc/squid/squid.conf: 

      auth_param negotiate program /usr/lib64/squid/negotiate_kerberos_auth -k /etc/squid/HTTP.keytab -s HTTP/proxy.ad.example.com@AD.EXAMPLE.COM

      The following describes the parameters passed to the negotiate_kerberos_auth helper utility in the example above:

      • -k file sets the path to the key tab file. Note that the squid user must have read permissions on this file.

      • -s HTTP/host_name@kerberos_realm sets the Kerberos principal that Squid uses.

        Optionally, you can enable logging by passing one or both of the following parameters to the helper utility:

      • -i logs informational messages, such as the authenticating user.

      • -d enables debug logging.

        Squid logs the debugging information from the helper utility to the /var/log/squid/cache.log file.

    2. Add the following ACL and rule to configure that Squid allows only authenticated users to use the proxy: 

      acl kerb-auth proxy_auth REQUIRED
http_access allow kerb-auth
      Important

      Specify these settings before the http_access deny all rule.

    3. Remove the following rule to disable bypassing the proxy authentication from IP ranges specified in localnet ACLs: 

      http_access allow localnet

    4. The following ACL exists in the default configuration and defines 443 as a port that uses the HTTPS protocol: 

      acl SSL_ports port 443

      If users should be able to use the HTTPS protocol also on other ports, add an ACL for each of these port: 

      acl SSL_ports port port_number

    5. Update the list of acl Safe_ports rules to configure to which ports Squid can establish a connection. For example, to configure that clients using the proxy can only access resources on port 21 (FTP), 80 (HTTP), and 443 (HTTPS), keep only the following acl Safe_ports statements in the configuration: 

      acl Safe_ports port 21
acl Safe_ports port 80
acl Safe_ports port 443

      By default, the configuration contains the http_access deny !Safe_ports rule that defines access denial to ports that are not defined in Safe_ports ACLs.

    6. Configure the cache type, the path to the cache directory, the cache size, and further cache type-specific settings in the cache_dir parameter: 

      cache_dir ufs /var/spool/squid 10000 16 256

      With these settings:

      • Squid uses the ufs cache type.
      • Squid stores its cache in the /var/spool/squid/ directory.
      • The cache grows up to 10000 MB.
      • Squid creates 16 level-1 sub-directories in the /var/spool/squid/ directory.

      • Squid creates 256 sub-directories in each level-1 directory.

        If you do not set a cache_dir directive, Squid stores the cache in memory.

  8. If you set a different cache directory than /var/spool/squid/ in the cache_dir parameter:

    1. Create the cache directory: 

      # mkdir -p path_to_cache_directory

    2. Configure the permissions for the cache directory: 

      # chown squid:squid path_to_cache_directory

    3. If you run SELinux in enforcing mode, set the squid_cache_t context for the cache directory: 

      # semanage fcontext -a -t squid_cache_t "path_to_cache_directory(/.*)?"
# restorecon -Rv path_to_cache_directory

      If the semanage utility is not available on your system, install the policycoreutils-python-utils package.

  9. Open the 3128 port in the firewall: 

    # firewall-cmd --permanent --add-port=3128/tcp
# firewall-cmd --reload

  10. Enable and start the squid service: 

    # systemctl enable --now squid

Verification steps

To verify that the proxy works correctly, download a web page using the curl utility: 

# curl -O -L "https://www.redhat.com/index.html" --proxy-negotiate -u : -x "proxy.ad.example.com:3128"

If curl does not display any error and the index.html file exists in the current directory, the proxy works.

Troubleshooting steps

To manually test Kerberos authentication:

  1. Obtain a Kerberos ticket for the AD account: 

    # kinit user@AD.EXAMPLE.COM

  2. Optionally, display the ticket: 

    # klist

  3. Use the negotiate_kerberos_auth_test utility to test the authentication: 

    # /usr/lib64/squid/negotiate_kerberos_auth_test proxy.ad.example.com

    If the helper utility returns a token, the authentication succeeded: 

    Token: YIIFtAYGKwYBBQUCoIIFqDC...

8.4. Configuring a domain deny list in Squid

Frequently, administrators want to block access to specific domains. This section describes how to configure a domain deny list in Squid.

Prerequisites

  • Squid is configured, and users can use the proxy.

Procedure

  1. Edit the /etc/squid/squid.conf file and add the following settings: 

    acl domain_deny_list dstdomain "/etc/squid/domain_deny_list.txt"
http_access deny all domain_deny_list
    Important

    Add these entries before the first http_access allow statement that allows access to users or clients.

  2. Create the /etc/squid/domain_deny_list.txt file and add the domains you want to block. For example, to block access to example.com including subdomains and to block example.net, add: 

    .example.com
example.net
    Important

    If you referred to the /etc/squid/domain_deny_list.txt file in the squid configuration, this file must not be empty. If the file is empty, Squid fails to start.

  3. Restart the squid service: 

    # systemctl restart squid

8.5. Configuring the Squid service to listen on a specific port or IP address

By default, the Squid proxy service listens on the 3128 port on all network interfaces. You can change the port and configuring Squid to listen on a specific IP address.

Prerequisites

  • The squid package is installed.

Procedure

  1. Edit the /etc/squid/squid.conf file:

    • To set the port on which the Squid service listens, set the port number in the http_port parameter. For example, to set the port to 8080, set: 

      http_port 8080

    • To configure on which IP address the Squid service listens, set the IP address and port number in the http_port parameter. For example, to configure that Squid listens only on the 192.0.2.1 IP address on port 3128, set: 

      http_port 192.0.2.1:3128

      Add multiple http_port parameters to the configuration file to configure that Squid listens on multiple ports and IP addresses: 

      http_port 192.0.2.1:3128
http_port 192.0.2.1:8080

  2. If you configured that Squid uses a different port as the default (3128):

    1. Open the port in the firewall: 

      # firewall-cmd --permanent --add-port=port_number/tcp
# firewall-cmd --reload

    2. If you run SELinux in enforcing mode, assign the port to the squid_port_t port type definition: 

      # semanage port -a -t squid_port_t -p tcp port_number

      If the semanage utility is not available on your system, install the policycoreutils-python-utils package.

  3. Restart the squid service: 

    # systemctl restart squid

8.6. Additional resources

  • Configuration parameters usr/share/doc/squid-<version>/squid.conf.documented

Chapter 9. Database servers

9.1. Introduction to database servers

A database server is a service that provides features of a database management system (DBMS). DBMS provides utilities for database administration and interacts with end users, applications, and databases.

Red Hat Enterprise Linux 8 provides the following database management systems:

  • MariaDB 10.3
  • MariaDB 10.5 - available since RHEL 8.4
  • MySQL 8.0
  • PostgreSQL 10
  • PostgreSQL 9.6
  • PostgreSQL 12 - available since RHEL 8.1.1
  • PostgreSQL 13 - available since RHEL 8.4

9.2. Using MariaDB

The MariaDB server is an open source fast and robust database server that is based on the MySQL technology. This part describes how to install and configure MariaDB on a RHEL system, how to back up MariaDB data, how to migrate from an earlier MariaDB version, and how to replicate a database using the MariaDB Galera Cluster.

9.2.1. Getting started with MariaDB

MariaDB is a relational database that converts data into structured information and provides an SQL interface for accessing data. It includes multiple storage engines and plug-ins, as well as geographic information system (GIS) and JavaScript Object Notation (JSON) features.

For Red Hat Enterprise Linux 8 this part describes:

9.2.2. Installing MariaDB

In RHEL 8, the MariaDB server is available in the following versions, each provided by a separate stream:

  • MariaDB 10.3
  • MariaDB 10.5 - available since RHEL 8.4

To install MariaDB, use the following procedure.

Procedure

  1. Install MariaDB server packages by selecting a stream (version) from the mariadb module and specifying the server profile. For example: 

    # yum module install mariadb:10.3/server

  2. Start the mariadb service: 

    # systemctl start mariadb.service

  3. Enable the mariadb service to start at boot: 

    # systemctl enable mariadb.service

  4. Recommended for MariaDB 10.3: To improve security when installing MariaDB, run the following command: 

    $ mysql_secure_installation

    The command launches a fully interactive script, which prompts for each step in the process. The script enables you to improve security in the following ways:

    • Setting a password for root accounts
    • Removing anonymous users

    • Disallowing remote root logins (outside the local host)

      Note

      The mysql_secure_installation script is no longer valuable in MariaDB 10.5 or later. The security enhancements are part of the default behavior since MariaDB 10.5.

Important

The MariaDB and MySQL database servers cannot be installed in parallel in RHEL 8 due to conflicting RPM packages. Parallel installation of components is possible in Red Hat Software Collections for RHEL 7. In RHEL 8, different versions of database servers can be used in containers.

9.2.3. Configuring MariaDB

To configure the MariaDB server for networking, use the following procedure.

Procedure

  1. Edit the [mysqld] section of the /etc/my.cnf.d/mariadb-server.cnf file. You can set the following configuration directives:

    • bind-address - is the address on which the server listens. Possible options are:

      • a host name
      • an IPv4 address
      • an IPv6 address

    • skip-networking - controls whether the server listens for TCP/IP connections. Possible values are:

      • 0 - to listen for all clients
      • 1 - to listen for local clients only
    • port - the port on which MariaDB listens for TCP/IP connections.

  2. Restart the mariadb service: 

    # systemctl restart mariadb.service

9.2.4. Setting up TLS encryption on a MariaDB server

By default, MariaDB uses unencrypted connections. For secure connections, enable TLS support on the MariaDB server and configure your clients to establish encrypted connections.

9.2.4.1. Placing the CA certificate, server certificate, and private key on the MariaDB server

Before you can enable TLS encryption in the MariaDB server, store the certificate authority (CA) certificate, the server certificate, and the private key on the MariaDB server.

Prerequisites

  • The following files in Privacy Enhanced Mail (PEM) format have been copied to the server:

    • The private key of the server: server.example.com.key.pem
    • The server certificate: server.example.com.crt.pem
    • The Certificate Authority (CA) certificate: ca.crt.pem

    For details about creating a private key and certificate signing request (CSR), as well as about requesting a certificate from a CA, see your CA’s documentation.

Procedure

  1. Store the CA and server certificates in the /etc/pki/tls/certs/ directory: 

    # mv <path>/server.example.com.crt.pem /etc/pki/tls/certs/
# mv <path>/ca.crt.pem /etc/pki/tls/certs/

  2. Set permissions on the CA and server certificate that enable the MariaDB server to read the files: 

    # chmod 644 /etc/pki/tls/certs/server.example.com.crt.pem /etc/pki/tls/certs/ca.crt.pem

    Because certificates are part of the communication before a secure connection is established, any client can retrieve them without authentication. Therefore, you do not need to set strict permissions on the CA and server certificate files.

  3. Store the server’s private key in the /etc/pki/tls/private/ directory: 

    # mv <path>/server.example.com.key.pem /etc/pki/tls/private/

  4. Set secure permissions on the server’s private key: 

    # chmod 640 /etc/pki/tls/private/server.example.com.key.pem
# chgrp mysql /etc/pki/tls/private/server.example.com.key.pem

    If unauthorized users have access to the private key, connections to the MariaDB server are no longer secure.

  5. Restore the SELinux context: 

    #  restorecon -Rv /etc/pki/tls/

9.2.4.2. Configuring TLS on a MariaDB server

To improve security, enable TLS support on the MariaDB server. As a result, clients can transmit data with the server using TLS encryption.

Prerequisites

  • You installed the MariaDB server.
  • The mariadb service is running.

  • The following files in Privacy Enhanced Mail (PEM) format exist on the server and are readable by the mysql user:

    • The private key of the server: /etc/pki/tls/private/server.example.com.key.pem
    • The server certificate: /etc/pki/tls/certs/server.example.com.crt.pem
    • The Certificate Authority (CA) certificate /etc/pki/tls/certs/ca.crt.pem
  • The subject distinguished name (DN) or the subject alternative name (SAN) field in the server certificate matches the server’s host name.

Procedure

  1. Create the /etc/my.cnf.d/mariadb-server-tls.cnf file:

    1. Add the following content to configure the paths to the private key, server and CA certificate: 

      [mariadb]
ssl_key = /etc/pki/tls/private/server.example.com.key.pem
ssl_cert = /etc/pki/tls/certs/server.example.com.crt.pem
ssl_ca = /etc/pki/tls/certs/ca.crt.pem

    2. If you have a Certificate Revocation List (CRL), configure the MariaDB server to use it: 

      ssl_crl = /etc/pki/tls/certs/example.crl.pem

    3. Optional: If you run MariaDB 10.5.2 or later, you can reject connection attempts without encryption. To enable this feature, append: 

      require_secure_transport = on

    4. Optional: If you run MariaDB 10.4.6 or later, you can set the TLS versions the server should support. For example, to support TLS 1.2 and TLS 1.3, append: 

      tls_version = TLSv1.2,TLSv1.3

      By default, the server supports TLS 1.1, TLS 1.2, and TLS 1.3.

  2. Restart the mariadb service: 

    # systemctl restart mariadb

Verification

To simplify troubleshooting, perform the following steps on the MariaDB server before you configure the local client to use TLS encryption:

  1. Verify that MariaDB now has TLS encryption enabled: 

    # mysql -u root -p -e "SHOW GLOBAL VARIABLES LIKE 'have_ssl';"
+---------------+-----------------+
| Variable_name | Value           |
+---------------+-----------------+
| have_ssl      | YES             |
+---------------+-----------------+

    If the have_ssl variable is set to yes, TLS encryption is enabled.

  2. If you configured the MariaDB service to only support specific TLS versions, display the tls_version variable: 

    # mysql -u root -p -e "SHOW GLOBAL VARIABLES LIKE 'tls_version';"
+---------------+-----------------+
| Variable_name | Value           |
+---------------+-----------------+
| tls_version   | TLSv1.2,TLSv1.3 |
+---------------+-----------------+

Additional resources

9.2.4.3. Requiring TLS encrypted connections for specific user accounts

Users that have access to sensitive data should always use a TLS-encrypted connection to avoid sending data unencrypted over the network.

If you cannot configure on the server that a secure transport is required for all connections (require_secure_transport = on), configure individual user accounts to require TLS encryption.

Prerequisites

  • The MariaDB server has TLS support enabled.
  • The user you configure to require secure transport exists.

Procedure

  1. Connect as an administrative user to the MariaDB server: 

    # mysql -u root -p -h server.example.com

    If your administrative user has no permissions to access the server remotely, perform the command on the MariaDB server and connect to localhost.

  2. Use the REQUIRE SSL clause to enforce that a user must connect using a TLS-encrypted connection: 

    MariaDB [(none)]> ALTER USER 'example'@'%' REQUIRE SSL;

Verification

  1. Connect to the server as the example user using TLS encryption: 

    # mysql -u example -p -h server.example.com --ssl
...
MariaDB [(none)]>

    If no error is shown and you have access to the interactive MariaDB console, the connection with TLS succeeds.

  2. Attempt to connect as the example user with TLS disabled: 

    # mysql -u example -p -h server.example.com --skip-ssl
ERROR 1045 (28000): Access denied for user 'example'@'server.example.com' (using password: YES)

    The server rejected the login attempt, because TLS is required for this user, but disabled (--skip-ssl).

Additional resources

9.2.5. Globally enabling TLS encryption in MariaDB clients

If your MariaDB server supports TLS encryption, configure your clients to establish only secure connections and to verify the server certificate. This procedure describes how to enable TLS support for all users on the server.

9.2.5.1. Configuring the MariaDB client to use TLS encryption by default

On RHEL, you can globally configure that the MariaDB client uses TLS encryption and verifies that the Common Name (CN) in the server certificate matches the hostname the user connects to. This prevents man-in-the-middle attacks.

Prerequisites

  • The MariaDB server has TLS support enabled.
  • If the certificate authority (CA) that issued the server’s certificate is not trusted by RHEL, the CA certificate has been copied to the client.

Procedure

  1. If RHEL does not trust the CA that issued the server’s certificate:

    1. Copy the CA certificate to the /etc/pki/ca-trust/source/anchors/ directory: 

      # cp <path>/ca.crt.pem /etc/pki/ca-trust/source/anchors/

    2. Set permissions that enable all users to read the CA certificate file: 

      # chmod 644 /etc/pki/ca-trust/source/anchors/ca.crt.pem

    3. Rebuild the CA trust database: 

      # update-ca-trust

  2. Create the /etc/my.cnf.d/mariadb-client-tls.cnf file with the following content: 

    [client-mariadb]
ssl
ssl-verify-server-cert

    These settings define that the MariaDB client uses TLS encryption (ssl) and that the client compares the hostname with the CN in the server certificate (ssl-verify-server-cert).

Verification

  • Connect to the server using the hostname, and display the server status: 

    # mysql -u root -p -h server.example.com -e status
...
SSL:        Cipher in use is TLS_AES_256_GCM_SHA384

    If the SSL entry contains Cipher in use is…​, the connection is encrypted.

    Note that the user you use in this command has permissions to authenticate remotely.

    If the hostname you connect to does not match the hostname in the TLS certificate of the server, the ssl-verify-server-cert parameter causes the connection to fail. For example, if you connect to localhost: 

    # mysql -u root -p -h localhost -e status
ERROR 2026 (HY000): SSL connection error: Validation of SSL server certificate failed

Additional resources

  • The --ssl* parameter descriptions in the mysql(1) man page.

9.2.6. Backing up MariaDB data

There are two main ways to back up data from a MariaDB database in Red Hat Enterprise Linux 8:

  • Logical backup
  • Physical backup

Logical backup consists of the SQL statements necessary to restore the data. This type of backup exports information and records in plain text files.

The main advantage of logical backup over physical backup is portability and flexibility. The data can be restored on other hardware configurations, MariaDB versions or Database Management System (DBMS), which is not possible with physical backups.

Note that logical backup can be performed if the mariadb.service is running. Logical backup does not include log and configuration files.

Physical backup consists of copies of files and directories that store the content.

Physical backup has the following advantages compared to logical backup:

  • Output is more compact.
  • Backup is smaller in size.
  • Backup and restore are faster.
  • Backup includes log and configuration files.

Note that physical backup must be performed when the mariadb.service is not running or all tables in the database are locked to prevent changes during the backup.

You can use one of the following MariaDB backup approaches to back up data from a MariaDB database:

  • Logical backup with mysqldump
  • Physical online backup using the Mariabackup utility
  • File system backup
  • Replication as a backup solution

9.2.6.1. Performing logical backup with mysqldump

The mysqldump client is a backup utility, which can be used to dump a database or a collection of databases for the purpose of a backup or transfer to another database server. The output of mysqldump typically consists of SQL statements to re-create the server table structure, populate it with data, or both. mysqldump can also generate files in other formats, including XML and delimited text formats, such as CSV.

To perform the mysqldump backup, you can use one of the following options:

  • Back up one or more selected databases
  • Back up all databases
  • Back up a subset of tables from one database

Procedure

  • To dump a single database, run: 

    # mysqldump [options] --databases db_name > backup-file.sql

  • To dump multiple databases at once, run: 

    # mysqldump [options] --databases db_name1 [db_name2 …​] > backup-file.sql

  • To dump all databases, run: 

    # mysqldump [options] --all-databases > backup-file.sql

  • To load one or more dumped full databases back into a server, run: 

    # mysql < backup-file.sql

  • To load a database to a remote MariaDB server, run: 

    # mysql --host=remote_host < backup-file.sql

  • To dump a subset of tables from one database, add a list of the chosen tables at the end of the mysqldump command: 

    # mysqldump [options] db_name [tbl_name …​​] > backup-file.sql

  • To load a subset of tables dumped from one database, run: 

    # mysql db_name < backup-file.sql
    Note

    The db_name database must exist at this point.

  • To see a list of the options that mysqldump supports, run: 

    $ mysqldump --help

Additional resources

9.2.6.2. Performing physical online backup using the Mariabackup utility

Mariabackup is a utility based on the Percona XtraBackup technology, which enables performing physical online backups of InnoDB, Aria, and MyISAM tables. This utility is provided by the mariadb-backup package from the AppStream repository.

Mariabackup supports full backup capability for MariaDB server, which includes encrypted and compressed data.

Prerequisites

  • The mariadb-backup package is installed on the system: 

    # yum install mariadb-backup
  • You must provide Mariabackup with credentials for the user under which the backup will be run. You can provide the credentials either on the command line or by a configuration file.
  • Users of Mariabackup must have the RELOAD, LOCK TABLES, and REPLICATION CLIENT privileges.

To create a backup of a database using Mariabackup, use the following procedure.

Procedure

  • To create a backup while providing credentials on the command line, run: 

    $ mariabackup --backup --target-dir <backup_directory> --user <backup_user> --password <backup_passwd>

    The target-dir option defines the directory where the backup files are stored. If you want to perform a full backup, the target directory must be empty or not exist.

    The user and password options allow you to configure the user name and the password.

  • To create a backup with credentials set in a configuration file:

    1. Create a configuration file in the /etc/my.cnf.d/ directory, for example, /etc/my.cnf.d/mariabackup.cnf.

    2. Add the following lines into the [xtrabackup] or [mysqld] section of the new file: 

      [xtrabackup]
user=myuser
password=mypassword

    3. Perform the backup: 

      $ mariabackup --backup --target-dir <backup_directory>
Important

Mariabackup does not read options in the [mariadb] section of configuration files. If a non-default data directory is specified on a MariaDB server, you must specify this directory in the [xtrabackup] or [mysqld] sections of configuration files so that Mariabackup is able to find the data directory.

To specify a non-default data directory, include the following line in the [xtrabackup] or [mysqld] sections of MariaDB configuration files: 

datadir=/var/mycustomdatadir

Additional resources

9.2.6.3. Restoring data using the Mariabackup utility

When the backup is complete, you can restore the data from the backup by using the mariabackup command with one of the following options:

  • --copy-back allows you to keep the original backup files.
  • --move-back moves the backup files to the data directory and removes the original backup files.

To restore data using the Mariabackup utility, use the following procedure.

Prerequisites

  • Verify that the mariadb service is not running: 

    # systemctl stop mariadb.service
  • Verify that the data directory is empty.
  • Users of Mariabackup must have the RELOAD, LOCK TABLES, and REPLICATION CLIENT privileges.

Procedure

  1. Run the mariabackup command:

    • To restore data and keep the original backup files, use the --copy-back option: 

      $ mariabackup --copy-back --target-dir=/var/mariadb/backup/

    • To restore data and remove the original backup files, use the --move-back option: 

      $ mariabackup --move-back --target-dir=/var/mariadb/backup/

  2. Fix the file permissions.

    When restoring a database, Mariabackup preserves the file and directory privileges of the backup. However, Mariabackup writes the files to disk as the user and group restoring the database. After restoring a backup, you may need to adjust the owner of the data directory to match the user and group for the MariaDB server, typically mysql for both.

    For example, to recursively change ownership of the files to the mysql user and group: 

    # chown -R mysql:mysql /var/lib/mysql/

  3. Start the mariadb service: 

    # systemctl start mariadb.service

Additional resources

9.2.6.4. Performing file system backup

To create a file system backup of MariaDB data files, copy the content of the MariaDB data directory to your backup location.

To back up also your current configuration or the log files, use the optional steps of the following procedure.

Procedure

  1. Stop the mariadb service: 

    # systemctl stop mariadb.service

  2. Copy the data files to the required location: 

    # cp -r /var/lib/mysql /backup-location

  3. Optionally, copy the configuration files to the required location: 

    # cp -r /etc/my.cnf /etc/my.cnf.d /backup-location/configuration

  4. Optionally, copy the log files to the required location: 

    # cp /var/log/mariadb/ /backup-location/logs*

  5. Start the mariadb service: 

    # systemctl start mariadb.service

  6. When loading the backed up data from the backup location to the /var/lib/mysql directory, ensure that mysql:mysql is an owner of all data in /var/lib/mysql: 

    # chown -R mysql:mysql /var/lib/mysql

9.2.6.5. Replication as a backup solution

Replication is an alternative backup solution for source servers. If a source server replicates to a replica server, backups can be run on the replica without any impact on the source. The source can still run while you shut down the replica and back the data up from the replica.

Warning

Replication itself is not a sufficient backup solution. Replication protects source servers against hardware failures, but it does not ensure protection against data loss. It is recommended that you use any other backup solution on the replica together with this method.

Additional resources

9.2.7. Migrating to MariaDB 10.3

RHEL 7 contains MariaDB 5.5 as the default implementation of a server from the MySQL databases family. Later versions of the MariaDB database server are available as Software Collections for RHEL 7. RHEL 8 provides MariaDB 10.3, MariaDB 10.5, and MySQL 8.0.

This part describes migration to MariaDB 10.3 from a RHEL 7 or Red Hat Software Collections version of MariaDB. If you want to migrate from MariaDB 10.3 to MariaDB 10.5 within RHEL 8, see Upgrading from MariaDB 10.3 to MariaDB 10.5 instead.

9.2.7.1. Notable differences between the RHEL 7 and RHEL 8 versions of MariaDB

The most important changes between MariaDB 5.5 and MariaDB 10.3 are as follows:

  • MariaDB Galera Cluster, a synchronous multi-source cluster, is a standard part of MariaDB since 10.1.
  • The ARCHIVE storage engine is no longer enabled by default, and the plug-in needs to be specifically enabled.
  • The BLACKHOLE storage engine is no longer enabled by default, and the plug-in needs to be specifically enabled.

  • InnoDB is used as the default storage engine instead of XtraDB, which was used in MariaDB 10.1 and earlier versions.

    For more details, see Why does MariaDB 10.2 use InnoDB instead of XtraDB?.

  • The new mariadb-connector-c packages provide a common client library for MySQL and MariaDB. This library is usable with any version of the MySQL and MariaDB database servers. As a result, the user is able to connect one build of an application to any of the MySQL and MariaDB servers distributed with Red Hat Enterprise Linux 8.

To migrate from MariaDB 5.5 to MariaDB 10.3, you need to perform multiple configuration changes as described in Migrating to MariaDB.

9.2.7.2. Configuration changes

The recommended migration path from MariaDB 5.5 to MariaDB 10.3 is to upgrade to MariaDB 10.0 first, and then upgrade by one version successively.

The main advantage of upgrading one minor version at a time is better adaptation of the database, including both data and configuration, to the changes. The upgrade ends on the same major version as is available in RHEL 8 (MariaDB 10.3), which significantly reduces configuration changes or other issues.

For more information about configuration changes when migrating from MariaDB 5.5 to MariaDB 10.0, see Migrating to MariaDB 10.0 in Red Hat Software Collections documentation.

The migration to following successive versions of MariaDB and the required configuration changes is described in these documents:

Note

Migration directly from MariaDB 5.5 to MariaDB 10.3 is also possible, but you must perform all configuration changes that are required by differences described in the migration documents above.

9.2.7.3. In-place upgrade using the mysql_upgrade utility

To migrate the database files to RHEL 8, users of MariaDB on RHEL 7 must perform the in-place upgrade using the mysql_upgrade utility. The mysql_upgrade utility is provided by the mariadb-server-utils subpackage, which is installed as a dependency of the mariadb-server package.

To perform an in-place upgrade, you must copy binary data files to the /var/lib/mysql/ data directory on the RHEL 8 system and use the mysql_upgrade utility.

You can use this method for migrating data from:

  • The Red Hat Enterprise Linux 7 version of MariaDB 5.5

  • The Red Hat Software Collections versions of:

    • MariaDB 5.5 (no longer supported)
    • MariaDB 10.0 (no longer supported)
    • MariaDB 10.1 (no longer supported)
    • MariaDB 10.2 (no longer supported)

    • MariaDB 10.3

      Note that it is recommended to upgrade to MariaDB 10.3 by one version successively. See the respective Migration chapters in the Release Notes for Red Hat Software Collections.

Note

If you are upgrading from the RHEL 7 version of MariaDB, the source data is stored in the /var/lib/mysql/ directory. In case of Red Hat Software Collections versions of MariaDB, the source data directory is /var/opt/rh/<collection_name>/lib/mysql/ (with the exception of the mariadb55, which uses the /opt/rh/mariadb55/root/var/lib/mysql/ data directory).

To perform an upgrade using the mysql_upgrade utility, use the following procedure.

Prerequisites

  • Before performing the upgrade, back up all your data stored in the MariaDB databases.

Procedure

  1. Ensure that the mariadb-server package is installed on the RHEL 8 system: 

    # yum install mariadb-server

  2. Ensure that the mariadb service is not running on either of the source and target systems at the time of copying data: 

    # systemctl stop mariadb.service
  3. Copy the data from the source location to the /var/lib/mysql/ directory on the RHEL 8 target system.

  4. Set the appropriate permissions and SELinux context for copied files on the target system: 

    # restorecon -vr /var/lib/mysql

  5. Start the MariaDB server on the target system: 

    # systemctl start mariadb.service

  6. Run the mysql_upgrade command to check and repair internal tables: 

    $ mysql_upgrade
  7. When the upgrade is complete, verify that all configuration files within the /etc/my.cnf.d/ directory include only options valid for MariaDB 10.3.
Important

There are certain risks and known problems related to an in-place upgrade. For example, some queries might not work or they will be run in different order than before the upgrade. For more information about these risks and problems, and for general information about an in-place upgrade, see MariaDB 10.3 Release Notes.

9.2.8. Upgrading from MariaDB 10.3 to MariaDB 10.5

This part describes migration from MariaDB 10.3 to MariaDB 10.5 within RHEL 8.

9.2.8.1. Notable differences between MariaDB 10.3 and MariaDB 10.5

Significant changes between MariaDB 10.3 and MariaDB 10.5 include:

  • MariaDB now uses the unix_socket authentication plug-in by default. The plug-in enables users to use operating system credentials when connecting to MariaDB through the local UNIX socket file.
  • MariaDB adds mariadb-* named binaries and mysql* symbolic links pointing to the mariadb-* binaires. For example, the mysqladmin, mysqlaccess, and mysqlshow symlinks point to the mariadb-admin, mariadb-access, and mariadb-show binaries, respectively.
  • The SUPER privilege has been split into several privileges to better align with each user role. As a result, certain statements have changed required privileges.
  • In parallel replication, the slave_parallel_mode now defaults to optimistic.
  • In the InnoDB storage engine, defaults of the following variables have been changed: innodb_adaptive_hash_index to OFF and innodb_checksum_algorithm to full_crc32.

  • MariaDB now uses the libedit implementation of the underlying software managing the MariaDB command history (the .mysql_history file) instead of the previously used readline library. This change impacts users working directly with the .mysql_history file. Note that .mysql_history is a file managed by the MariaDB or MySQL applications, and users should not work with the file directly. The human-readable appearance is coincidental.

    Note

    To increase security, you can consider not maintaining a history file. To disable the command history recording:

    1. Remove the .mysql_history file if it exists.

    2. Use either of the following approaches:

      • Set the MYSQL_HISTFILE variable to /dev/null and include this setting in any of your shell’s startup files.

      • Change the .mysql_history file to a symbolic link to /dev/null: 

        $ ln -s /dev/null $HOME/.mysql_history

MariaDB Galera Cluster has been upgraded to version 4 with the following notable changes:

  • Galera adds a new streaming replication feature, which supports replicating transactions of unlimited size. During an execution of streaming replication, a cluster replicates a transaction in small fragments.
  • Galera now fully supports Global Transaction ID (GTID).
  • The default value for the wsrep_on option in the /etc/my.cnf.d/galera.cnf file has changed from 1 to 0 to prevent end users from starting wsrep replication without configuring required additional options.

Changes to the PAM plug-in in MariaDB 10.5 include:

  • MariaDB 10.5 adds a new version of the Pluggable Authentication Modules (PAM) plug-in. The PAM plug-in version 2.0 performs PAM authentication using a separate setuid root helper binary, which enables MariaDB to use additional PAM modules.
  • The helper binary can be executed only by users in the mysql group. By default, the group contains only the mysql user. Red Hat recommends that administrators do not add more users to the mysql group to prevent password-guessing attacks without throttling or logging through this helper utility.
  • In MariaDB 10.5, the Pluggable Authentication Modules (PAM) plug-in and its related files have been moved to a new package, mariadb-pam. As a result, no new setuid root binary is introduced on systems that do not use PAM authentication for MariaDB.
  • The mariadb-pam package contains both PAM plug-in versions: version 2.0 is the default, and version 1.0 is available as the auth_pam_v1 shared object library.
  • The mariadb-pam package is not installed by default with the MariaDB server. To make the PAM authentication plug-in available in MariaDB 10.5, install the mariadb-pam package manually.

9.2.8.2. Upgrading from a RHEL 8 version of MariaDB 10.3 to MariaDB 10.5

This procedure describes upgrading from the mariadb:10.3 module stream to the mariadb:10.5 module stream using the yum and mariadb-upgrade utilities.

The mariadb-upgrade utility is provided by the mariadb-server-utils subpackage, which is installed as a dependency of the mariadb-server package.

Prerequisites

  • Before performing the upgrade, back up all your data stored in the MariaDB databases.

Procedure

  1. Stop the MariaDB server: 

    # systemctl stop mariadb.service

  2. Execute the following command to determine if your system is prepared for switching to a later stream: 

    # yum distro-sync

    This command must finish with the message Nothing to do. Complete! For more information, see Switching to a later stream.

  3. Reset the mariadb module on your system: 

    # yum module reset mariadb

  4. Enable the new mariadb:10.5 module stream: 

    # yum module enable mariadb:10.5

  5. Synchronize installed packages to perform the change between streams: 

    # yum distro-sync

    This will update all installed MariaDB packages.

  6. Adjust configuration so that option files located in /etc/my.cnf.d/ include only options valid for MariaDB 10.5. For details, see upstream documentation for MariaDB 10.4 and MariaDB 10.5.

  7. Start the MariaDB server.

    • When upgrading a database running standalone: 

      # systemctl start mariadb.service

    • When upgrading a Galera cluster node: 

      # galera_new_cluster

      The mariadb service will be started automatically.

  8. Execute the mariadb-upgrade utility to check and repair internal tables.

    • When upgrading a database running standalone: 

      # mariadb-upgrade

    • When upgrading a Galera cluster node: 

      # mariadb-upgrade --skip-write-binlog
Important

There are certain risks and known problems related to an in-place upgrade. For example, some queries might not work or they will be run in different order than before the upgrade. For more information about these risks and problems, and for general information about an in-place upgrade, see MariaDB 10.5 Release Notes.

9.2.9. Replicating MariaDB with Galera

This section describes how to replicate a MariaDB database using the Galera solution on Red Hat Enterprise Linux 8.

9.2.9.1. Introduction to MariaDB Galera Cluster

Galera replication is based on the creation of a synchronous multi-source MariaDB Galera Cluster consisting of multiple MariaDB servers. Unlike the traditional primary/replica setup where replicas are usually read-only, nodes in the MariaDB Galera Cluster can be all writable.

The interface between Galera replication and a MariaDB database is defined by the write set replication API (wsrep API).

The main features of MariaDB Galera Cluster are:

  • Synchronous replication
  • Active-active multi-source topology
  • Read and write to any cluster node
  • Automatic membership control, failed nodes drop from the cluster
  • Automatic node joining
  • Parallel replication on row level
  • Direct client connections: users can log on to the cluster nodes, and work with the nodes directly while the replication runs

Synchronous replication means that a server replicates a transaction at commit time by broadcasting the write set associated with the transaction to every node in the cluster. The client (user application) connects directly to the Database Management System (DBMS), and experiences behavior that is similar to native MariaDB.

Synchronous replication guarantees that a change that happened on one node in the cluster happens on other nodes in the cluster at the same time.

Therefore, synchronous replication has the following advantages over asynchronous replication:

  • No delay in propagation of the changes between particular cluster nodes
  • All cluster nodes are always consistent
  • The latest changes are not lost if one of the cluster nodes crashes
  • Transactions on all cluster nodes are executed in parallel
  • Causality across the whole cluster

Additional resources

9.2.9.2. Components to build MariaDB Galera Cluster

To build MariaDB Galera Cluster, you must install the following packages on your system:

  • mariadb-server-galera - contains support files and scripts for MariaDB Galera Cluster.
  • mariadb-server - is patched by MariaDB upstream to include the write set replication API (wsrep API). This API provides the interface between Galera replication and MariaDB.

  • galera - is patched by MariaDB upstream to add full support for MariaDB. The galera package contains the following:

    • Galera Replication Library provides the whole replication functionality.
    • The Galera Arbitrator utility can be used as a cluster member that participates in voting in split-brain scenarios. However, Galera Arbitrator cannot participate in the actual replication.
    • Galera Systemd service and Galera wrapper script which are used for deploying the Galera Arbitrator utility. MariaDB 10.3 and MariaDB 10.5 in RHEL 8 include a Red Hat version of the garbd systemd service and a wrapper script for the galera package in the /usr/lib/systemd/system/garbd.service and /usr/sbin/garbd-wrapper files, respectively. Since RHEL 8.6, MariaDB 10.3 and MariaDB 10.5 now also provide an upstream version of these files located at /usr/share/doc/galera/garb-systemd and /usr/share/doc/galera/garbd.service.

Additional resources

9.2.9.3. Deploying MariaDB Galera Cluster

Prerequisites

  • Install MariaDB Galera Cluster packages by selecting a stream (version) from the mariadb module and specifying the galera profile. For example: 

    # yum module install mariadb:10.3/galera

    As a result, the following packages are installed:

    • mariadb-server-galera
    • mariadb-server

    • galera

      The mariadb-server-galera package pulls the mariadb-server and galera packages as its dependency.

      For more information about which packages you need to install to build MariaDB Galera Cluster, see Components to build MariaDB Cluster.

  • The MariaDB server replication configuration must be updated before the system is added to a cluster for the first time.

    The default configuration is distributed in the /etc/my.cnf.d/galera.cnf file.

    Before deploying MariaDB Galera Cluster, set the wsrep_cluster_address option in the /etc/my.cnf.d/galera.cnf file on all nodes to start with the following string: 

    gcomm://

    • For the initial node, it is possible to set wsrep_cluster_address as an empty list: 

      wsrep_cluster_address="gcomm://"

    • For all other nodes, set wsrep_cluster_address to include an address to any node which is already a part of the running cluster. For example: 

      wsrep_cluster_address="gcomm://10.0.0.10"

      For more information about how to set Galera Cluster address, see Galera Cluster Address.

Procedure

  1. Bootstrap a first node of a new cluster by running the following wrapper on that node: 

    # galera_new_cluster

    This wrapper ensures that the MariaDB server daemon (mysqld) runs with the --wsrep-new-cluster option. This option provides the information that there is no existing cluster to connect to. Therefore, the node creates a new UUID to identify the new cluster.

    Note

    The mariadb service supports a systemd method for interacting with multiple MariaDB server processes. Therefore, in cases with multiple running MariaDB servers, you can bootstrap a specific instance by specifying the instance name as a suffix: 

    # galera_new_cluster mariadb@node1

  2. Connect other nodes to the cluster by running the following command on each of the nodes: 

    # systemctl start mariadb

    As a result, the node connects to the cluster, and synchronizes itself with the state of the cluster.

Additional resources

9.2.9.4. Adding a new node to MariaDB Galera Cluster

To add a new node to MariaDB Galera Cluster, use the following procedure.

Note that you can also use this procedure to reconnect an already existing node.

Procedure

  • On the particular node, provide an address to one or more existing cluster members in the wsrep_cluster_address option within the [mariadb] section of the /etc/my.cnf.d/galera.cnf configuration file : 

    [mariadb]
wsrep_cluster_address="gcomm://192.168.0.1"

    When a new node connects to one of the existing cluster nodes, it is able to see all nodes in the cluster.

    However, preferably list all nodes of the cluster in wsrep_cluster_address.

    As a result, any node can join a cluster by connecting to any other cluster node, even if one or more cluster nodes are down. When all members agree on the membership, the cluster’s state is changed. If the new node’s state is different from the state of the cluster, the new node requests either an Incremental State Transfer (IST) or a State Snapshot Transfer (SST) to ensure consistency with the other nodes.

Additional resources

9.2.9.5. Restarting MariaDB Galera Cluster

If you shut down all nodes at the same time, you stop the cluster, and the running cluster no longer exists. However, the cluster’s data still exist.

To restart the cluster, bootstrap a first node as described in Configuring MariaDB Galera Cluster.

Warning

If the cluster is not bootstrapped, and mysqld on the first node is started with only the systemctl start mariadb command, the node tries to connect to at least one of the nodes listed in the wsrep_cluster_address option in the /etc/my.cnf.d/galera.cnf file. If no nodes are currently running, the restart fails.

Additional resources

9.3. Using MySQL

The MySQL server is an open source fast and robust database server. This part describes how to install and configure MySQL on a RHEL system, how to back up MySQL data, how to migrate from an earlier MySQL version, and how to replicate a MySQL.

9.3.1. Getting started with MySQL

MySQL is a relational database that converts data into structured information and provides an SQL interface for accessing data. It includes multiple storage engines and plug-ins, as well as geographic information system (GIS) and JavaScript Object Notation (JSON) features.

This part describes:

9.3.2. Installing MySQL

In RHEL 8, the MySQL 8.0 server is available as the mysql:8.0 module stream.

To install MySQL, use the following procedure.

Procedure

  1. Install MySQL server packages by selecting the 8.0 stream (version) from the mysql module and specifying the server profile: 

    # yum module install mysql:8.0/server

  2. Start the mysqld service: 

    # systemctl start mysqld.service

  3. Enable the mysqld service to start at boot: 

    # systemctl enable mysqld.service

  4. Recommended: To improve security when installing MySQL, run the following command: 

    $ mysql_secure_installation

    The command launches a fully interactive script, which prompts for each step in the process. The script enables you to improve security in the following ways:

    • Setting a password for root accounts
    • Removing anonymous users
    • Disallowing remote root logins (outside the local host)
Note

The MySQL and MariaDB database servers cannot be installed in parallel in RHEL 8 due to conflicting RPM packages. Parallel installation of components is possible in Red Hat Software Collections for RHEL 7. In RHEL 8, different versions of database servers can be used in containers.

9.3.3. Configuring MySQL

To configure the MySQL server for networking, use the following procedure.

Procedure

  1. Edit the [mysqld] section of the /etc/my.cnf.d/mysql-server.cnf file. You can set the following configuration directives:

    • bind-address - is the address on which the server listens. Possible options are:

      • a host name
      • an IPv4 address
      • an IPv6 address

    • skip-networking - controls whether the server listens for TCP/IP connections. Possible values are:

      • 0 - to listen for all clients
      • 1 - to listen for local clients only
    • port - the port on which MySQL listens for TCP/IP connections.

  2. Restart the mysqld service: 

    # systemctl restart mysqld.service

9.3.4. Backing up MySQL data

There are two main ways to back up data from a MySQL database in Red Hat Enterprise Linux 8:

  • Logical backup
  • Physical backup

Logical backup consists of the SQL statements necessary to restore the data. This type of backup exports information and records in plain text files.

The main advantage of logical backup over physical backup is portability and flexibility. The data can be restored on other hardware configurations, MySQL versions or Database Management System (DBMS), which is not possible with physical backups.

Note that logical backup can be performed if the mysqld.service is running. Logical backup does not include log and configuration files.

Physical backup consists of copies of files and directories that store the content.

Physical backup has the following advantages compared to logical backup:

  • Output is more compact.
  • Backup is smaller in size.
  • Backup and restore are faster.
  • Backup includes log and configuration files.

Note that physical backup must be performed when the mysqld.service is not running or all tables in the database are locked to prevent changes during the backup.

You can use one of the following MySQL backup approaches to back up data from a MySQL database:

  • Logical backup with mysqldump
  • File system backup
  • Replication as a backup solution

9.3.4.1. Performing logical backup with mysqldump

The mysqldump client is a backup utility, which can be used to dump a database or a collection of databases for the purpose of a backup or transfer to another database server. The output of mysqldump typically consists of SQL statements to re-create the server table structure, populate it with data, or both. mysqldump can also generate files in other formats, including XML and delimited text formats, such as CSV.

To perform the mysqldump backup, you can use one of the following options:

  • Back up one or more selected databases
  • Back up all databases
  • Back up a subset of tables from one database

Procedure

  • To dump a single database, run: 

    # mysqldump [options] --databases db_name > backup-file.sql

  • To dump multiple databases at once, run: 

    # mysqldump [options] --databases db_name1 [db_name2 ...] > backup-file.sql

  • To dump all databases, run: 

    # mysqldump [options] --all-databases > backup-file.sql

  • To load one or more dumped full databases back into a server, run: 

    # mysql < backup-file.sql

  • To load a database to a remote MySQL server, run: 

    # mysql --host=remote_host < backup-file.sql

  • To dump a subset of tables from one database, add a list of the chosen tables at the end of the mysqldump command: 

    # mysqldump [options] db_name [tbl_name ...​] > backup-file.sql

  • To load a subset of tables dumped from one database, run: 

    # mysql db_name < backup-file.sql
    Note

    The db_name database must exist at this point.

  • To see a list of the options that mysqldump supports, run: 

    $ mysqldump --help

Additional resources

9.3.4.2. Performing file system backup

To create a file system backup of MySQL data files, copy the content of the MySQL data directory to your backup location.

To back up also your current configuration or the log files, use the optional steps of the following procedure.

Procedure

  1. Stop the mysqld service: 

    # systemctl stop mysqld.service

  2. Copy the data files to the required location: 

    # cp -r /var/lib/mysql /backup-location

  3. Optionally, copy the configuration files to the required location: 

    # cp -r /etc/my.cnf /etc/my.cnf.d /backup-location/configuration

  4. Optionally, copy the log files to the required location: 

    # cp /var/log/mysql/* /backup-location/logs

  5. Start the mysqld service: 

    # systemctl start mysqld.service

  6. When loading the backed up data from the backup location to the /var/lib/mysql directory, ensure that mysql:mysql is an owner of all data in /var/lib/mysql: 

    # chown -R mysql:mysql /var/lib/mysql

9.3.4.3. Replication as a backup solution

Replication is an alternative backup solution for source servers. If a source server replicates to a replica server, backups can be run on the replica without any impact on the source. The source can still run while you shut down the replica and back the data up from the replica.

For instructions on how to replicate a MySQL database, see Replicating MySQL.

Warning

Replication itself is not a sufficient backup solution. Replication protects source servers against hardware failures, but it does not ensure protection against data loss. It is recommended that you use any other backup solution on the replica together with this method.

Additional resources

9.3.5. Migrating to a RHEL 8 version of MySQL 8.0

RHEL 7 contains MariaDB 5.5 as the default implementation of a server from the MySQL databases family. The Red Hat Software Collections offering for RHEL 7 provides MySQL 8.0 and several versions of MariaDB. RHEL 8 provides MySQL 8.0, MariaDB 10.3, and MariaDB 10.5.

This procedure describes migration from a Red Hat Software Collections version of MySQL 8.0 to a RHEL 8 version of MySQL 8.0 using the mysql_upgrade utility. The mysql_upgrade utility is provided by the mysql-server package.

Note

In the Red Hat Software Collections version of MySQL, the source data directory is /var/opt/rh/rh-mysql80/lib/mysql/. In RHEL 8, MySQL data is stored in the /var/lib/mysql/ directory.

Prerequisites

  • Before performing the upgrade, back up all your data stored in the MySQL databases.

Procedure

  1. Ensure that the mysql-server package is installed on the RHEL 8 system: 

    # yum install mysql-server

  2. Ensure that the mysqld service is not running on either of the source and target systems at the time of copying data: 

    # systemctl stop mysqld.service
  3. Copy the data from the /var/opt/rh/rh-mysql80/lib/mysql/ directory on the RHEL 7 source system to the /var/lib/mysql/ directory on the RHEL 8 target system.

  4. Set the appropriate permissions and SELinux context for copied files on the target system: 

    # restorecon -vr /var/lib/mysql

  5. Ensure that mysql:mysql is an owner of all data in the /var/lib/mysql directory: 

    # chown -R mysql:mysql /var/lib/mysql

  6. Start the MySQL server on the target system: 

    # systemctl start mysqld.service

    Note: In earlier versions of MySQL, the mysql_upgrade command was needed to check and repair internal tables. This is now done automatically when you start the server.

9.3.6. Replicating MySQL

MySQL provides various configuration options for replication, ranging from basic to advanced. This section describes a transaction-based way to replicate in MySQL on freshly installed MySQL servers using global transaction identifiers (GTIDs). Using GTIDs simplifies transaction identification and consistency verification.

To set up replication in MySQL, you must:

Important

If you want to use existing MySQL servers for replication, you must first synchronize data. See the upstream documentation for more information.

9.3.6.1. Configuring a MySQL source server

You can set configuration options required for a MySQL source server to properly run and replicate all changes made on the database server.

Prerequisites

  • The source server is installed.

Procedure

  1. Include the following options in the /etc/my.cnf.d/mysql-server.cnf file under the [mysqld] section:

    • bind-address=source_ip_adress

      This option is required for connections made from replicas to the source.

    • server-id=id

      The id must be unique.

    • log_bin=path_to_source_server_log

      This option defines a path to the binary log file of the MySQL source server. For example: log_bin=/var/log/mysql/mysql-bin.log.

    • gtid_mode=ON

      This option enables global transaction identifiers (GTIDs) on the server.

    • enforce-gtid-consistency=ON

      The server enforces GTID consistency by allowing execution of only statements that can be safely logged using a GTID.

    • Optional: binlog_do_db=db_name

      Use this option if you want to replicate only selected databases. To replicate more than one selected database, specify each of the databases separately: 

      binlog_do_db=db_name1
binlog_do_db=db_name2
binlog_do_db=db_name3

    • Optional: binlog_ignore_db=db_name

      Use this option to exclude a specific database from replication.

  2. Restart the mysqld service: 

    # systemctl restart mysqld.service

9.3.6.2. Configuring a MySQL replica server

You can set configuration options required for a MySQL replica server to ensure a successful replication.

Prerequisites

  • The replica server is installed.

Procedure

  1. Include the following options in the /etc/my.cnf.d/mysql-server.cnf file under the [mysqld] section:

    • server-id=id

      The id must be unique.

    • relay-log=path_to_replica_server_log

      The relay log is a set of log files created by the MySQL replica server during replication.

    • log_bin=path_to_replica_sever_log

      This option defines a path to the binary log file of the MySQL replica server. For example: log_bin=/var/log/mysql/mysql-bin.log.

      This option is not required in a replica but strongly recommended.

    • gtid_mode=ON

      This option enables global transaction identifiers (GTIDs) on the server.

    • enforce-gtid-consistency=ON

      The server enforces GTID consistency by allowing execution of only statements that can be safely logged using a GTID.

    • log-replica-updates=ON

      This option ensures that updates received from the source server are logged in the replica’s binary log.

    • skip-replica-start=ON

      This option ensures that the replica server does not start the replication threads when the replica server starts.

    • Optional: binlog_do_db=db_name

      Use this option if you want to replicate only certain databases. To replicate more than one database, specify each of the databases separately: 

      binlog_do_db=db_name1
binlog_do_db=db_name2
binlog_do_db=db_name3

    • Optional: binlog_ignore_db=db_name

      Use this option to exclude a specific database from replication.

  2. Restart the mysqld service: 

    # systemctl restart mysqld.service

9.3.6.3. Creating a replication user on the MySQL source server

You must create a replication user and grant this user permissions required for replication traffic. This procedure shows how to create a replication user with appropriate permissions. Execute these steps only on the source server.

Prerequisites

Procedure

  1. Create a replication user: 

    mysql> CREATE USER 'replication_user'@'replica_server_ip' IDENTIFIED WITH mysql_native_password BY 'password';

  2. Grant the user replication permissions: 

    mysql> GRANT REPLICATION SLAVE ON *.* TO 'replication_user'@'replica_server_ip';

  3. Reload the grant tables in the MySQL database: 

    mysql> FLUSH PRIVILEGES;

  4. Set the source server to read-only state: 

    mysql> SET @@GLOBAL.read_only = ON;

9.3.6.4. Connecting the replica server to the source server

On the MySQL replica server, you must configure credentials and the address of the source server. Use the following procedure to implement the replica server.

Prerequisites

Procedure

  1. Set the replica server to read-only state: 

    mysql> SET @@GLOBAL.read_only = ON;

  2. Configure the replication source: 

    mysql> CHANGE REPLICATION SOURCE TO
    -> SOURCE_HOST='source_ip_address',
    -> SOURCE_USER='replication_user',
    -> SOURCE_PASSWORD='password',
    -> SOURCE_AUTO_POSITION=1;

  3. Start the replica thread in the MySQL replica server: 

    mysql> START REPLICA;

  4. Unset the read-only state on both the source and replica servers: 

    mysql> SET @@GLOBAL.read_only = OFF;

  5. Optional: Inspect the status of the replica server for debugging purposes: 

    mysql> SHOW REPLICA STATUS\G;
    Note

    If the replica server fails to start or connect, you can skip a certain number of events following the binary log file position displayed in the output of the SHOW MASTER STATUS command. For example, skip the first event from the defined position: 

    mysql> SET GLOBAL SQL_SLAVE_SKIP_COUNTER=1;

    and try to start the replica server again.

  6. Optional: Stop the replica thread in the replica server: 

    mysql> STOP REPLICA;

9.3.6.5. Verification steps

  1. Create an example database on the source server: 

    mysql> CREATE DATABASE test_db_name;
  2. Verify that the test_db_name database replicates on the replica server.

  3. Display status information about the binary log files of the MySQL server by executing the following command on either of the source or replica servers: 

    mysql> SHOW MASTER STATUS;

    The Executed_Gtid_Set column, which shows a set of GTIDs for transactions executed on the source, must not be empty.

    Note

    The same set of GTIDs is displayed in the Executed_Gtid_Set row when you use the SHOW SLAVE STATUS on the replica server.

9.3.6.6. Additional resources

9.4. Using PostgreSQL

The PostgreSQL server is an open source robust and highly-extensible database server based on the SQL language. This part describes how to install and configure PostgreSQL on a RHEL system, how to back up PostgreSQL data, and how to migrate from an earlier PostgreSQL version

9.4.1. Getting started with PostgreSQL

The PostgreSQL server provides an object-relational database system, which allows you to manage extensive datasets and a high number of concurrent users. For these reasons, the PostgreSQL servers can be used in clusters to manage high amounts of data.

The PostgreSQL server includes features for ensuring data integrity, building fault-tolerant environments, and building applications. It allows users to extend a database with users' own data types, custom functions, or code from different programming languages without the need to recompile the database.

This part describes:

9.4.2. Installing PostgreSQL

In RHEL 8, the PostgreSQL server is available in several versions, each provided by a separate stream:

  • PostgreSQL 10 - the default stream
  • PostgreSQL 9.6
  • PostgreSQL 12 - available since RHEL 8.1.1
  • PostgreSQL 13 - available since RHEL 8.4
  • PostgreSQL 15 - available since RHEL 8.8
Note

By design, it is impossible to install more than one version (stream) of the same module in parallel. Thus you must choose only one of the available streams from the postgresql module. Parallel installation of components is possible in Red Hat Software Collections for RHEL 7. In RHEL 8, different versions of database servers can be used in containers.

To install PostgreSQL, use the following procedure.

Procedure

  1. Install the PostgreSQL server packages by selecting a stream (version) from the postgresql module and specifying the server profile. For example: 

    # yum module install postgresql:15/server

    The postgres superuser is created automatically.

  2. Initialize the database cluster: 

    # postgresql-setup --initdb

    Red Hat recommends storing the data in the default /var/lib/pgsql/data directory.

  3. Start the postgresql service: 

    # systemctl start postgresql.service

  4. Enable the postgresql service to start at boot: 

    # systemctl enable postgresql.service

For information about using module streams, see Installing, managing, and removing user-space components.

Important

If you want to upgrade from an earlier postgresql stream within RHEL 8, follow both procedures described in Switching to a later stream and in Section 9.4.7, “Migrating to a RHEL 8 version of PostgreSQL”.

9.4.3. Creating PostgreSQL users

PostgreSQL users are of the following types:

  • The postgres UNIX system user - should be used only to run the PostgreSQL server and client applications, such as pg_dump. Do not use the postgres system user for any interactive work on PostgreSQL administration, such as database creation and user management.
  • A database superuser - the default postgres PostgreSQL superuser is not related to the postgres system user. You can limit access of the postgres superuser in the pg_hba.conf file, otherwise no other permission limitations exist. You can also create other database superusers.

  • A role with specific database access permissions:

    • A database user - has a permission to log in by default
    • A group of users - enables managing permissions for the group as a whole

Roles can own database objects (for example, tables and functions) and can assign object privileges to other roles using SQL commands.

Standard database management privileges include SELECT, INSERT, UPDATE, DELETE, TRUNCATE, REFERENCES, TRIGGER, CREATE, CONNECT, TEMPORARY, EXECUTE, and USAGE.

Role attributes are special privileges, such as LOGIN, SUPERUSER, CREATEDB, and CREATEROLE.

Important

Red Hat recommends performing most tasks as a role that is not a superuser. A common practice is to create a role that has the CREATEDB and CREATEROLE privileges and use this role for all routine management of databases and roles.

Prerequisites

  • The PostgreSQL server is installed.
  • The database cluster is initialized.

Procedure

  • To create a user, set a password for the user, and assign the user the CREATEROLE and CREATEDB permissions: 

    postgres=# CREATE USER mydbuser WITH PASSWORD 'mypasswd' CREATEROLE CREATEDB;

    Replace mydbuser with the username and mypasswd with the user’s password.

Additional resources

Example 9.1. Initializing, creating, and connecting to a PostgreSQL database

This example demonstrates how to initialize a PostgreSQL database, create a database user with routine database management privileges, and how to create a database that is accessible from any system account through the database user with management privileges.

  1. Install the PosgreSQL server: 

    # yum module install postgresql:13/server

  2. Initialize the database cluster: 

    # postgresql-setup --initdb
* Initializing database in '/var/lib/pgsql/data'
* Initialized, logs are in /var/lib/pgsql/initdb_postgresql.log

  3. Set the password hashing algorithm to scram-sha-256.

    1. In the /var/lib/pgsql/data/postgresql.conf file, change the following line: 

      #password_encryption = md5              # md5 or scram-sha-256

      to: 

      password_encryption = scram-sha-256

    2. In the /var/lib/pgsql/data/pg_hba.conf file, change the following line for the IPv4 local connections: 

      host    all             all             127.0.0.1/32            ident

      to: 

      host    all             all             127.0.0.1/32            scram-sha-256

  4. Start the postgresql service: 

    # systemctl start postgresql.service

  5. Log in as the system user named postgres: 

    # su - postgres

  6. Start the PostgreSQL interactive terminal: 

    $ psql
psql (13.7)
Type "help" for help.

postgres=#

  7. Optional: Obtain information about the current database connection: 

    postgres=# \conninfo
You are connected to database "postgres" as user "postgres" via socket in "/var/run/postgresql" at port "5432".

  8. Create a user named mydbuser, set a password for mydbuser, and assign mydbuser the CREATEROLE and CREATEDB permissions: 

    postgres=# CREATE USER mydbuser WITH PASSWORD 'mypasswd' CREATEROLE CREATEDB;
CREATE ROLE

    The mydbuser user now can perform routine database management operations: create databases and manage user indexes.

  9. Log out of the interactive terminal by using the \q meta command: 

    postgres=# \q

  10. Log out of the postgres user session: 

    $ logout

  11. Log in to the PostgreSQL terminal as mydbuser, specify the hostname, and connect to the default postgres database, which was created during initialization: 

    # psql -U mydbuser -h 127.0.0.1 -d postgres
Password for user mydbuser:
Type the password.
psql (13.7)
Type "help" for help.

postgres=>

  12. Create a database named mydatabase: 

    postgres=> CREATE DATABASE mydatabase;
CREATE DATABASE
postgres=>

  13. Log out of the session: 

    postgres=# \q

  14. Connect to mydatabase as mydbuser: 

    # psql -U mydbuser -h 127.0.0.1 -d mydatabase
Password for user mydbuser:
psql (13.7)
Type "help" for help.
mydatabase=>

  15. Optional: Obtain information about the current database connection: 

    mydatabase=> \conninfo
You are connected to database "mydatabase" as user "mydbuser" on host "127.0.0.1" at port "5432".

9.4.4. Configuring PostgreSQL

In a PostgreSQL database, all data and configuration files are stored in a single directory called a database cluster. Red Hat recommends storing all data, including configuration files, in the default /var/lib/pgsql/data/ directory.

PostgreSQL configuration consists of the following files:

  • postgresql.conf - is used for setting the database cluster parameters.
  • postgresql.auto.conf - holds basic PostgreSQL settings similarly to postgresql.conf. However, this file is under the server control. It is edited by the ALTER SYSTEM queries, and cannot be edited manually.
  • pg_ident.conf - is used for mapping user identities from external authentication mechanisms into the PostgreSQL user identities.
  • pg_hba.conf - is used for configuring client authentication for PostgreSQL databases.

To change the PostgreSQL configuration, use the following procedure.

Procedure

  1. Edit the respective configuration file, for example, /var/lib/pgsql/data/postgresql.conf.

  2. Restart the postgresql service so that the changes become effective: 

    # systemctl restart postgresql.service

Example 9.2. Configuring PostgreSQL database cluster parameters

This example shows basic settings of the database cluster parameters in the /var/lib/pgsql/data/postgresql.conf file. 

# This is a comment
log_connections = yes
log_destination = 'syslog'
search_path = '"$user", public'
shared_buffers = 128MB
password_encryption = scram-sha-256

Example 9.3. Setting client authentication in PostgreSQL

This example demonstrates how to set client authentication in the /var/lib/pgsql/data/pg_hba.conf file. 

# TYPE    DATABASE       USER        ADDRESS              METHOD
local     all            all                              trust
host      postgres       all         192.168.93.0/24      ident
host      all            all         .example.com         scram-sha-256

9.4.5. Configuring TLS encryption on a PostgreSQL server

By default, PostgreSQL uses unencrypted connections. For more secure connections, you can enable Transport Layer Security (TLS) support on the PostgreSQL server and configure your clients to establish encrypted connections.

Prerequisites

  • The PostgreSQL server is installed.
  • The database cluster is initialized.

Procedure

  1. Install the OpenSSL library: 

    # yum install openssl

  2. Generate a TLS certificate and a key: 

    # openssl req -new -x509 -days 365 -nodes -text -out server.crt \
  -keyout server.key -subj "/CN=dbhost.yourdomain.com"

    Replace dbhost.yourdomain.com with your database host and domain name.

  3. Copy your signed certificate and your private key to the required locations on the database server: 

    # cp server.{key,crt} /var/lib/pgsql/data/.

  4. Change the owner and group ownership of the signed certificate and your private key to the postgres user: 

    # chown postgres:postgres /var/lib/pgsql/data/server.{key,crt}

  5. Restrict the permissions for your private key so that it is readable only by the owner: 

    # chmod 0400 /var/lib/pgsql/data/server.key

  6. Set the password hashing algorithm to scram-sha-256 by changing the following line in the /var/lib/pgsql/data/postgresql.conf file: 

    #password_encryption = md5              # md5 or scram-sha-256

    to: 

    password_encryption = scram-sha-256

  7. Configure PostgreSQL to use SSL/TLS by changing the following line in the /var/lib/pgsql/data/postgresql.conf file: 

    #ssl = off

    to: 

    ssl=on

  8. Restrict access to all databases to accept only connections from clients using TLS by changing the following line for the IPv4 local connections in the /var/lib/pgsql/data/pg_hba.conf file: 

    host		all		all		127.0.0.1/32		ident

    to: 

    hostssl 	all		all		127.0.0.1/32		scram-sha-256

    Alternatively, you can restrict access for a single database and a user by adding the following new line: 

    hostssl	mydatabase	mydbuser	127.0.0.1/32		scram-sha-256

    Replace mydatabase with the database name and mydbuser with the username.

  9. Make the changes effective by restarting the postgresql service: 

    # systemctl restart postgresql.service

Verification

  • To manually verify that the connection is encrypted:

    1. Connect to the PostgreSQL database as the mydbuser user, specify the host name and the database name: 

      $ psql -U mydbuser -h 127.0.0.1 -d mydatabase
Password for user mydbuser:

      Replace mydatabase with the database name and mydbuser with the username.

    2. Obtain information about the current database connection: 

      mydbuser=> \conninfo
You are connected to database "mydatabase" as user "mydbuser" on host "127.0.0.1" at port "5432".
SSL connection (protocol: TLSv1.3, cipher: TLS_AES_256_GCM_SHA384, bits: 256, compression: off)

  • You can write a simple application that verifies whether a connection to PostgreSQL is encrypted. This example demonstrates such an application written in C that uses the libpq client library, which is provided by the libpq-devel package: 

    #include <stdio.h>
#include <stdlib.h>
#include <libpq-fe.h>

int main(int argc, char* argv[])
{
//Create connection
PGconn* connection = PQconnectdb("hostaddr=127.0.0.1 password=mypassword port=5432 dbname=mydatabase user=mydbuser");

if (PQstatus(connection) ==CONNECTION_BAD)
    {
    printf("Connection error\n");
    PQfinish(connection);
    return -1; //Execution of the program will stop here
    }
    printf("Connection ok\n");
    //Verify TLS
    if (PQsslInUse(connection)){
     printf("TLS in use\n");
     printf("%s\n", PQsslAttribute(connection,"protocol"));
    }
    //End connection
    PQfinish(connection);
    printf("Disconnected\n");
    return 0;
}

    Replace mypassword with the password, mydatabase with the database name, and mydbuser with the username.

    Note

    You must load the pq libraries for compilation by using the -lpq option. For example, to compile the application by using the GCC compiler: 

    $ gcc source_file.c -lpq -o myapplication

    where the source_file.c contains the example code above, and myapplication is the name of your application for verifying secured PostgreSQL connection.

Example 9.4. Initializing, creating, and connecting to a PostgreSQL database using TLS encryption

This example demonstrates how to initialize a PostgreSQL database, create a database user and a database, and how to connect to the database using a secured connection.

  1. Install the PosgreSQL server: 

    # yum module install postgresql:13/server

  2. Initialize the database cluster: 

    # postgresql-setup --initdb
* Initializing database in '/var/lib/pgsql/data'
* Initialized, logs are in /var/lib/pgsql/initdb_postgresql.log

  3. Install the OpenSSL library: 

    # yum install openssl

  4. Generate a TLS certificate and a key: 

    # openssl req -new -x509 -days 365 -nodes -text -out server.crt \
  -keyout server.key -subj "/CN=dbhost.yourdomain.com"

    Replace dbhost.yourdomain.com with your database host and domain name.

  5. Copy your signed certificate and your private key to the required locations on the database server: 

    # cp server.{key,crt} /var/lib/pgsql/data/.

  6. Change the owner and group ownership of the signed certificate and your private key to the postgres user: 

    # chown postgres:postgres /var/lib/pgsql/data/server.{key,crt}

  7. Restrict the permissions for your private key so that it is readable only by the owner: 

    # chmod 0400 /var/lib/pgsql/data/server.key

  8. Set the password hashing algorithm to scram-sha-256. In the /var/lib/pgsql/data/postgresql.conf file, change the following line: 

    #password_encryption = md5              # md5 or scram-sha-256

    to: 

    password_encryption = scram-sha-256

  9. Configure PostgreSQL to use SSL/TLS. In the /var/lib/pgsql/data/postgresql.conf file, change the following line: 

    #ssl = off

    to: 

    ssl=on

  10. Start the postgresql service: 

    # systemctl start postgresql.service

  11. Log in as the system user named postgres: 

    # su - postgres

  12. Start the PostgreSQL interactive terminal as the postgres user: 

    $ psql -U postgres
psql (13.7)
Type "help" for help.

postgres=#

  13. Create a user named mydbuser and set a password for mydbuser: 

    postgres=# CREATE USER mydbuser WITH PASSWORD 'mypasswd';
CREATE ROLE
postgres=#

  14. Create a database named mydatabase: 

    postgres=# CREATE DATABASE mydatabase;
CREATE DATABASE
postgres=#

  15. Grant all permissions to the mydbuser user: 

    postgres=# GRANT ALL PRIVILEGES ON DATABASE mydatabase TO mydbuser;
GRANT
postgres=#

  16. Log out of the interactive terminal: 

    postgres=# \q

  17. Log out of the postgres user session: 

    $ logout

  18. Restrict access to all databases to accept only connections from clients using TLS by changing the following line for the IPv4 local connections in the /var/lib/pgsql/data/pg_hba.conf file: 

    host		all		all		127.0.0.1/32		ident

    to: 

    hostssl 	all		all		127.0.0.1/32		scram-sha-256

  19. Make the changes effective by restarting the postgresql service: 

    # systemctl restart postgresql.service

  20. Connect to the PostgreSQL database as the mydbuser user, specify the host name and the database name: 

    $ psql -U mydbuser -h 127.0.0.1 -d mydatabase
Password for user mydbuser:
psql (13.7)
SSL connection (protocol: TLSv1.3, cipher: TLS_AES_256_GCM_SHA384, bits: 256, compression: off)
Type "help" for help.

mydatabase=>

9.4.6. Backing up PostgreSQL data

To back up PostgreSQL data, use one of the following approaches:

SQL dump
See Backing up with SQL dump.
File system level backup
See File system level backup.
Continuous archiving
See Continuous archiving.

9.4.6.1. Backing up PostgreSQL data with an SQL dump

The SQL dump method is based on generating a dump file with SQL commands. When a dump is uploaded back to the database server, it recreates the database in the same state as it was at the time of the dump.

The SQL dump is ensured by the following PostgreSQL client applications:

  • pg_dump dumps a single database without cluster-wide information about roles or tablespaces
  • pg_dumpall dumps each database in a given cluster and preserves cluster-wide data, such as role and tablespace definitions.

By default, the pg_dump and pg_dumpall commands write their results into the standard output. To store the dump in a file, redirect the output to an SQL file. The resulting SQL file can be either in a text format or in other formats that allow for parallelism and for more detailed control of object restoration.

You can perform the SQL dump from any remote host that has access to the database.

9.4.6.1.1. Advantages and disadvantages of an SQL dump

An SQL dump has the following advantages compared to other PostgreSQL backup methods:

  • An SQL dump is the only PostgreSQL backup method that is not server version-specific. The output of the pg_dump utility can be reloaded into later versions of PostgreSQL, which is not possible for file system level backups or continuous archiving.
  • An SQL dump is the only method that works when transferring a database to a different machine architecture, such as going from a 32-bit to a 64-bit server.
  • An SQL dump provides internally consistent dumps. A dump represents a snapshot of the database at the time pg_dump began running.
  • The pg_dump utility does not block other operations on the database when it is running.

A disadvantage of an SQL dump is that it takes more time compared to file system level backup.

9.4.6.1.2. Performing an SQL dump using pg_dump

To dump a single database without cluster-wide information, use the pg_dump utility.

Prerequisites

  • You must have read access to all tables that you want to dump. To dump the entire database, you must run the commands as the postgres superuser or a user with database administrator privileges.

Procedure

  • Dump a database without cluster-wide information: 

    $ pg_dump dbname > dumpfile

To specify which database server pg_dump will contact, use the following command-line options:

  • The -h option to define the host.

    The default host is either the local host or what is specified by the PGHOST environment variable.

  • The -p option to define the port.

    The default port is indicated by the PGPORT environment variable or the compiled-in default.

9.4.6.1.3. Performing an SQL dump using pg_dumpall

To dump each database in a given database cluster and to preserve cluster-wide data, use the pg_dumpall utility.

Prerequisites

  • You must run the commands as the postgres superuser or a user with database administrator privileges.

Procedure

  • Dump all databases in the database cluster and preserve cluster-wide data:

    $ pg_dumpall > dumpfile

To specify which database server pg_dumpall will contact, use the following command-line options:

  • The -h option to define the host.

    The default host is either the local host or what is specified by the PGHOST environment variable.

  • The -p option to define the port.

    The default port is indicated by the PGPORT environment variable or the compiled-in default.

  • The -l option to define the default database.

    This option enables you to choose a default database different from the postgres database created automatically during initialization.

9.4.6.1.4. Restoring a database dumped using pg_dump

To restore a database from an SQL dump that you dumped using the pg_dump utility, follow the steps below.

Prerequisites

  • You must run the commands as the postgres superuser or a user with database administrator privileges.

Procedure

  1. Create a new database: 

    $ createdb dbname
  2. Verify that all users who own objects or were granted permissions on objects in the dumped database already exist. If such users do not exist, the restore fails to recreate the objects with the original ownership and permissions.

  3. Run the psql utility to restore a text file dump created by the pg_dump utility: 

    $ psql dbname < dumpfile

    where dumpfile is the output of the pg_dump command. To restore a non-text file dump, use the pg_restore utility instead: 

    $ pg_restore non-plain-text-file
9.4.6.1.5. Restoring databases dumped using pg_dumpall

To restore data from a database cluster that you dumped using the pg_dumpall utility, follow the steps below.

Prerequisites

  • You must run the commands as the postgres superuser or a user with database administrator privileges.

Procedure

  1. Ensure that all users who own objects or were granted permissions on objects in the dumped databases already exist. If such users do not exist, the restore fails to recreate the objects with the original ownership and permissions.

  2. Run the psql utility to restore a text file dump created by the pg_dumpall utility: 

    $ psql < dumpfile

    where dumpfile is the output of the pg_dumpall command.

9.4.6.1.6. Performing an SQL dump of a database on another server

Dumping a database directly from one server to another is possible because pg_dump and psql can write to and read from pipes.

Procedure

  • To dump a database from one server to another, run: 

    $ pg_dump -h host1 dbname | psql -h host2 dbname
9.4.6.1.7. Handling SQL errors during restore

By default, psql continues to execute if an SQL error occurs, causing the database to restore only partially.

To change the default behavior, use one of the following approaches when restoring a dump.

Prerequisites

  • You must run the commands as the postgres superuser or a user with database administrator privileges.

Procedure

  • Make psql exit with an exit status of 3 if an SQL error occurs by setting the ON_ERROR_STOP variable:

    $ psql --set ON_ERROR_STOP=on dbname < dumpfile

  • Specify that the whole dump is restored as a single transaction so that the restore is either fully completed or canceled.

    • When restoring a text file dump using the psql utility: 

      $ psql -1

    • When restoring a non-text file dump using the pg_restore utility: 

      $ pg_restore -e

      Note that when using this approach, even a minor error can cancel a restore operation that has already run for many hours.

9.4.6.1.8. Additional resources

9.4.6.2. Backing up PostgreSQL data with a file system level backup

To create a file system level backup, copy PostgreSQL database files to another location. For example, you can use any of the following approaches:

  • Create an archive file using the tar utility.
  • Copy the files to a different location using the rsync utility.
  • Create a consistent snapshot of the data directory.
9.4.6.2.1. Advantages and limitations of file system backing up

File system level backing up has the following advantage compared to other PostgreSQL backup methods:

  • File system level backing up is usually faster than an SQL dump.

File system level backing up has the following limitations compared to other PostgreSQL backup methods:

  • This backing up method is not suitable when you want to upgrade from RHEL 7 to RHEL 8 and migrate your data to the upgraded system. File system level backup is specific to an architecture and a RHEL major version. You can restore your data on your RHEL 7 system if the upgrade is not successful but you cannot restore the data on a RHEL 8 system.
  • The database server must be shut down before backing up and restoring data.
  • Backing up and restoring certain individual files or tables is impossible. Backing up a file system works only for complete backing up and restoring of an entire database cluster.
9.4.6.2.2. Performing file system level backing up

To perform file system level backing up, use the following procedure.

Procedure

  1. Choose the location of a database cluster and initialize this cluster: 

    # postgresql-setup --initdb

  2. Stop the postgresql service: 

    # systemctl stop postgresql.service

  3. Use any method to create a file system backup, for example a tar archive: 

    $ tar -cf backup.tar /var/lib/pgsql/data

  4. Start the postgresql service: 

    # systemctl start postgresql.service

Additional resources

9.4.6.3. Backing up PostgreSQL data by continuous archiving

9.4.6.3.1. Introduction to continuous archiving

PostgreSQL records every change made to the database’s data files into a write ahead log (WAL) file that is available in the pg_wal/ subdirectory of the cluster’s data directory. This log is intended primarily for a crash recovery. After a crash, the log entries made since the last checkpoint can be used for restoring the database to a consistency.

The continuous archiving method, also known as an online backup, combines the WAL files with a copy of the database cluster in the form of a base backup performed on a running server or a file system level backup.

If a database recovery is needed, you can restore the database from the copy of the database cluster and then replay log from the backed up WAL files to bring the system to the current state.

With the continuous archiving method, you must keep a continuous sequence of all archived WAL files that extends at minimum back to the start time of your last base backup. Therefore the ideal frequency of base backups depends on:

  • The storage volume available for archived WAL files.
  • The maximum possible duration of data recovery in situations when recovery is necessary. In cases with a long period since the last backup, the system replays more WAL segments, and the recovery therefore takes more time.
Note

You cannot use pg_dump and pg_dumpall SQL dumps as a part of a continuous archiving backup solution. SQL dumps produce logical backups and do not contain enough information to be used by a WAL replay.

To perform a database backup and restore using the continuous archiving method, follow these instructions:

  1. Set up and test your procedure for archiving WAL files - see WAL archiving.
  2. Perform a base backup - see base backup.

To restore your data, follow instructions in Restoring database with continuous archiving.

9.4.6.3.2. Advantages and disadvantages of continuous archiving

Continuous archiving has the following advantages compared to other PostgreSQL backup methods:

  • With the continuous backup method, it is possible to use a base backup that is not entirely consistent because any internal inconsistency in the backup is corrected by the log replay. Therefore you can perform a base backup on a running PostgreSQL server.
  • A file system snapshot is not needed; tar or a similar archiving utility is sufficient.
  • Continuous backup can be achieved by continuing to archive the WAL files because the sequence of WAL files for the log replay can be indefinitely long. This is particularly valuable for large databases.
  • Continuous backup supports point-in-time recovery. It is not necessary to replay the WAL entries to the end. The replay can be stopped at any point and the database can be restored to its state at any time since the base backup was taken.
  • If the series of WAL files are continuously available to another machine that has been loaded with the same base backup file, it is possible to restore the other machine with a nearly-current copy of the database at any point.

Continuous archiving has the following disadvantages compared to other PostgreSQL backup methods:

  • Continuous backup method supports only restoration of an entire database cluster, not a subset.
  • Continuous backup requires extensive archival storage.
9.4.6.3.3. Setting up WAL archiving

A running PostgreSQL server produces a sequence of write ahead log (WAL) records. The server physically divides this sequence into WAL segment files, which are given numeric names that reflect their position in the WAL sequence. Without WAL archiving, the segment files are reused and renamed to higher segment numbers.

When archiving WAL data, the contents of each segment file are captured and saved at a new location before the segment file is reused. You have multiple options where to save the content, such as an NFS-mounted directory on another machine, a tape drive, or a CD.

Note that WAL records do not include changes to configuration files.

To enable WAL archiving, use the following procedure.

Procedure

  1. In the /var/lib/pgsql/data/postgresql.conf file:

    1. Set the wal_level configuration parameter to replica or higher.
    2. Set the archive_mode parameter to on.
    3. Specify the shell command in the archive_command configuration parameter. You can use the cp command, another command, or a shell script.

  2. Restart the postgresql service to enable the changes: 

    # systemctl restart postgresql.service
  3. Test your archive command and ensure it does not overwrite an existing file and that it returns a non-zero exit status if it fails.
  4. To protect your data, ensure that the segment files are archived into a directory that does not have group or world read access.
Note

The archive command is executed only on completed WAL segments. A server that generates little WAL traffic can have a substantial delay between the completion of a transaction and its safe recording in archive storage. To limit how old unarchived data can be, you can:

  • Set the archive_timeout parameter to force the server to switch to a new WAL segment file with a given frequency.
  • Use the pg_switch_wal parameter to force a segment switch to ensure that a transaction is archived immediately after it finishes.

Example 9.5. Shell command for archiving WAL segments

This example shows a simple shell command you can set in the archive_command configuration parameter.

The following command copies a completed segment file to the required location: 

archive_command = 'test ! -f /mnt/server/archivedir/%f && cp %p /mnt/server/archivedir/%f'

where the %p parameter is replaced by the relative path to the file to archive and the %f parameter is replaced by the file name.

This command copies archivable WAL segments to the /mnt/server/archivedir/ directory. After replacing the %p and %f parameters, the executed command looks as follows: 

test ! -f /mnt/server/archivedir/00000001000000A900000065 && cp pg_wal/00000001000000A900000065 /mnt/server/archivedir/00000001000000A900000065

A similar command is generated for each new file that is archived.

Additional resources

9.4.6.3.4. Making a base backup

You can create a base backup in several ways. The simplest way of performing a base backup is using the pg_basebackup utility on a running PostgreSQL server.

The base backup process creates a backup history file that is stored into the WAL archive area and is named after the first WAL segment file that you need for the base backup.

The backup history file is a small text file containing the starting and ending times, and WAL segments of the backup. If you used the label string to identify the associated dump file, you can use the backup history file to determine which dump file to restore.

Note

Consider keeping several backup sets to be certain that you can recover your data.

To perform a base backup, use the following procedure.

Prerequisites

  • You must run the commands as the postgres superuser, a user with database administrator privileges, or another user with at least REPLICATION permissions.
  • You must keep all the WAL segment files generated during and after the base backup.

Procedure

  1. Use the pg_basebackup utility to perform the base backup.

    • To create a base backup as individual files (plain format): 

      $ pg_basebackup -D backup_directory -Fp

      Replace backup_directory with your desired backup location.

      If you use tablespaces and perform the base backup on the same host as the server, you must also use the --tablespace-mapping option, otherwise the backup will fail upon an attempt to write the backup to the same location.

    • To create a base backup as a tar archive (tar and compressed format): 

      $ pg_basebackup -D backup_directory -Ft -z

      Replace backup_directory with your desired backup location.

      To restore such data, you must manually extract the files in the correct locations.

  2. After the base backup process is complete, safely archive the copy of the database cluster and the WAL segment files used during the backup, which are specified in the backup history file.
  3. Delete WAL segments numerically lower than the WAL segment files used in the base backup because these are older than the base backup and no longer needed for a restore.

To specify which database server pg_basebackup will contact, use the following command-line options:

  • The -h option to define the host.

    The default host is either the local host or a host specified by the PGHOST environment variable.

  • The -p option to define the port.

    The default port is indicated by the PGPORT environment variable or the compiled-in default.

Additional resources

9.4.6.3.5. Restoring the database using a continuous archive backup

To restore a database using a continuous backup, use the following procedure.

Procedure

  1. Stop the server: 

    # systemctl stop postgresql.service

  2. Copy the necessary data to a temporary location.

    Preferably, copy the whole cluster data directory and any tablespaces. Note that this requires enough free space on your system to hold two copies of your existing database.

    If you do not have enough space, save the contents of the cluster’s pg_wal directory, which can contain logs that were not archived before the system went down.

  3. Remove all existing files and subdirectories under the cluster data directory and under the root directories of any tablespaces you are using.

  4. Restore the database files from your base backup.

    Ensure that:

    • The files are restored with the correct ownership (the database system user, not root).
    • The files are restored with the correct permissions.
    • The symbolic links in the pg_tblspc/ subdirectory are restored correctly.

  5. Remove any files present in the pg_wal/ subdirectory.

    These files resulted from the base backup and are therefore obsolete. If you did not archive pg_wal/, recreate it with proper permissions.

  6. Copy any unarchived WAL segment files that you saved in step 2 into pg_wal/.

  7. Create the recovery.conf recovery command file in the cluster data directory and specify the shell command in the restore_command configuration parameter. You can use the cp command, another command, or a shell script. For example: 

    restore_command = 'cp /mnt/server/archivedir/%f "%p"'

  8. Start the server: 

    # systemctl start postgresql.service

    The server will enter the recovery mode and proceed to read through the archived WAL files that it needs.

    If the recovery is terminated due to an external error, the server can be restarted and it will continue the recovery. When the recovery process is completed, the server renames recovery.conf to recovery.done. This prevents the server from accidental re-entering the recovery mode after it starts normal database operations.

  9. Check the contents of the database to verify that the database has recovered into the required state.

    If the database has not recovered into the required state, return to step 1. If the database has recovered into the required state, allow the users to connect by restoring the client authentication configuration in the pg_hba.conf file.

For more information about restoring using the continuous backup, see PostgreSQL Documentation.

9.4.6.3.6. Additional resources

9.4.7. Migrating to a RHEL 8 version of PostgreSQL

Red Hat Enterprise Linux 7 contains PostgreSQL 9.2 as the default version of the PostgreSQL server. In addition, several versions of PostgreSQL are provided as Software Collections for RHEL 7.

Red Hat Enterprise Linux 8 provides PostgreSQL 10 as the default postgresql stream, PostgreSQL 9.6, PostgreSQL 12, PostgreSQL 13, and PostgreSQL 15.

Users of PostgreSQL on Red Hat Enterprise Linux can use two migration paths for the database files:

The fast upgrade method is quicker than the dump and restore process. However, in certain cases, the fast upgrade does not work, and you can only use the dump and restore process. Such cases include:

  • Cross-architecture upgrades
  • Systems using the plpython or plpython2 extensions. Note that RHEL 8 AppStream repository includes only the postgresql-plpython3 package, not the postgresql-plpython2 package.
  • Fast upgrade is not supported for migration from Red Hat Software Collections versions of PostgreSQL.

As a prerequisite for migration to a later version of PostgreSQL, back up all your PostgreSQL databases.

Dumping the databases and performing backup of the SQL files is required for the dump and restore process and recommended for the fast upgrade method.

Before migrating to a later version of PostgreSQL, see the upstream compatibility notes for the version of PostgreSQL to which you want to migrate, as well as for all skipped PostgreSQL versions between the one you are migrating from and the target version.

9.4.7.1. Notable differences between PostgreSQL 13 and PostgreSQL 15

PostgreSQL 15 introduced the following backwards incompatible changes.

Default permissions of the public schema

The default permissions of the public schema have been modified in PostgreSQL 15. Newly created users need to grant permission explicitly by using the GRANT ALL ON SCHEMA public TO myuser; command.

The following example works in PostgreSQL 13 and earlier: 

postgres=# CREATE USER mydbuser;
postgres=# \c postgres mydbuser
postgres=$ CREATE TABLE mytable (id int);

The following example works in PostgreSQL 15: 

postgres=# CREATE USER mydbuser;
postgres=# GRANT ALL ON SCHEMA public TO mydbuser;
postgres=# \c postgres mydbuser
postgres=$ CREATE TABLE mytable (id int);
Note

Ensure that the mydbuser acces is configured appropriately in the pg_hba.conf file. See Creating PostgreSQL users for more information.

PQsendQuery() no longer supported in pipeline mode

Since PostgreSQL 15, the libpq PQsendQuery() function is no longer supported in pipeline mode. Modify affected applications to use the PQsendQueryParams() function instead.

9.4.7.2. Fast upgrade using the pg_upgrade utility

During a fast upgrade, you must copy binary data files to the /var/lib/pgsql/data/ directory and use the pg_upgrade utility.

You can use this method for migrating data:

  • From the RHEL 7 system version of PostgreSQL 9.2 to the RHEL 8 version of PostgreSQL 10
  • From the RHEL 8 version of PostgreSQL 10 to the RHEL 8 version of PostgreSQL 12
  • From the RHEL 8 version of PostgreSQL 12 to the RHEL 8 version of PostgreSQL 13
  • From the RHEL 8 version of PostgreSQL 13 to the RHEL 8 version of PostgreSQL 15

If you want to upgrade from an earlier postgresql stream within RHEL 8, follow the procedure described in Switching to a later stream and then migrate your PostgreSQL data.

For migrating between other combinations of PostgreSQL versions within RHEL, and for migration from the Red Hat Software Collections versions of PostgreSQL to RHEL, use Dump and restore upgrade.

The following procedure describes migration from the RHEL 7 system version of PostgreSQL 9.2 to a RHEL 8 version of PostgreSQL using the fast upgrade method.

Prerequisites

  • Before performing the upgrade, back up all your data stored in the PostgreSQL databases. By default, all data is stored in the /var/lib/pgsql/data/ directory on both the RHEL 7 and RHEL 8 systems.

Procedure

  1. On the RHEL 8 system, enable the stream (version) to which you want to migrate: 

    # yum module enable postgresql:stream

    Replace stream with the selected version of the PostgreSQL server.

    You can omit this step if you want to use the default stream, which provides PostgreSQL 10.

  2. On the RHEL 8 system, install the postgresql-server and postgresql-upgrade packages: 

    # yum install postgresql-server postgresql-upgrade

    Optionally, if you used any PostgreSQL server modules on RHEL 7, install them also on the RHEL 8 system in two versions, compiled both against PostgreSQL 9.2 (installed as the postgresql-upgrade package) and the target version of PostgreSQL (installed as the postgresql-server package). If you need to compile a third-party PostgreSQL server module, build it both against the postgresql-devel and postgresql-upgrade-devel packages.

  3. Check the following items:

    • Basic configuration: On the RHEL 8 system, check whether your server uses the default /var/lib/pgsql/data directory and the database is correctly initialized and enabled. In addition, the data files must be stored in the same path as mentioned in the /usr/lib/systemd/system/postgresql.service file.
    • PostgreSQL servers: Your system can run multiple PostgreSQL servers. Ensure that the data directories for all these servers are handled independently.
    • PostgreSQL server modules: Ensure that the PostgreSQL server modules that you used on RHEL 7 are installed on your RHEL 8 system as well. Note that plug-ins are installed in the /usr/lib64/pgsql/ directory (or in the /usr/lib/pgsql/ directory on 32-bit systems).

  4. Ensure that the postgresql service is not running on either of the source and target systems at the time of copying data. 

    # systemctl stop postgresql.service
  5. Copy the database files from the source location to the /var/lib/pgsql/data/ directory on the RHEL 8 system.

  6. Perform the upgrade process by running the following command as the PostgreSQL user: 

    # postgresql-setup --upgrade

    This launches the pg_upgrade process in the background.

    In case of failure, postgresql-setup provides an informative error message.

  7. Copy the prior configuration from /var/lib/pgsql/data-old to the new cluster.

    Note that the fast upgrade does not reuse the prior configuration in the newer data stack and the configuration is generated from scratch. If you want to combine the old and new configurations manually, use the *.conf files in the data directories.

  8. Start the new PostgreSQL server: 

    # systemctl start postgresql.service

  9. Analyze the new database cluster.

    • For PostgreSQL 13 or earlier: 

      su postgres -c '~/analyze_new_cluster.sh'

    • For PostgreSQL 15: 

      su postgres -c 'vacuumdb --all --analyze-in-stages'

  10. If you want the new PostgreSQL server to be automatically started on boot, run: 

    # systemctl enable postgresql.service

9.4.7.3. Dump and restore upgrade

When using the dump and restore upgrade, you must dump all databases contents into an SQL file dump file.

Note that the dump and restore upgrade is slower than the fast upgrade method and it might require some manual fixing in the generated SQL file.

You can use this method for migrating data from:

  • The Red Hat Enterprise Linux 7 system version of PostgreSQL 9.2
  • Any earlier Red Hat Enterprise Linux 8 version of PostgreSQL

  • An earlier or equal version of PostgreSQL from Red Hat Software Collections:

    • PostgreSQL 9.2 (no longer supported)
    • PostgreSQL 9.4 (no longer supported)
    • PostgreSQL 9.6 (no longer supported)
    • PostgreSQL 10
    • PostgreSQL 12
    • PostgreSQL 13

On RHEL 7 and RHEL 8 systems, PostgreSQL data is stored in the /var/lib/pgsql/data/ directory by default. In case of Red Hat Software Collections versions of PostgreSQL, the default data directory is /var/opt/rh/collection_name/lib/pgsql/data/ (with the exception of postgresql92, which uses the /opt/rh/postgresql92/root/var/lib/pgsql/data/ directory).

If you want to upgrade from an earlier postgresql stream within RHEL 8, follow the procedure described in Switching to a later stream and then migrate your PostgreSQL data.

To perform the dump and restore upgrade, change the user to root.

The following procedure describes migration from the RHEL 7 system version of PostgreSQL 9.2 to a RHEL 8 version of PostgreSQL.

Procedure

  1. On your RHEL 7 system, start the PostgreSQL 9.2 server: 

    # systemctl start postgresql.service

  2. On the RHEL 7 system, dump all databases contents into the pgdump_file.sql file: 

    su - postgres -c "pg_dumpall > ~/pgdump_file.sql"

  3. Verify that the databases were dumped correctly: 

    su - postgres -c 'less "$HOME/pgdump_file.sql"'

    As a result, the path to the dumped sql file is displayed: /var/lib/pgsql/pgdump_file.sql.

  4. On the RHEL 8 system, enable the stream (version) to which you wish to migrate: 

    # yum module enable postgresql:stream

    Replace stream with the selected version of the PostgreSQL server.

    You can omit this step if you want to use the default stream, which provides PostgreSQL 10.

  5. On the RHEL 8 system, install the postgresql-server package: 

    # yum install postgresql-server

    Optionally, if you used any PostgreSQL server modules on RHEL 7, install them also on the RHEL 8 system. If you need to compile a third-party PostgreSQL server module, build it against the postgresql-devel package.

  6. On the RHEL 8 system, initialize the data directory for the new PostgreSQL server: 

    # postgresql-setup --initdb

  7. On the RHEL 8 system, copy the pgdump_file.sql into the PostgreSQL home directory, and check that the file was copied correctly: 

    su - postgres -c 'test -e "$HOME/pgdump_file.sql" && echo exists'

  8. Copy the configuration files from the RHEL 7 system: 

    su - postgres -c 'ls -1 $PGDATA/*.conf'

    The configuration files to be copied are:

    • /var/lib/pgsql/data/pg_hba.conf
    • /var/lib/pgsql/data/pg_ident.conf
    • /var/lib/pgsql/data/postgresql.conf

  9. On the RHEL 8 system, start the new PostgreSQL server: 

    # systemctl start postgresql.service

  10. On the RHEL 8 system, import data from the dumped sql file: 

    su - postgres -c 'psql -f ~/pgdump_file.sql postgres'
Note

When upgrading from a Red Hat Software Collections version of PostgreSQL, adjust the commands to include scl enable collection_name. For example, to dump data from the rh-postgresql96 Software Collection, use the following command: 

su - postgres -c 'scl enable rh-postgresql96 "pg_dumpall > ~/pgdump_file.sql"'

Chapter 10. Deploying and configuring a Postfix SMTP server

As a system administrator, you can configure your email infrastructure by using a mail transport agent (MTA), such as Postfix, to transport email messages between hosts using the SMTP protocol. Postfix is a server-side application for routing and delivering mail. You can use Postfix to set up a local mail server, create a null-client mail relay, use a Postfix server as a destination for multiple domains, or choose an LDAP directory instead of files for lookups.

The key features of Postfix:

  • Security features to protect against common email related threats
  • Customization options, including support for virtual domains and aliases

10.1. Overview of the main Postfix configuration files

The postfix package provides multiple configuration files in the /etc/postfix/ directory.

To configure your email infrastructure, use the following configuration files:

  • main.cf — contains the global configuration of Postfix.
  • master.cf — specifies Postfix interaction with various processes to accomplish mail delivery.
  • access — specifies access rules, for example hosts that are allowed to connect to Postfix.
  • transport — maps email addresses to relay hosts.
  • aliases — contains a configurable list required by the mail protocol that describes user ID aliases. Note that you can find this file in the /etc/ directory.

10.2. Installing and configuring a Postfix SMTP server

You can configure your Postfix SMTP server to receive, store, and deliver email messages. If the mail server package is not selected during the system installation, Postfix will not be available by default. Perform the following steps to install Postfix:

Prerequisites

Procedure

  1. Install Postfix: 

    # yum install postfix

  2. To configure Postfix, edit the /etc/postfix/main.cf file and make the following changes:

    1. By default, Postfix receives emails only on the loopback interface. To configure Postfix to listen on specific interfaces, update the inet_interfaces parameter to the IP addresses of these interfaces: 

      inet_interfaces = 127.0.0.1/32, [::1]/128, 192.0.2.1, [2001:db8:1::1]

      To configure Postfix to listen on all interfaces, set: 

      inet_interfaces = all

    2. If you want that Postfix uses a different hostname than the fully-qualified domain name (FQDN) that is returned by the gethostname() function, add the myhostname parameter: 

      myhostname = <smtp.example.com>

      For example, Postfix adds this hostname to header of emails it processes.

    3. If the domain name differs from the one in the myhostname parameter, add the mydomain parameter: 

      mydomain = <example.com>

    4. Add the myorigin parameter and set it to the value of mydomain: 

      myorigin = $mydomain

      With this setting, Postfix uses the domain name as origin for locally posted mails instead of the hostname.

    5. Add the mynetworks parameter, and define the IP ranges of trusted networks that are allowed to send mails: 

      mynetworks = 127.0.0.1/32, [::1]/128, 192.0.2.1/24, [2001:db8:1::1]/64

      If clients from not trustworthy networks, such as the Internet, should be able to send mails through this server, you must configure relay restrictions in a later step.

  3. Verify if the Postfix configuration in the main.cf file is correct: 

    $ postfix check

  4. Enable the postfix service to start at boot and start it: 

    # systemctl enable --now postfix

  5. Allow the smtp traffic through firewall and reload the firewall rules: 

    # firewall-cmd --permanent --add-service smtp

# firewall-cmd --reload

Verification

  1. Verify that the postfix service is running: 

    # systemctl status postfix

    • Optional: Restart the postfix service, if the output is stopped, waiting, or the service is not running: 

      # systemctl restart postfix

    • Optional: Reload the postfix service after changing any options in the configuration files in the /etc/postfix/ directory to apply those changes: 

      # systemctl reload postfix

  2. Verify the email communication between local users on your system: 

    # echo "This is a test message" | mail -s <SUBJECT> <user@mydomain.com>

  3. Verify that your mail server is not an open relay by sending an email to an email address outside of your domain from a client (server1) to your mail server (server2):

    1. Edit the /etc/postfix/main.cf file for server1 as follows: 

      relayhost = <ip_address_of_server2>

    2. Edit the /etc/postfix/main.cf file for server2 as follows: 

      mynetworks = <ip_address_of_server2>

    3. On server1, send the following mail: 

      # echo "This is an open relay test message" | mail -s <SUBJECT> <user@example.com>

    4. Check the /var/log/maillog file: 

      554 Relay access denied - the server is not going to relay.
250 OK or similar - the server is going to relay.

Troubleshooting

  • In case of errors, check the /var/log/maillog file.

Additional resources

10.3. Customizing TLS settings of a Postfix server

To make your email traffic encrypted and therefore more secure, you can configure Postfix to use a certificate from a trusted certificate authority (CA) instead of the self-signed certificate and customize the Transport Layer Security (TLS) security settings. In RHEL 8, the TLS encryption protocol is enabled in the Postfix server by default. The basic Postfix TLS configuration contains self-signed certificates for inbound SMTP and the opportunistic TLS for outbound SMTP.

Prerequisites

  • You have the root access.
  • You have the postfix package installed on your server.
  • You have a certificate signed by a trusted certificate authority (CA) and a private key.

  • You have copied the following files to the Postfix server:

    • The server certificate: /etc/pki/tls/certs/postfix.pem
    • The private key: /etc/pki/tls/private/postfix.key

Procedure

  1. Set the path to the certificate and private key files on the server where Postfix is running by adding the following lines to the /etc/postfix/main.cf file: 

    smtpd_tls_cert_file = /etc/pki/tls/certs/postfix.pem
smtpd_tls_key_file = /etc/pki/tls/private/postfix.key

  2. Restrict the incoming SMTP connections to authenticated users only by editing the /etc/postfix/main.cf file: 

    smtpd_tls_auth_only = yes

  3. Reload the postfix service to apply the changes: 

    # systemctl reload postfix

Verification

  • Configure your client to use TLS encryption and send an email.

    Note

    To get additional information about Postfix client TLS activity, increase the log level from 0 to 1 by changing the following line in the /etc/postfix/main.cf: 

    smtp_tls_loglevel = 1

10.4. Configuring Postfix to forward all emails to a mail relay

If you want to forward all email to a mail relay, you can configure Postfix server as a null client. In this configuration Postfix only forwards mail to a different mail server and is not capable of receiving mail.

Prerequisites

  • You have the root access.
  • You have the postfix package installed on your server.
  • You have the IP address or hostname of the relay host to which you want to forward emails.

Procedure

  1. To prevent Postfix from accepting any local email delivery and making it a null client, edit the /etc/postfix/main.cf file and make the following changes:

    1. Configure Postfix to forward all email by setting the mydestination parameter equal to an empty value: 

      mydestination =

      In this configuration the Postfix server is not a destination for any email and acts as a null client.

    2. Specify the mail relay server that receives the email from your null client: 

      relayhost = <[ip_address_or_hostname]>

      The relay host is responsible for the mail delivery. Enclose <ip_address_or_hostname> in square brackets.

    3. Configure the Postfix mail server to listen only on the loopback interface for emails to deliver: 

      inet_interfaces = loopback-only

    4. If you want Postfix to rewrite the sender domain of all outgoing emails to the company domain of your relay mail server, set: 

      myorigin = <relay.example.com>

    5. To disable the local mail delivery, add the following directive at the end of the configuration file: 

      local_transport = error: local delivery disabled

    6. Add the mynetworks parameter so that Postfix forwards email from the local system originating from the 127.0.0.0/8 IPv4 network and the [::1]/128 IPv6 network to the mail relay server: 

      mynetworks = 127.0.0.0/8, [::1]/128

  2. Verify if the Postfix configuration in the main.cf file is correct: 

    $ postfix check

  3. Restart the postfix service to apply the changes: 

    # systemctl restart postfix

Verification

  • Verify that the email communication is forwarded to the mail relay: 

    # echo "This is a test message" | mail -s <SUBJECT> <user@example.com>

Troubleshooting

  • In case of errors, check the /var/log/maillog file.

Additional resources

  • The /etc/postfix/main.cf configuration file

10.5. Configuring Postfix as a destination for multiple domains

You can configure Postfix as a mail server that can receive emails for multiple domains. In this configuration, Postfix acts as the final destination for emails sent to addresses within the specified domains. You can configure the following:

  • Set up multiple email addresses that point to the same email destination
  • Route incoming email for multiple domains to the same Postfix server

Prerequisites

  • You have the root access.
  • You have configured a Postfix server.

Procedure

  1. In the /etc/postfix/virtual virtual alias file, specify the email addresses for each domain. Add each email address on a new line: 

    <info@example.com>  <user22@example.net>
<sales@example.com>  <user11@example.org>

    In this example, Postfix redirects all emails sent to info@example.com to user22@example.net and email sent to sales@example.com to user11@example.org.

  2. Create a hash file for the virtual alias map: 

    # postmap /etc/postfix/virtual

    This command creates the /etc/postfix/virtual.db file. Note that you must always re-run this command after you update the /etc/postfix/virtual file.

  3. In the Postfix /etc/postfix/main.cf configuration file, add the virtual_alias_maps parameter and point it to the hash file: 

    virtual_alias_maps = hash:/etc/postfix/virtual

  4. Reload the postfix service to apply the changes: 

    # systemctl reload postfix

Verification

  • Test the configuration by sending an email to one of the virtual email addresses.

Troubleshooting

  • In case of errors, check the /var/log/maillog file.

10.6. Using an LDAP directory as a lookup table

If you use a Lightweight Directory Access Protocol (LDAP) server to store accounts, domains or aliases, you can configure Postfix to use the LDAP server as a lookup table. Using LDAP instead of files for lookups enables you to have a central database.

Prerequisites

  • You have the root access.
  • You have the postfix package installed on your server.
  • You have an LDAP server with the required schema and user credentials.
  • You have the postfix-ldap plugin installed on the server running Postfix.

Procedure

  1. Configure the LDAP lookup parameters by creating a /etc/postfix/ldap-aliases.cf file with the following content:

    1. Specify the hostname of the LDAP server: 

      server_host = <ldap.example.com>

    2. Specify the base domain name for the LDAP search: 

      search_base = dc=<example>,dc=<com>
    3. Optional: Customize the LDAP search filter and attributes based on your requirements. The filter for searching the directory defaults to query_filter = mailacceptinggeneralid=%s.

  2. Enable the LDAP source as a lookup table in the /etc/postfix/main.cf configuration file by adding the following content: 

    virtual_alias_maps = ldap:/etc/postfix/ldap-aliases.cf

  3. Verify the LDAP configuration by running the postmap command, which checks for any syntax errors or connectivity issues: 

    # postmap -q @<example.com> ldap:/etc/postfix/ldap-aliases.cf

  4. Reload the postfix service to apply the changes: 

    # systemctl reload postfix

Verification

  • Send a test email to verify that the LDAP lookup works correctly. Check the mail logs in /var/log/maillog for any errors.

Additional resources

  • /usr/share/doc/postfix/README_FILES/LDAP_README file
  • /usr/share/doc/postfix/README_FILES/DATABASE_README file

10.7. Configuring Postfix as an outgoing mail server to relay for authenticated users

You can configure Postfix to relay mail for authenticated users. In this scenario, you allow users to authenticate themselves and use their email address to send mail through your SMTP server by configuring Postfix as an outgoing mail server with SMTP authentication, TLS encryption, and sender address restrictions.

Prerequisites

  • You have the root access.
  • You have configured a Postfix server.

Procedure

  1. To configure Postfix as an outgoing mail server, edit the /etc/postfix/main.cf file and add the following:

    1. Enable SMTP authentication: 

      smtpd_sasl_auth_enable = yes
broken_sasl_auth_clients = yes

    2. Disable access without TLS: 

      smtpd_tls_auth_only = yes

    3. Allow mail relaying only for authenticated users: 

      smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated defer_unauth_destination

    4. Optional: Restrict users to use their own email address only as a sender: 

      smtpd_sender_restrictions = reject_sender_login_mismatch

  2. Reload the postfix service to apply the changes: 

    # systemctl reload postfix

Verification

  • Authenticate in your SMTP client that supports TLS and SASL. Send an test email to verify that the SMTP authentication works correctly.

10.8. Delivering email from Postfix to Dovecot running on the same host

You can configure Postfix to deliver incoming mail to Dovecot on the same host using LMTP over a UNIX socket. This socket enables direct communication between Postfix and Dovecot on the local machine.

Prerequisites

Procedure

  1. Configure Postfix to use the LMTP protocol and the UNIX domain socket for delivering mail to Dovecot in the /etc/postfix/main.cf file:

    • If you want to use virtual mailboxes, add the following content: 

      virtual_transport = lmtp:unix:/var/run/dovecot/lmtp

    • If you want to use non-virtual mailboxes, add the following content: 

      mailbox_transport = lmtp:unix:/var/run/dovecot/lmtp

  2. Reload postfix to apply the changes: 

    # systemctl reload postfix

Verification

  • Send an test email to verify that the LMTP socket works correctly. Check the mail logs in /var/log/maillog for any errors.

10.9. Delivering email from Postfix to Dovecot running on a different host

You can establish a secure connection between Postfix mail server and the Dovecot delivery agent over the network. To do so, configure the LMTP service to use network socket for delivering mail between mail servers. By default, the LMTP protocol is not encrypted. However, if you configured TLS encryption, Dovecot uses the same settings automatically for the LMTP service. SMTP servers can then connect to it using the STARTTLS command over LMTP.

Prerequisites

Procedure

  1. Configure Postfix to use the LMTP protocol and the INET domain socket for delivering mail to Dovecot in the /etc/postfix/main.cf file by adding the following content: 

    mailbox_transport = lmtp:inet:<dovecot_host>:<port>

    Replace <dovecot_host> with the IP address or hostname of the Dovecot server and <port> with the port number of the LMTP service.

  2. Reload the postfix service to apply the changes: 

    # systemctl reload postfix

Verification

  • Send an test email to an address hosted by the remote Dovecot server and check the Dovecot logs to ensure that the mail was successfully delivered.

10.10. Securing the Postfix service

Postfix is a mail transfer agent (MTA) that uses the Simple Mail Transfer Protocol (SMTP) to deliver electronic messages between other MTAs and to email clients or delivery agents. Although MTAs can encrypt traffic between one another, they might not do so by default. You can also mitigate risks to various attacks by changing setting to more secure values.

10.10.2. Postfix configuration options for limiting DoS attacks

An attacker can flood the server with traffic, or send information that triggers a crash, causing a denial of service (DoS) attack. You can configure your system to reduce the risk of such attacks by setting limits in the /etc/postfix/main.cf file. You can change the value of the existing directives or you can add new directives with custom values in the <directive> = <value> format.

Use the following list of directives for limiting a DoS attack:

smtpd_client_connection_rate_limit
This directive limits the maximum number of connection attempts any client can make to this service per time unit. The default value is 0, which means a client can make as many connections per time unit as Postfix can accept. By default, the directive excludes clients in trusted networks.
anvil_rate_time_unit
This directive is a time unit to calculate the rate limit. The default value is 60 seconds.
smtpd_client_event_limit_exceptions
This directive excludes clients from the connection and rate limit commands. By default, the directive excludes clients in trusted networks.
smtpd_client_message_rate_limit
This directive defines the maximum number of message deliveries from client to request per time unit (regardless of whether or not Postfix actually accepts those messages).
default_process_limit
This directive defines the default maximum number of Postfix child processes that provide a given service. You can ignore this rule for specific services in the master.cf file. By default, the value is 100.
queue_minfree
This directive defines the minimum amount of free space required to receive mail in the queue file system. The directive is currently used by the Postfix SMTP server to decide if it accepts any mail at all. By default, the Postfix SMTP server rejects MAIL FROM commands when the amount of free space is less than 1.5 times the message_size_limit. To specify a higher minimum free space limit, specify a queue_minfree value that is at least 1.5 times the message_size_limit. By default, the queue_minfree value is 0.
header_size_limit
This directive defines the maximum amount of memory in bytes for storing a message header. If a header is large, it discards the excess header. By default, the value is 102400 bytes.
message_size_limit
This directive defines the maximum size of a message including the envelope information in bytes. By default, the value is 10240000 bytes.

10.10.3. Configuring Postfix to use SASL

Postfix supports Simple Authentication and Security Layer (SASL) based SMTP Authentication (AUTH). SMTP AUTH is an extension of the Simple Mail Transfer Protocol. Currently, the Postfix SMTP server supports the SASL implementations in the following ways:

Dovecot SASL
The Postfix SMTP server can communicate with the Dovecot SASL implementation using either a UNIX-domain socket or a TCP socket. Use this method if Postfix and Dovecot applications are running on separate machines.
Cyrus SASL
When enabled, SMTP clients must authenticate with the SMTP server using an authentication method supported and accepted by both the server and the client.

Prerequisites

  • The dovecot package is installed on the system

Procedure

  1. Set up Dovecot:

    1. Include the following lines in the /etc/dovecot/conf.d/10-master.conf file: 

      service auth {
  unix_listener /var/spool/postfix/private/auth {
    mode = 0660
    user = postfix
    group = postfix
  }
}

      The previous example uses UNIX-domain sockets for communication between Postfix and Dovecot. The example also assumes default Postfix SMTP server settings, which include the mail queue located in the /var/spool/postfix/ directory, and the application running under the postfix user and group.

    2. Optional: Set up Dovecot to listen for Postfix authentication requests through TCP: 

      service auth {
  inet_listener {
      port = port-number
  }
}

    3. Specify the method that the email client uses to authenticate with Dovecot by editing the auth_mechanisms parameter in /etc/dovecot/conf.d/10-auth.conf file: 

      auth_mechanisms = plain login

      The auth_mechanisms parameter supports different plaintext and non-plaintext authentication methods.

  2. Set up Postfix by modifying the /etc/postfix/main.cf file:

    1. Enable SMTP Authentication on the Postfix SMTP server: 

      smtpd_sasl_auth_enable = yes

    2. Enable the use of Dovecot SASL implementation for SMTP Authentication: 

      smtpd_sasl_type = dovecot

    3. Provide the authentication path relative to the Postfix queue directory. Note that the use of a relative path ensures that the configuration works regardless of whether the Postfix server runs in chroot or not: 

      smtpd_sasl_path = private/auth

      This step uses UNIX-domain sockets for communication between Postfix and Dovecot.

      To configure Postfix to look for Dovecot on a different machine in case you use TCP sockets for communication, use configuration values similar to the following: 

      smtpd_sasl_path = inet: ip-address : port-number

      In the previous example, replace the ip-address with the IP address of the Dovecot machine and port-number with the port number specified in Dovecot’s /etc/dovecot/conf.d/10-master.conf file.

    4. Specify SASL mechanisms that the Postfix SMTP server makes available to clients. Note that you can specify different mechanisms for encrypted and unencrypted sessions. 

      smtpd_sasl_security_options = noanonymous, noplaintext
smtpd_sasl_tls_security_options = noanonymous

      The previous directives specify that during unencrypted sessions, no anonymous authentication is allowed and no mechanisms that transmit unencrypted user names or passwords are allowed. For encrypted sessions that use TLS, only non-anonymous authentication mechanisms are allowed.

Additional resources

Chapter 11. Configuring and maintaining a Dovecot IMAP and POP3 server

Dovecot is a high-performance mail delivery agent (MDA) with a focus on security. You can use IMAP or POP3-compatible email clients to connect to a Dovecot server and read or download emails.

Key features of Dovecot:

  • The design and implementation focuses on security
  • Two-way replication support for high availability to improve the performance in large environments
  • Supports the high-performance dbox mailbox format, but also mbox and Maildir for compatibility reasons
  • Self-healing features, such as fixing broken index files
  • Compliance with the IMAP standards
  • Workaround support to bypass bugs in IMAP and POP3 clients

11.1. Setting up a Dovecot server with PAM authentication

Dovecot supports the Name Service Switch (NSS) interface as a user database and the Pluggable Authentication Modules (PAM) framework as an authentication backend. With this configuration, Dovecot can provide services to users who are available locally on the server through NSS.

Use PAM authentication if accounts:

  • Are defined locally in the /etc/passwd file
  • Are stored in a remote database but they are available locally through the System Security Services Daemon (SSSD) or other NSS plugins.

11.1.1. Installing Dovecot

The dovecot package provides:

  • The dovecot service and the utilities to maintain it
  • Services that Dovecot starts on demand, such as for authentication
  • Plugins, such as server-side mail filtering
  • Configuration files in the /etc/dovecot/ directory
  • Documentation in the /usr/share/doc/dovecot/ directory

Procedure

  • Install the dovecot package: 

    # yum install dovecot
    Note

    If Dovecot is already installed and you require clean configuration files, rename or remove the /etc/dovecot/ directory. Afterwards, reinstall the package. Without removing the configuration files, the yum reinstall dovecot command does not reset the configuration files in /etc/dovecot/.

Next step

11.1.2. Configuring TLS encryption on a Dovecot server

Dovecot provides a secure default configuration. For example, TLS is enabled by default to transmit credentials and data encrypted over networks. To configure TLS on a Dovecot server, you only need to set the paths to the certificate and private key files. Additionally, you can increase the security of TLS connections by generating and using Diffie-Hellman parameters to provide perfect forward secrecy (PFS).

Prerequisites

  • Dovecot is installed.

  • The following files have been copied to the listed locations on the server:

    • The server certificate: /etc/pki/dovecot/certs/server.example.com.crt
    • The private key: /etc/pki/dovecot/private/server.example.com.key
    • The Certificate Authority (CA) certificate: /etc/pki/dovecot/certs/ca.crt
  • The hostname in the Subject DN field of the server certificate matches the server’s Fully-qualified Domain Name (FQDN).

Procedure

  1. Set secure permissions on the private key file: 

    # chown root:root /etc/pki/dovecot/private/server.example.com.key
# chmod 600 /etc/pki/dovecot/private/server.example.com.key

  2. Generate a file with Diffie-Hellman parameters: 

    # openssl dhparam -out /etc/dovecot/dh.pem 4096

    Depending on the hardware and entropy on the server, generating Diffie-Hellman parameters with 4096 bits can take several minutes.

  3. Set the paths to the certificate and private key files in the /etc/dovecot/conf.d/10-ssl.conf file:

    1. Update the ssl_cert and ssl_key parameters, and set them to use the paths of the server’s certificate and private key: 

      ssl_cert = </etc/pki/dovecot/certs/server.example.com.crt
ssl_key = </etc/pki/dovecot/private/server.example.com.key

    2. Uncomment the ssl_ca parameter, and set it to use the path to the CA certificate: 

      ssl_ca = </etc/pki/dovecot/certs/ca.crt

    3. Uncomment the ssl_dh parameter, and set it to use the path to the Diffie-Hellman parameters file: 

      ssl_dh = </etc/dovecot/dh.pem
    Important

    To ensure that Dovecot reads the value of a parameter from a file, the path must start with a leading < character.

Next step

Additional resources

  • /usr/share/doc/dovecot/wiki/SSL.DovecotConfiguration.txt

11.1.3. Preparing Dovecot to use virtual users

By default, Dovecot performs many actions on the file system as the user who uses the service. However, configuring the Dovecot back end to use one local user to perform these actions has several benefits:

  • Dovecot performs file system actions as a specific local user instead of using the user’s ID (UID).
  • Users do not need to be available locally on the server.
  • You can store all mailboxes and user-specific files in one root directory.
  • Users do not require a UID and group ID (GID), which reduces administration efforts.
  • Users who have access to the file system on the server cannot compromise their mailboxes or indexes because they cannot access these files.
  • Setting up replication is easier.

Prerequisites

  • Dovecot is installed.

Procedure

  1. Create the vmail user: 

    # useradd --home-dir /var/mail/ --shell /usr/sbin/nologin vmail

    Dovecot will later use this user to manage the mailboxes. For security reasons, do not use the dovecot or dovenull system users for this purpose.

  2. If you use a different path than /var/mail/, set the mail_spool_t SELinux context on it, for example: 

    # semanage fcontext -a -t mail_spool_t "<path>(/.*)?"
# restorecon -Rv <path>

  3. Grant write permissions on /var/mail/ only to the vmail user: 

    # chown vmail:vmail /var/mail/
# chmod 700 /var/mail/

  4. Uncomment the mail_location parameter in the /etc/dovecot/conf.d/10-mail.conf file, and set it to the mailbox format and location: 

    mail_location = sdbox:/var/mail/%n/

    With this setting:

    • Dovecot uses the high-performant dbox mailbox format in single mode. In this mode, the service stores each mail in a separate file, similar to the maildir format.
    • Dovecot resolves the %n variable in the path to the username. This is required to ensure that each user has a separate directory for its mailbox.

Next step

Additional resources

  • /usr/share/doc/dovecot/wiki/VirtualUsers.txt
  • /usr/share/doc/dovecot/wiki/MailLocation.txt
  • /usr/share/doc/dovecot/wiki/MailboxFormat.dbox.txt
  • /usr/share/doc/dovecot/wiki/Variables.txt

11.1.4. Using PAM as the Dovecot authentication backend

By default, Dovecot uses the Name Service Switch (NSS) interface as the user database and the Pluggable Authentication Modules (PAM) framework as the authentication backend.

Customize the settings to adapt Dovecot to your environment and to simplify administration by using the virtual users feature.

Prerequisites

  • Dovecot is installed.
  • The virtual users feature is configured.

Procedure

  1. Update the first_valid_uid parameter in the /etc/dovecot/conf.d/10-mail.conf file to define the lowest user ID (UID) that can authenticate to Dovecot: 

    first_valid_uid = 1000

    By default, users with a UID greater than or equal to 1000 can authenticate. If required, you can also set the last_valid_uid parameter to define the highest UID that Dovecot allows to log in.

  2. In the /etc/dovecot/conf.d/auth-system.conf.ext file, add the override_fields parameter to the userdb section as follows: 

    userdb {
  driver = passwd
  override_fields = uid=vmail gid=vmail home=/var/mail/%n/
}

    Due to the fixed values, Dovecot does not query these settings from the /etc/passwd file. As a result, the home directory defined in /etc/passwd does not need to exist.

Next step

Additional resources

  • /usr/share/doc/dovecot/wiki/PasswordDatabase.PAM.txt
  • /usr/share/doc/dovecot/wiki/VirtualUsers.Home.txt

11.1.5. Completing the Dovecot configuration

Once you have installed and configured Dovecot, open the required ports in the firewalld service, and enable and start the service. Afterwards, you can test the server.

Prerequisites

  • The following has been configured in Dovecot:

    • TLS encryption
    • An authentication backend
  • Clients trust the Certificate Authority (CA) certificate.

Procedure

  1. If you want to provide only an IMAP or POP3 service to users, uncomment the protocols parameter in the /etc/dovecot/dovecot.conf file, and set it to the required protocols. For example, if you do not require POP3, set: 

    protocols = imap lmtp

    By default, the imap, pop3, and lmtp protocols are enabled.

  2. Open the ports in the local firewall. For example, to open the ports for the IMAPS, IMAP, POP3S, and POP3 protocols, enter: 

    # firewall-cmd --permanent --add-service=imaps --add-service=imap --add-service=pop3s --add-service=pop3
# firewall-cmd --reload

  3. Enable and start the dovecot service: 

    # systemctl enable --now dovecot

Verification

  1. Use a mail client, such as Mozilla Thunderbird, to connect to Dovecot and read emails. The settings for the mail client depend on the protocol you want to use:

    Table 11.1. Connection settings to the Dovecot server

    ProtocolPortConnection securityAuthentication method

    IMAP

    143

    STARTTLS

    PLAIN[a]

    IMAPS

    993

    SSL/TLS

    PLAIN[a]

    POP3

    110

    STARTTLS

    PLAIN[a]

    POP3S

    995

    SSL/TLS

    PLAIN[a]

    [a] The client transmits data encrypted through the TLS connection. Consequently, credentials are not disclosed.

    Note that this table does not list settings for unencrypted connections because, by default, Dovecot does not accept plain text authentication on connections without TLS.

  2. Display configuration settings with non-default values: 

    # doveconf -n

Additional resources

  • firewall-cmd(1) man page

11.2. Setting up a Dovecot server with LDAP authentication

If your infrastructure uses an LDAP server to store accounts, you can authenticate Dovecot users against it. In this case, you manage accounts centrally in the directory and, users do not required local access to the file system on the Dovecot server.

Centrally-managed accounts are also a benefit if you plan to set up multiple Dovecot servers with replication to make your mailboxes high available.

11.2.1. Installing Dovecot

The dovecot package provides:

  • The dovecot service and the utilities to maintain it
  • Services that Dovecot starts on demand, such as for authentication
  • Plugins, such as server-side mail filtering
  • Configuration files in the /etc/dovecot/ directory
  • Documentation in the /usr/share/doc/dovecot/ directory

Procedure

  • Install the dovecot package: 

    # yum install dovecot
    Note

    If Dovecot is already installed and you require clean configuration files, rename or remove the /etc/dovecot/ directory. Afterwards, reinstall the package. Without removing the configuration files, the yum reinstall dovecot command does not reset the configuration files in /etc/dovecot/.

Next step

11.2.2. Configuring TLS encryption on a Dovecot server

Dovecot provides a secure default configuration. For example, TLS is enabled by default to transmit credentials and data encrypted over networks. To configure TLS on a Dovecot server, you only need to set the paths to the certificate and private key files. Additionally, you can increase the security of TLS connections by generating and using Diffie-Hellman parameters to provide perfect forward secrecy (PFS).

Prerequisites

  • Dovecot is installed.

  • The following files have been copied to the listed locations on the server:

    • The server certificate: /etc/pki/dovecot/certs/server.example.com.crt
    • The private key: /etc/pki/dovecot/private/server.example.com.key
    • The Certificate Authority (CA) certificate: /etc/pki/dovecot/certs/ca.crt
  • The hostname in the Subject DN field of the server certificate matches the server’s Fully-qualified Domain Name (FQDN).

Procedure

  1. Set secure permissions on the private key file: 

    # chown root:root /etc/pki/dovecot/private/server.example.com.key
# chmod 600 /etc/pki/dovecot/private/server.example.com.key

  2. Generate a file with Diffie-Hellman parameters: 

    # openssl dhparam -out /etc/dovecot/dh.pem 4096

    Depending on the hardware and entropy on the server, generating Diffie-Hellman parameters with 4096 bits can take several minutes.

  3. Set the paths to the certificate and private key files in the /etc/dovecot/conf.d/10-ssl.conf file:

    1. Update the ssl_cert and ssl_key parameters, and set them to use the paths of the server’s certificate and private key: 

      ssl_cert = </etc/pki/dovecot/certs/server.example.com.crt
ssl_key = </etc/pki/dovecot/private/server.example.com.key

    2. Uncomment the ssl_ca parameter, and set it to use the path to the CA certificate: 

      ssl_ca = </etc/pki/dovecot/certs/ca.crt

    3. Uncomment the ssl_dh parameter, and set it to use the path to the Diffie-Hellman parameters file: 

      ssl_dh = </etc/dovecot/dh.pem
    Important

    To ensure that Dovecot reads the value of a parameter from a file, the path must start with a leading < character.

Next step

Additional resources

  • /usr/share/doc/dovecot/wiki/SSL.DovecotConfiguration.txt

11.2.3. Preparing Dovecot to use virtual users

By default, Dovecot performs many actions on the file system as the user who uses the service. However, configuring the Dovecot back end to use one local user to perform these actions has several benefits:

  • Dovecot performs file system actions as a specific local user instead of using the user’s ID (UID).
  • Users do not need to be available locally on the server.
  • You can store all mailboxes and user-specific files in one root directory.
  • Users do not require a UID and group ID (GID), which reduces administration efforts.
  • Users who have access to the file system on the server cannot compromise their mailboxes or indexes because they cannot access these files.
  • Setting up replication is easier.

Prerequisites

  • Dovecot is installed.

Procedure

  1. Create the vmail user: 

    # useradd --home-dir /var/mail/ --shell /usr/sbin/nologin vmail

    Dovecot will later use this user to manage the mailboxes. For security reasons, do not use the dovecot or dovenull system users for this purpose.

  2. If you use a different path than /var/mail/, set the mail_spool_t SELinux context on it, for example: 

    # semanage fcontext -a -t mail_spool_t "<path>(/.*)?"
# restorecon -Rv <path>

  3. Grant write permissions on /var/mail/ only to the vmail user: 

    # chown vmail:vmail /var/mail/
# chmod 700 /var/mail/

  4. Uncomment the mail_location parameter in the /etc/dovecot/conf.d/10-mail.conf file, and set it to the mailbox format and location: 

    mail_location = sdbox:/var/mail/%n/

    With this setting:

    • Dovecot uses the high-performant dbox mailbox format in single mode. In this mode, the service stores each mail in a separate file, similar to the maildir format.
    • Dovecot resolves the %n variable in the path to the username. This is required to ensure that each user has a separate directory for its mailbox.

Next step

Additional resources

  • /usr/share/doc/dovecot/wiki/VirtualUsers.txt
  • /usr/share/doc/dovecot/wiki/MailLocation.txt
  • /usr/share/doc/dovecot/wiki/MailboxFormat.dbox.txt
  • /usr/share/doc/dovecot/wiki/Variables.txt

11.2.4. Using LDAP as the Dovecot authentication backend

Users in an LDAP directory can usually authenticate themselves to the directory service. Dovecot can use this to authenticate users when they log in to the IMAP and POP3 services. This authentication method has a number of benefits, such as:

  • Administrators can manage users centrally in the directory.
  • The LDAP accounts do not require any special attributes. They only need to be able to authenticate to the LDAP server. Consequently, this method is independent from the password storage scheme used on the LDAP server.
  • Users do not need to be available locally on the server through the Name Service Switch (NSS) interface and the Pluggable Authentication Modules (PAM) framework.

Prerequisites

  • Dovecot is installed.
  • The virtual users feature is configured.
  • Connections to the LDAP server support TLS encryption.
  • RHEL on the Dovecot server trusts the Certificate Authority (CA) certificate of the LDAP server.
  • If users are stored in different trees in the LDAP directory, a dedicated LDAP account for Dovecot exists to search the directory. This account requires permissions to search for Distinguished Names (DNs) of other users.

Procedure

  1. Configure the authentication backends in the /etc/dovecot/conf.d/10-auth.conf file:

    1. Comment out include statements for auth-*.conf.ext authentication backend configuration files that you do not require, for example: 

      #!include auth-system.conf.ext

    2. Enable LDAP authentication by uncommenting the following line: 

      !include auth-ldap.conf.ext

  2. Edit the /etc/dovecot/conf.d/auth-ldap.conf.ext file, and add the override_fields parameter as follows to the userdb section: 

    userdb {
  driver = ldap
  args = /etc/dovecot/dovecot-ldap.conf.ext
  override_fields = uid=vmail gid=vmail home=/var/mail/%n/
}

    Due to the fixed values, Dovecot does not query these settings from the LDAP server. Consequently, these attributes also do not have to be present.

  3. Create the /etc/dovecot/dovecot-ldap.conf.ext file with the following settings:

    1. Depending on the LDAP structure, configure one of the following:

      • If users are stored in different trees in the LDAP directory, configure dynamic DN lookups: 

        dn = cn=dovecot_LDAP,dc=example,dc=com
dnpass = password
pass_filter = (&(objectClass=posixAccount)(uid=%n))

        Dovecot uses the specified DN, password, and filter to search the DN of the authenticating user in the directory. In this search, Dovecot replaces %n in the filter with the username. Note that the LDAP search must return only one result.

      • If all users are stored under a specific entry, configure a DN template: 

        auth_bind_userdn = cn=%n,ou=People,dc=example,dc=com

    2. Enable authentication binds to the LDAP server to verify Dovecot users: 

      auth_bind = yes

    3. Set the URL to the LDAP server: 

      uris = ldaps://LDAP-srv.example.com

      For security reasons, only use encrypted connections using LDAPS or the STARTTLS command over the LDAP protocol. For the latter, additionally add tls = yes to the settings.

      For a working certificate validation, the hostname of the LDAP server must match the hostname used in its TLS certificate.

    4. Enable the verification of the LDAP server’s TLS certificate: 

      tls_require_cert = hard

    5. Set the base DN to the DN where to start searching for users: 

      base = ou=People,dc=example,dc=com

    6. Set the search scope: 

      scope = onelevel

      Dovecot searches with the onelevel scope only in the specified base DN and with the subtree scope also in subtrees.

  4. Set secure permissions on the /etc/dovecot/dovecot-ldap.conf.ext file: 

    # chown root:root /etc/dovecot/dovecot-ldap.conf.ext
# chmod 600 /etc/dovecot/dovecot-ldap.conf.ext

Next step

Additional resources

  • /usr/share/doc/dovecot/example-config/dovecot-ldap.conf.ext
  • /usr/share/doc/dovecot/wiki/UserDatabase.Static.txt
  • /usr/share/doc/dovecot/wiki/AuthDatabase.LDAP.txt
  • /usr/share/doc/dovecot/wiki/AuthDatabase.LDAP.AuthBinds.txt
  • /usr/share/doc/dovecot/wiki/AuthDatabase.LDAP.PasswordLookups.txt

11.2.5. Completing the Dovecot configuration

Once you have installed and configured Dovecot, open the required ports in the firewalld service, and enable and start the service. Afterwards, you can test the server.

Prerequisites

  • The following has been configured in Dovecot:

    • TLS encryption
    • An authentication backend
  • Clients trust the Certificate Authority (CA) certificate.

Procedure

  1. If you want to provide only an IMAP or POP3 service to users, uncomment the protocols parameter in the /etc/dovecot/dovecot.conf file, and set it to the required protocols. For example, if you do not require POP3, set: 

    protocols = imap lmtp

    By default, the imap, pop3, and lmtp protocols are enabled.

  2. Open the ports in the local firewall. For example, to open the ports for the IMAPS, IMAP, POP3S, and POP3 protocols, enter: 

    # firewall-cmd --permanent --add-service=imaps --add-service=imap --add-service=pop3s --add-service=pop3
# firewall-cmd --reload

  3. Enable and start the dovecot service: 

    # systemctl enable --now dovecot

Verification

  1. Use a mail client, such as Mozilla Thunderbird, to connect to Dovecot and read emails. The settings for the mail client depend on the protocol you want to use:

    Table 11.2. Connection settings to the Dovecot server

    ProtocolPortConnection securityAuthentication method

    IMAP

    143

    STARTTLS

    PLAIN[a]

    IMAPS

    993

    SSL/TLS

    PLAIN[a]

    POP3

    110

    STARTTLS

    PLAIN[a]

    POP3S

    995

    SSL/TLS

    PLAIN[a]

    [a] The client transmits data encrypted through the TLS connection. Consequently, credentials are not disclosed.

    Note that this table does not list settings for unencrypted connections because, by default, Dovecot does not accept plain text authentication on connections without TLS.

  2. Display configuration settings with non-default values: 

    # doveconf -n

Additional resources

  • firewall-cmd(1) man page

11.3. Setting up a Dovecot server with MariaDB SQL authentication

If you store users and passwords in a MariaDB SQL server, you can configure Dovecot to use it as the user database and authentication backend. With this configuration, you manage accounts centrally in a database, and users have no local access to the file system on the Dovecot server.

Centrally managed accounts are also a benefit if you plan to set up multiple Dovecot servers with replication to make your mailboxes highly available.

11.3.1. Installing Dovecot

The dovecot package provides:

  • The dovecot service and the utilities to maintain it
  • Services that Dovecot starts on demand, such as for authentication
  • Plugins, such as server-side mail filtering
  • Configuration files in the /etc/dovecot/ directory
  • Documentation in the /usr/share/doc/dovecot/ directory

Procedure

  • Install the dovecot package: 

    # yum install dovecot
    Note

    If Dovecot is already installed and you require clean configuration files, rename or remove the /etc/dovecot/ directory. Afterwards, reinstall the package. Without removing the configuration files, the yum reinstall dovecot command does not reset the configuration files in /etc/dovecot/.

Next step

11.3.2. Configuring TLS encryption on a Dovecot server

Dovecot provides a secure default configuration. For example, TLS is enabled by default to transmit credentials and data encrypted over networks. To configure TLS on a Dovecot server, you only need to set the paths to the certificate and private key files. Additionally, you can increase the security of TLS connections by generating and using Diffie-Hellman parameters to provide perfect forward secrecy (PFS).

Prerequisites

  • Dovecot is installed.

  • The following files have been copied to the listed locations on the server:

    • The server certificate: /etc/pki/dovecot/certs/server.example.com.crt
    • The private key: /etc/pki/dovecot/private/server.example.com.key
    • The Certificate Authority (CA) certificate: /etc/pki/dovecot/certs/ca.crt
  • The hostname in the Subject DN field of the server certificate matches the server’s Fully-qualified Domain Name (FQDN).

Procedure

  1. Set secure permissions on the private key file: 

    # chown root:root /etc/pki/dovecot/private/server.example.com.key
# chmod 600 /etc/pki/dovecot/private/server.example.com.key

  2. Generate a file with Diffie-Hellman parameters: 

    # openssl dhparam -out /etc/dovecot/dh.pem 4096

    Depending on the hardware and entropy on the server, generating Diffie-Hellman parameters with 4096 bits can take several minutes.

  3. Set the paths to the certificate and private key files in the /etc/dovecot/conf.d/10-ssl.conf file:

    1. Update the ssl_cert and ssl_key parameters, and set them to use the paths of the server’s certificate and private key: 

      ssl_cert = </etc/pki/dovecot/certs/server.example.com.crt
ssl_key = </etc/pki/dovecot/private/server.example.com.key

    2. Uncomment the ssl_ca parameter, and set it to use the path to the CA certificate: 

      ssl_ca = </etc/pki/dovecot/certs/ca.crt

    3. Uncomment the ssl_dh parameter, and set it to use the path to the Diffie-Hellman parameters file: 

      ssl_dh = </etc/dovecot/dh.pem
    Important

    To ensure that Dovecot reads the value of a parameter from a file, the path must start with a leading < character.

Next step

Additional resources

  • /usr/share/doc/dovecot/wiki/SSL.DovecotConfiguration.txt

11.3.3. Preparing Dovecot to use virtual users

By default, Dovecot performs many actions on the file system as the user who uses the service. However, configuring the Dovecot back end to use one local user to perform these actions has several benefits:

  • Dovecot performs file system actions as a specific local user instead of using the user’s ID (UID).
  • Users do not need to be available locally on the server.
  • You can store all mailboxes and user-specific files in one root directory.
  • Users do not require a UID and group ID (GID), which reduces administration efforts.
  • Users who have access to the file system on the server cannot compromise their mailboxes or indexes because they cannot access these files.
  • Setting up replication is easier.

Prerequisites

  • Dovecot is installed.

Procedure

  1. Create the vmail user: 

    # useradd --home-dir /var/mail/ --shell /usr/sbin/nologin vmail

    Dovecot will later use this user to manage the mailboxes. For security reasons, do not use the dovecot or dovenull system users for this purpose.

  2. If you use a different path than /var/mail/, set the mail_spool_t SELinux context on it, for example: 

    # semanage fcontext -a -t mail_spool_t "<path>(/.*)?"
# restorecon -Rv <path>

  3. Grant write permissions on /var/mail/ only to the vmail user: 

    # chown vmail:vmail /var/mail/
# chmod 700 /var/mail/

  4. Uncomment the mail_location parameter in the /etc/dovecot/conf.d/10-mail.conf file, and set it to the mailbox format and location: 

    mail_location = sdbox:/var/mail/%n/

    With this setting:

    • Dovecot uses the high-performant dbox mailbox format in single mode. In this mode, the service stores each mail in a separate file, similar to the maildir format.
    • Dovecot resolves the %n variable in the path to the username. This is required to ensure that each user has a separate directory for its mailbox.

Next step

Additional resources

  • /usr/share/doc/dovecot/wiki/VirtualUsers.txt
  • /usr/share/doc/dovecot/wiki/MailLocation.txt
  • /usr/share/doc/dovecot/wiki/MailboxFormat.dbox.txt
  • /usr/share/doc/dovecot/wiki/Variables.txt

11.3.4. Using a MariaDB SQL database as the Dovecot authentication backend

Dovecot can read accounts and passwords from a MariaDB database and use it to authenticate users when they log in to the IMAP or POP3 service. The benefits of this authentication method include:

  • Administrators can manage users centrally in a database.
  • Users have no access locally on the server.

Prerequisites

  • Dovecot is installed.
  • The virtual users feature is configured.
  • Connections to the MariaDB server support TLS encryption.
  • The dovecotDB database exists in MariaDB, and the users table contains at least a username and password column.
  • The password column contains passwords encrypted with a scheme that Dovecot supports.
  • The passwords either use the same scheme or have a {pw-storage-scheme} prefix.
  • The dovecot MariaDB user has read permission on the users table in the dovecotDB database.
  • The certificate of the Certificate Authority (CA) that issued the MariaDB server’s TLS certificate is stored on the Dovecot server in the /etc/pki/tls/certs/ca.crt file.

Procedure

  1. Install the dovecot-mysql package: 

    # yum install dovecot-mysql

  2. Configure the authentication backends in the /etc/dovecot/conf.d/10-auth.conf file:

    1. Comment out include statements for auth-*.conf.ext authentication backend configuration files that you do not require, for example: 

      #!include auth-system.conf.ext

    2. Enable SQL authentication by uncommenting the following line: 

      !include auth-sql.conf.ext

  3. Edit the /etc/dovecot/conf.d/auth-sql.conf.ext file, and add the override_fields parameter to the userdb section as follows: 

    userdb {
  driver = sql
  args = /etc/dovecot/dovecot-sql.conf.ext
  override_fields = uid=vmail gid=vmail home=/var/mail/%n/
}

    Due to the fixed values, Dovecot does not query these settings from the SQL server.

  4. Create the /etc/dovecot/dovecot-sql.conf.ext file with the following settings: 

    driver = mysql
connect = host=mariadb_srv.example.com dbname=dovecotDB user=dovecot password=dovecotPW ssl_ca=/etc/pki/tls/certs/ca.crt
default_pass_scheme = SHA512-CRYPT
user_query = SELECT username FROM users WHERE username='%u';
password_query = SELECT username AS user, password FROM users WHERE username='%u';
iterate_query = SELECT username FROM users;

    To use TLS encryption to the database server, set the ssl_ca option to the path of the certificate of the CA that issued the MariaDB server certificate. For a working certificate validation, the hostname of the MariaDB server must match the hostname used in its TLS certificate.

    If the password values in the database contain a {pw-storage-scheme} prefix, you can omit the default_pass_scheme setting.

    The queries in the file must be set as follows:

    • For the user_query parameter, the query must return the username of the Dovecot user. The query must also return only one result.
    • For the password_query parameter, the query must return the username and the password, and Dovecot must use these values in the user and password variables. Therefore, if the database uses different column names, use the AS SQL command to rename a column in the result.
    • For the iterate_query parameter, the query must return a list of all users.

  5. Set secure permissions on the /etc/dovecot/dovecot-sql.conf.ext file: 

    # chown root:root /etc/dovecot/dovecot-sql.conf.ext
# chmod 600 /etc/dovecot/dovecot-sql.conf.ext

Next step

Additional resources

  • /usr/share/doc/dovecot/example-config/dovecot-sql.conf.ext
  • /usr/share/doc/dovecot/wiki/Authentication.PasswordSchemes.txt

11.3.5. Completing the Dovecot configuration

Once you have installed and configured Dovecot, open the required ports in the firewalld service, and enable and start the service. Afterwards, you can test the server.

Prerequisites

  • The following has been configured in Dovecot:

    • TLS encryption
    • An authentication backend
  • Clients trust the Certificate Authority (CA) certificate.

Procedure

  1. If you want to provide only an IMAP or POP3 service to users, uncomment the protocols parameter in the /etc/dovecot/dovecot.conf file, and set it to the required protocols. For example, if you do not require POP3, set: 

    protocols = imap lmtp

    By default, the imap, pop3, and lmtp protocols are enabled.

  2. Open the ports in the local firewall. For example, to open the ports for the IMAPS, IMAP, POP3S, and POP3 protocols, enter: 

    # firewall-cmd --permanent --add-service=imaps --add-service=imap --add-service=pop3s --add-service=pop3
# firewall-cmd --reload

  3. Enable and start the dovecot service: 

    # systemctl enable --now dovecot

Verification

  1. Use a mail client, such as Mozilla Thunderbird, to connect to Dovecot and read emails. The settings for the mail client depend on the protocol you want to use:

    Table 11.3. Connection settings to the Dovecot server

    ProtocolPortConnection securityAuthentication method

    IMAP

    143

    STARTTLS

    PLAIN[a]

    IMAPS

    993

    SSL/TLS

    PLAIN[a]

    POP3

    110

    STARTTLS

    PLAIN[a]

    POP3S

    995

    SSL/TLS

    PLAIN[a]

    [a] The client transmits data encrypted through the TLS connection. Consequently, credentials are not disclosed.

    Note that this table does not list settings for unencrypted connections because, by default, Dovecot does not accept plain text authentication on connections without TLS.

  2. Display configuration settings with non-default values: 

    # doveconf -n

Additional resources

  • firewall-cmd(1) man page

11.4. Configuring replication between two Dovecot servers

With two-way replication, you can make your Dovecot server high-available, and IMAP and POP3 clients can access a mailbox on both servers. Dovecot keeps track of changes in the index logs of each mailbox and solves conflicts in a safe way.

Perform this procedure on both replication partners.

Note

Replication works only between server pairs. Consequently, in a large cluster, you need multiple independent backend pairs.

Prerequisites

  • Both servers use the same authentication backend. Preferably, use LDAP or SQL to maintain accounts centrally.
  • The Dovecot user database configuration supports user listing. Use the doveadm user '*' command to verify this.
  • Dovecot accesses mailboxes on the file system as the vmail user instead of the user’s ID (UID).

Procedure

  1. Create the /etc/dovecot/conf.d/10-replication.conf file and perform the following steps in it:

    1. Enable the notify and replication plug-ins: 

      mail_plugins = $mail_plugins notify replication

    2. Add a service replicator section: 

      service replicator {
  process_min_avail = 1

  unix_listener replicator-doveadm {
    mode = 0600
    user = vmail
  }
}

      With these settings, Dovecot starts at least one replicator process when the dovecot service starts. Additionally, this section defines the settings on the replicator-doveadm socket.

    3. Add a service aggregator section to configure the replication-notify-fifo pipe and replication-notify socket: 

      service aggregator {
  fifo_listener replication-notify-fifo {
    user = vmail
  }
  unix_listener replication-notify {
    user = vmail
  }
}

    4. Add a service doveadm section to define the port of the replication service: 

      service doveadm {
  inet_listener {
    port = 12345
  }
}

    5. Set the password of the doveadm replication service: 

      doveadm_password = replication_password

      The password must be the same on both servers.

    6. Configure the replication partner: 

      plugin {
  mail_replica = tcp:server2.example.com:12345
}

    7. Optional: Define the maximum number of parallel dsync processes: 

      replication_max_conns = 20

      The default value of replication_max_conns is 10.

  2. Set secure permissions on the /etc/dovecot/conf.d/10-replication.conf file: 

    # chown root:root /etc/dovecot/conf.d/10-replication.conf
# chmod 600 /etc/dovecot/conf.d/10-replication.conf

  3. Enable the nis_enabled SELinux Boolean to allow Dovecot to open the doveadm replication port: 

    setsebool -P nis_enabled on

  4. Configure firewalld rules to allow only the replication partner to access the replication port, for example: 

    # firewall-cmd --permanent --zone=public --add-rich-rule="rule family="ipv4" source address="192.0.2.1/32" port protocol="tcp" port="12345" accept"
# firewall-cmd --permanent --zone=public --add-rich-rule="rule family="ipv6" source address="2001:db8:2::1/128" port protocol="tcp" port="12345" accept"
# firewall-cmd --reload

    The subnet masks /32 for the IPv4 and /128 for the IPv6 address limit the access to the specified addresses.

  5. Perform this procedure also on the other replication partner.

  6. Reload Dovecot: 

    # systemctl reload dovecot

Verification

  1. Perform an action in a mailbox on one server and then verify if Dovecot has replicated the change to the other server.

  2. Display the replicator status: 

    # doveadm replicator status
Queued 'sync' requests        0
Queued 'high' requests        0
Queued 'low' requests         0
Queued 'failed' requests      0
Queued 'full resync' requests 30
Waiting 'failed' requests     0
Total number of known users   75

  3. Display the replicator status of a specific user: 

    # doveadm replicator status example_user
username        priority  fast sync  full sync  success sync  failed
example_user    none      02:05:28   04:19:07   02:05:28      -

Additional resources

  • dsync(1) man page
  • /usr/share/doc/dovecot/wiki/Replication.txt

11.5. Automatically subscribing users to IMAP mailboxes

Typically, IMAP server administrators want Dovecot to automatically create certain mailboxes, such as Sent and Trash, and subscribe the users to them. You can set this in the configuration files.

Additionally, you can define special-use mailboxes. IMAP clients often support defining mailboxes for special purposes, such as for sent emails. To avoid that the user has to manually select and set the correct mailboxes, IMAP servers can send a special-use attribute in the IMAP LIST command. Clients can then use this attribute to identify and set, for example, the mailbox for sent emails.

Prerequisites

  • Dovecot is configured.

Procedure

  1. Update the inbox namespace section in the /etc/dovecot/conf.d/15-mailboxes.conf file:

    1. Add the auto = subscribe setting to each special-use mailbox that should be available to users, for example: 

      namespace inbox {
  ...
  mailbox Drafts {
    special_use = \Drafts
    auto = subscribe
  }

  mailbox Junk {
    special_use = \Junk
    auto = subscribe
  }

  mailbox Trash {
    special_use = \Trash
    auto = subscribe
  }

  mailbox Sent {
    special_use = \Sent
    auto = subscribe
  }
  ...
}

      If your mail clients support more special-use mailboxes, you can add similar entries. The special_use parameter defines the value that Dovecot sends in the special-use attribute to the clients.

    2. Optional: If you want to define other mailboxes that have no special purpose, add mailbox sections for them in the user’s inbox, for example: 

      namespace inbox {
  ...
  mailbox "Important Emails" {
    auto = <value>
  }
  ...
}

      You can set the auto parameter to one of the following values:

      • subscribe: Automatically creates the mailbox and subscribes the user to it.
      • create: Automatically creates the mailbox without subscribing the user to it.
      • no (default): Dovecot neither creates the mailbox nor does it subscribe the user to it.

  2. Reload Dovecot: 

    # systemctl reload dovecot

Verification

  • Use an IMAP client and access your mailbox.

    Mailboxes with the setting auto = subscribe are automatically visible. If the client supports special-use mailboxes and the defined purposes, the client automatically uses them.

Additional resources

11.6. Configuring an LMTP socket and LMTPS listener

SMTP servers, such as Postfix, use the Local Mail Transfer Protocol (LMTP) to deliver emails to Dovecot. If the SMTP server runs:

  • On the same host as Dovecot, use an LMTP socket

  • On a different host, use an LMTP service

    By default, the LMTP protocol is not encrypted. However, if you configured TLS encryption, Dovecot uses the same settings automatically for the LMTP service. SMTP servers can then connect to it using the LMTPS protocol or the STARTTLS command over LMTP.

Prerequisites

  • Dovecot is installed.
  • If you want to configure an LMTP service, TLS encryption is configured in Dovecot.

Procedure

  1. Verify that the LMTP protocol is enabled: 

    # doveconf -a | egrep "^protocols"
protocols = imap pop3 lmtp

    The protocol is enabled, if the output contains lmtp.

  2. If the lmtp protocol is disabled, edit the /etc/dovecot/dovecot.conf file, and append lmtp to the values in the protocols parameter: 

    protocols = ... lmtp

  3. Depending on whether you need an LMTP socket or service, make the following changes in the service lmtp section in the /etc/dovecot/conf.d/10-master.conf file:

    • LMTP socket: By default, Dovecot automatically creates the /var/run/dovecot/lmtp socket.

      Optional: Customize the ownership and permissions: 

      service lmtp {
  ...
  unix_listener lmtp {
    mode = 0600
    user = postfix
    group = postfix
  }
  ...
}

    • LMTP service: Add a inet_listener sub-section: 

      service lmtp {
  ...
  inet_listener lmtp {
    port = 24
  }
  ...
}

  4. Configure firewalld rules to allow only the SMTP server to access the LMTP port, for example: 

    # firewall-cmd --permanent --zone=public --add-rich-rule="rule family="ipv4" source address="192.0.2.1/32" port protocol="tcp" port="24" accept"
# firewall-cmd --permanent --zone=public --add-rich-rule="rule family="ipv6" source address="2001:db8:2::1/128" port protocol="tcp" port="24" accept"
# firewall-cmd --reload

    The subnet masks /32 for the IPv4 and /128 for the IPv6 address limit the access to the specified addresses.

  5. Reload Dovecot: 

    # systemctl reload dovecot

Verification

  1. If you configured the LMTP socket, verify that Dovecot has created the socket and that the permissions are correct: 

    # ls -l /var/run/dovecot/lmtp
srw-------. 1 postfix postfix 0 Nov 22 17:17 /var/run/dovecot/lmtp

  2. Configure the SMTP server to submit emails to Dovecot using the LMTP socket or service.

    When you use the LMTP service, ensure that the SMTP server uses the LMTPS protocol or sends the STARTTLS command to use an encrypted connection.

Additional resources

  • /usr/share/doc/dovecot/wiki/LMTP.txt

11.7. Disabling the IMAP or POP3 service in Dovecot

By default, Dovecot provides IMAP and POP3 services. If you require only one of them, you can disable the other to reduce the surface for attack.

Prerequisites

  • Dovecot is installed.

Procedure

  1. Uncomment the protocols parameter in the /etc/dovecot/dovecot.conf file, and set it to use the required protocols. For example, if you do not require POP3, set: 

    protocols = imap lmtp

    By default, the imap, pop3, and lmtp protocols are enabled.

  2. Reload Dovecot: 

    # systemctl reload dovecot

  3. Close the ports that are no longer required in the local firewall. For example, to close the ports for the POP3S and POP3 protocols, enter: 

    # firewall-cmd --remove-service=pop3s --remove-service=pop3
# firewall-cmd --reload

Verification

  • Display all ports in LISTEN mode opened by the dovecot process: 

    # ss -tulp | grep dovecot
tcp  LISTEN 0  100  0.0.0.0:993  0.0.0.0:*  users:(("dovecot",pid=1405,fd=44))
tcp  LISTEN 0  100  0.0.0.0:143  0.0.0.0:*  users:(("dovecot",pid=1405,fd=42))
tcp  LISTEN 0  100     [::]:993     [::]:*  users:(("dovecot",pid=1405,fd=45))
tcp  LISTEN 0  100     [::]:143     [::]:*  users:(("dovecot",pid=1405,fd=43))

    In this example, Dovecot listens only on the TCP ports 993 (IMAPS) and 143 (IMAP).

    Note that Dovecot only opens a port for the LMTP protocol if you configure the service to listen on a port instead of using a socket.

Additional resources

  • firewall-cmd(1) man page

11.8. Enabling server-side email filtering using Sieve on a Dovecot IMAP server

You can upload Sieve scripts to a server using the ManageSieve protocol. Sieve scripts define rules and actions that a server should validate and perform on incoming emails. For example, users can use Sieve to forward emails from a specific sender, and administrators can create a global filter to move mails flagged by a spam filter into a separate IMAP folder.

The ManageSieve plugin adds support for Sieve scripts and the ManageSieve protocol to a Dovecot IMAP server.

Warning

Use only clients that support using the ManageSieve protocol over TLS connections. Disabling TLS for this protocol causes clients to send credentials in plain text over the network.

Prerequisites

  • Dovecot is configured and provides IMAP mailboxes.
  • TLS encryption is configured in Dovecot.
  • The mail clients support the ManageSieve protocol over TLS connections.

Procedure

  1. Install the dovecot-pigeonhole package: 

    # yum install dovecot-pigeonhole

  2. Uncomment the following line in /etc/dovecot/conf.d/20-managesieve.conf to enable the sieve protocol: 

    protocols = $protocols sieve

    This setting activates Sieve in addition to the other protocols that are already enabled.

  3. Open the ManageSieve port in firewalld: 

    # firewall-cmd --permanent --add-service=managesieve
# firewall-cmd --reload

  4. Reload Dovecot: 

    # systemctl reload dovecot

Verification

  1. Use a client and upload a Sieve script. Use the following connection settings:

    • Port: 4190
    • Connection security: SSL/TLS
    • Authentication method: PLAIN
  2. Send an email to the user who has the Sieve script uploaded. If the email matches the rules in the script, verify that the server performs the defined actions.

Additional resources

  • /usr/share/doc/dovecot/wiki/Pigeonhole.Sieve.Plugins.IMAPSieve.txt
  • /usr/share/doc/dovecot/wiki/Pigeonhole.Sieve.Troubleshooting.txt
  • firewall-cmd(1) man page

11.9. How Dovecot processes configuration files

The dovecot package provides the main configuration file /etc/dovecot/dovecot.conf and multiple configuration files in the /etc/dovecot/conf.d/ directory. Dovecot combines the files to build the configuration when you start the service.

The main benefit of multiple config files is to group settings and increase readability. If you prefer a single configuration file, you can instead maintain all settings in /etc/dovecot/dovecot.conf and remove all include and include_try statements from that file.

Additional resources

  • /usr/share/doc/dovecot/wiki/ConfigFile.txt
  • /usr/share/doc/dovecot/wiki/Variables.txt

Chapter 12. Configuring printing

The Common UNIX Printing System (CUPS) manages printing on Red Hat Enterprise Linux. Users configure printers in CUPS on their host to print. Additionally, you can share printers in CUPS to use the host as a print server.

CUPS supports printing to:

  • AirPrint™ and IPP Everywhere™ printers
  • Network and local USB printers with legacy PostScript Printer Description (PPD)-based drivers

12.1. Installing and configuring CUPS

You can use CUPS to print from a local host. You can also use this host to share printers in the network and act as a print server.

Procedure

  1. Install the cups package: 

    # yum install cups

  2. If you configure a CUPS as a print server, edit the /etc/cups/cupsd.conf file, and make the following changes:

    1. If you want to remotely configure CUPS or use this host as a print server, configure on which IP addresses and ports the service listens: 

      Listen 192.0.2.1:631
Listen [2001:db8:1::1]:631

      By default, CUPS listens only on localhost interfaces (127.0.0.1 and ::1). Specify IPv6 addresses in square brackets.

      Important

      Do not configure CUPS to listen on interfaces that allow access from untrustworthy networks, such as the internet.

    2. Configure which IP ranges can access the service by allowing the respective IP ranges in the <Location /> directive: 

      <Location />
  Allow from 192.0.2.0/24
  Allow from [2001:db8:1::1]/32
  Order allow,deny
</Location>

    3. In the <Location /admin> directive, configure which IP addresses and ranges can access the CUPS administration services: 

      <Location /admin>
  Allow from 192.0.2.15/32
  Allow from [2001:db8:1::22]/128
  Order allow,deny
</Location>

      With these settings, only the hosts with the IP addresses 192.0.2.15 and 2001:db8:1::22 can access the administration services.

    4. Optional: Configure IP addresses and ranges that are allowed to access the configuration and log files in the web interface: 

      <Location /admin/conf>
  Allow from 192.0.2.15/32
  Allow from [2001:db8:1::22]/128
  ...
</Location>

<Location /admin/log>
  Allow from 192.0.2.15/32
  Allow from [2001:db8:1::22]/128
  ...
</Location>

  3. If you run the firewalld service and want to configure remote access to CUPS, open the CUPS port in firewalld: 

    # firewall-cmd --permanent --add-port=631/tcp
# firewall-cmd --reload

    If you run CUPS on a host with multiple interfaces, consider limiting the access to the required networks.

  4. Enable and start the cups service: 

    # systemctl enable --now cups

Verification

  • Use a browser, and access http://<hostname>:631. If you can connect to the web interface, CUPS works.

    Note that certain features, such as the Administration tab, require authentication and an HTTPS connection. By default, CUPS uses a self-signed certificate for HTTPS access and, consequently, the connection is not secure when you authenticate.

Next steps

12.2. Configuring TLS encryption on a CUPS server

CUPS supports TLS-encrypted connections and, by default, the service enforces encrypted connections for all requests that require authentication. If no certificates are configured, CUPS creates a private key and a self-signed certificate. This is only sufficient if you access CUPS from the local host itself. For a secure connection over the network, use a server certificate that is signed by a certificate authority (CA).

Warning

Without encryption or with a self-signed certificates, a man-in-the-middle (MITM) attack can disclose, for example:

  • Credentials of administrators when configuring CUPS using the web interface
  • Confidential data when sending print jobs over the network

Prerequisites

  • CUPS is configured.
  • You created a private key, and a CA issued a server certificate for it.
  • If an intermediate certificate is required to validate the server certificate, attach the intermediate certificate to the server certificate.
  • The private key is not protected by a password because CUPS provides no option to enter the password when the service reads the key.

  • The Canonical Name (CN) or Subject Alternative Name (SAN) field in the certificate matches one of the following:

    • The fully-qualified domain name (FQDN) of the CUPS server
    • An alias that the DNS resolves to the server’s IP address
  • The private key and server certificate files use the Privacy Enhanced Mail (PEM) format.
  • Clients trust the CA certificate.

Procedure

  1. Edit the /etc/cups/cups-files.conf file, and add the following setting to disable the automatic creation of self-signed certificates: 

    CreateSelfSignedCerts no

  2. Remove the self-signed certificate and private key: 

    # rm /etc/cups/ssl/<hostname>.crt /etc/cups/ssl/<hostname>.key

  3. Optional: Display the FQDN of the server: 

    # hostname -f
server.example.com

  4. Optional: Display the CN and SAN fields of the certificate: 

    # openssl x509 -text -in /etc/cups/ssl/server.example.com.crt
Certificate:
  Data:
    ...
    Subject: CN = server.example.com
    ...
    X509v3 extensions:
      ...
      X509v3 Subject Alternative Name:
        DNS:server.example.com
  ...

  5. If the CN or SAN fields in the server certificate contains an alias that is different from the server’s FQDN, add the ServerAlias parameter to the /etc/cups/cupsd.conf file: 

    ServerAlias alternative_name.example.com

    In this case, use the alternative name instead of the FQDN in the rest of the procedure.

  6. Store the private key and server certificate in the /etc/cups/ssl/ directory, for example: 

    # mv /root/server.key /etc/cups/ssl/server.example.com.key
# mv /root/server.crt /etc/cups/ssl/server.example.com.crt
    Important

    CUPS requires that you name the private key <fqdn>.key and the server certificate file <fqdn>.crt. If you use an alias, you must name the files <alias>.key and <alias>.crt.

  7. Set secure permissions on the private key that enable only the root user to read this file: 

    # chown root:root /etc/cups/ssl/server.example.com.key
# chmod 600 /etc/cups/ssl/server.example.com.key

    Because certificates are part of the communication between a client and the server before they establish a secure connection, any client can retrieve the certificates without authentication. Therefore, you do not need to set strict permissions on the server certificate file.

  8. Restore the SELinux context: 

    # restorecon -Rv /etc/cups/ssl/

  9. By default, CUPS enforces encrypted connections only if a task requires authentication, for example when performing administrative tasks on the /admin page in the web interface.

    To enforce encryption for the entire CUPS server, add Encryption Required to all <Location> directives in the /etc/cups/cupsd.conf file, for example: 

    <Location />
  ...
  Encryption Required
</Location>

  10. Restart CUPS: 

    # systemctl restart cups

Verification

  1. Use a browser, and access https://<hostname>:631/admin/. If the connection succeeds, you configured TLS encryption in CUPS correctly.
  2. If you configured that encryption is required for the entire server, access http://<hostname>:631/. CUPS returns an Upgrade Required error in this case.

Troubleshooting

  • Display the systemd journal entries of the cups service: 

    # journalctl -u cups

    If the journal contains an Unable to encrypt connection: Error while reading file error after you failed to connect to the web interface by using the HTTPS protocol, verify the name of the private key and server certificate file.

Additional resources

12.3. Granting administration permissions to manage a CUPS server in the web interface

By default, members of the sys, root, and wheel groups can perform administration tasks in the web interface. However, certain other services use these groups as well. For example, members of the wheel groups can, by default, execute commands with root permissions by using sudo. To avoid that CUPS administrators gain unexpected permissions in other services, use a dedicated group for CUPS administrators.

Prerequisites

  • CUPS is configured.
  • The IP address of the client you want to use has permissions to access the administration area in the web interface.

Procedure

  1. Create a group for CUPS administrators: 

    # groupadd cups-admins

  2. Add the users who should manage the service in the web interface to the cups-admins group: 

    # usermod -a -G cups-admins <username>

  3. Update the value of the SystemGroup parameter in the /etc/cups/cups-files.conf file, and append the cups-admin group: 

    SystemGroup sys root wheel cups-admins

    If only the cups-admin group should have administrative access, remove the other group names from the parameter.

  4. Restart CUPS: 

    # systemctl restart cups

Verification

  1. Use a browser, and access https://<hostname_or_ip_address>:631/admin/.

    Note

    You can access the administration area in the web UI only if you use the HTTPS protocol.

  2. Start performing an administrative task. For example, click Add printer.

  3. The web interface prompts for a username and password. To proceed, authenticate by using credentials of a user who is a member of the cups-admins group.

    If authentication succeeds, this user can perform administrative tasks.

12.4. Overview of packages with printer drivers

Red Hat Enterprise Linux (RHEL) provides different packages with printer drivers for CUPS. The following is a general overview of these packages and for which vendors they contain drivers:

Table 12.1. Driver package list

Package nameDrivers for printers

cups

Zebra, Dymo

c2esp

Kodak

foomatic

Brother, Canon, Epson, Gestetner, HP, Infotec, Kyocera, Lanier, Lexmark, NRG, Ricoh, Samsung, Savin, Sharp, Toshiba, Xerox, and others

gutenprint-cups

Brother, Canon, Epson, Fujitsu, HP, Infotec, Kyocera, Lanier, NRG, Oki, Minolta, Ricoh, Samsung, Savin, Xerox, and others

hplip

HP

pnm2ppa

HP

splix

Samsung, Xerox, and others

Note that some packages can contain drivers for the same printer vendor or model but with different functionality.

After installing the required package, you can display the list of drivers in the CUPS web interface or by using the lpinfo -m command.

12.5. Determining whether a printer supports driverless printing

CUPS supports driverless printing, which means that you can print without providing any hardware-specific software for the printer model. For this, the printer must inform the client about its capabilities and use one of the following standards:

  • AirPrint™
  • IPP Everywhere™
  • Mopria®
  • Wi-Fi Direct Print Services

You can use the ipptool utility to find out whether a printer supports driverless printing.

Prerequisites

  • The printer or remote print server supports the Internet Printing Protocol (IPP).
  • The host can connect to the IPP port of the printer or remote print server. The default IPP port is 631.

Procedure

  • Query the ipp-versions-supported and document-format-supported attributes, and ensure that get-printer-attributes test passes:

    • For a remote printer, enter: 

      # ipptool -tv ipp://<ip_address_or_hostname>:631/ipp/print get-printer-attributes.test | grep -E "ipp-versions-supported|document-format-supported|get-printer-attributes"
Get printer attributes using get-printer-attributes      [PASS]
    ipp-versions-supported (1setOf keyword) = ...
    document-format-supported (1setOf mimeMediaType) = ...

    • For a queue on a remote print server, enter: 

      # ipptool -tv ipp://<ip_address_or_hostname>:631/printers/<queue_name> get-printer-attributes.test | grep -E "ipp-versions-supported|document-format-supported|get-printer-attributes"
Get printer attributes using get-printer-attributes      [PASS]
    ipp-versions-supported (1setOf keyword) = ...
    document-format-supported (1setOf mimeMediaType) = ...

    To ensure that driverless printing works, verify in the output:

    • The get-printer-attributes test returns PASS.
    • The IPP version that the printer supports is 2.0 or higher.

    • The list of formats contains one of the following:

      • application/pdf
      • image/urf
      • image/pwg-raster
    • For color printers, the output contains one of the mentioned formats and, additionally, image/jpeg.

Next steps:

12.6. Adding a printer to CUPS by using the web interface

Before users can print through CUPS, you must add printers. You can use both network printers and printers that are directly attached to the CUPS host, for example over USB.

You can add printers by using the CUPS driverless feature or by using a PostScript Printer Description (PPD) file.

Note

CUPS prefers driverless printing, and using drivers is deprecated.

Red Hat Enterprise Linux (RHEL) does not provide the name service switch multicast DNS plug-in (nss-mdns), which resolves requests by querying an mDNS responder. Consequently, automatic discovery and installation for local driverless printers by using mDNS is not available in RHEL. To work around this problem, install single printers manually or use cups-browsed to automatically install a high amount of print queues that are available on a remote print server.

Prerequisites

Procedure

  1. Use a browser, and access https://<hostname>:631/admin/.

    You must connect to the web interface by using the HTTPS protocol. Otherwise, CUPS prevents you from authenticating in a later step for security reasons.

  2. Click Add printer.
  3. If you are not already authenticated, CUPS prompts for credentials of an administrative user. Enter the username and password of an authorized user.
  4. If you decide to not use driverless printing and the printer you want to add is detected automatically, select it, and click Continue.

  5. If the printer was not detected:

    1. Select the protocol that the printer supports.

      cups select printing protocol

      If your printer supports driverless printing and you want to use this feature, select the ipp or ipps protocol.

    2. Click Continue.

    3. Enter the URL to the printer or to the queue on a remote print server.

      cups add printer url
    4. Click Continue.

  6. Enter a name and, optionally, a description and location. If you use CUPS as a print server, and other clients should be able to print through CUPS on this printer, select also Share this printer.

    cups add printer details

  7. Select the printer manufacturer in the Make list. If the printer manufacturer is not on the list, select Generic or upload a PPD file for the printer.

    cups add printer make
  8. Click Continue.

  9. Select the printer model:

    • If the printer supports driverless printing, select IPP Everywhere. Note that, if you previously installed printer-specific drivers locally, it is possible that the list also contains entries such as <printer_name> - IPP Everywhere.
    • If the printer does not support driverless printing, select the model or upload the PPD file for the printer.
    cups add printer model
  10. Click Add Printer

  11. The settings and tabs on the Set printer options page depend on the driver and the features the printer supports. Use this page to set default options, such as for the paper size.

    cups add printer defaults
  12. Click Set default options.

Verification

  1. Open the Printers tab in the web interface.
  2. Click on the printer’s name.

  3. In the Maintenance list, select Print test page.

    cups print test page

Troubleshooting

12.7. Adding a printer to CUPS by using the lpadmin utility

Before users can print through CUPS, you must add printers. You can use both network printers and printers that are directly attached to the CUPS host, for example over USB.

You can add printers by using the CUPS driverless feature or by using a PostScript Printer Description (PPD) file.

Note

CUPS prefers driverless printing, and using drivers is deprecated.

Red Hat Enterprise Linux (RHEL) does not provide the name service switch multicast DNS plug-in (nss-mdns), which resolves requests by querying an mDNS responder. Consequently, automatic discovery and installation for local driverless printers by using mDNS is not available in RHEL. To work around this problem, install single printers manually or use cups-browsed to automatically install a high amount of print queues that are available on a remote print server.

Prerequisites

Procedure

  • Add the printer to CUPS:

    • To add a printer with driverless support, enter: 

      # lpadmin -p Demo-printer -E -v ipp://192.0.2.200/ipp/print -m everywhere

      If the -m everywhere option does not work for your printer, try -m driverless:<uri>, for example: -m driverless:ipp://192.0.2.200/ipp/print.

    • To add a queue from a remote print server with driverless support, enter: 

      # lpadmin -p Demo-printer -E -v ipp://192.0.2.201/printers/example-queue -m everywhere

      If the -m everywhere option does not work for your printer, try -m driverless:<uri>, for example: -m driverless:ipp://192.0.2.200/printers/example-queue.

    • To add a printer with a driver in file, enter: 

      # lpadmin -p Demo-printer -E -v socket://192.0.2.200/ -P /root/example.ppd

    • To add a queue from a remote print server with a driver in a file, enter: 

      # lpadmin -p Demo-printer -E -v ipp://192.0.2.201/printers/example-queue -P /root/example.ppd

    • To add a printer with a driver in the local driver database:

      1. List the drivers in the database: 

        # lpinfo -m
...
drv:///sample.drv/generpcl.ppd Generic PCL Laser Printer
...

      2. Add the printer with the URI to the driver in the database: 

        # lpadmin -p Demo-printer -E -v socket://192.0.2.200/ -m drv:///sample.drv/generpcl.ppd

    These commands uses the following options:

    • -p <printer_name>: Sets the name of the printer in CUPS.
    • -E: Enables the printer and CUPS accepts jobs for it. Note that you must specify this option after -p. See the option’s description in the man page for further details.
    • -v <uri>: Sets the URI to the printer or remote print server queue.
    • -m <driver_uri>: Sets the PPD file based on the provided driver URI obtained from the local driver database.
    • -P <PPD_file>: Sets the path to the PPD file.

Verification

  1. Display the available printers: 

    # lpstat -p
printer Demo-printer is idle. enabled since Fri 23 Jun 2023 09:36:40 AM CEST

  2. Print a test page: 

    # lp -d Demo-printer /usr/share/cups/data/default-testpage.pdf

12.8. Performing maintenance and administration tasks on CUPS printers by using the web interface

Printer administrators sometimes need to perform different tasks on a print server. For example:

  • Maintenance tasks, such as temporary pausing a printer while a technician repairs a printer
  • Administrative tasks, such as changing a printer’s default settings

You can perform these tasks by using the CUPS web interface.

Prerequisites

Procedure

  1. Use a browser, and access https://<hostname>:631/printers/.

    You must connect to the web interface by using the HTTPS protocol. Otherwise, CUPS prevents you from authenticating in a later step for security reasons.

  2. Click on the name of the printer that you want to configure.

  3. Depending on whether you want to perform a maintenance or administration task, select the required action from the corresponding list:

    cups printer actions
  4. If you are not already authenticated, CUPS prompts for credentials of an administrative user. Enter the username and password of an authorized user.
  5. Perform the task.

12.9. Using Samba to print to a Windows print server with Kerberos authentication

With the samba-krb5-printing wrapper, Active Directory (AD) users who are logged in to Red Hat Enterprise Linux (RHEL) can authenticate to Active Directory (AD) by using Kerberos and then print to a local CUPS print server that forwards the print job to a Windows print server.

The benefit of this configuration is that the administrator of CUPS on RHEL does not need to store a fixed user name and password in the configuration. CUPS authenticates to AD with the Kerberos ticket of the user that sends the print job.

Note

Red Hat supports only submitting print jobs to CUPS from your local system, and not to re-share a printer on a Samba print server.

Prerequisites

  • The printer that you want to add to the local CUPS instance is shared on an AD print server.
  • You joined the RHEL host as a member to the AD.
  • CUPS is installed on RHEL, and the cups service is running.
  • The PostScript Printer Description (PPD) file for the printer is stored in the /usr/share/cups/model/ directory.

Procedure

  1. Install the samba-krb5-printing, samba-client, and krb5-workstation packages: 

    # yum install samba-krb5-printing samba-client krb5-workstation

  2. Optional: Authenticate as a domain administrator and display the list of printers that are shared on the Windows print server: 

    # smbclient -L win_print_srv.ad.example.com -U administrator@AD_KERBEROS_REALM --use-kerberos=required

	Sharename       Type      Comment
	---------       ----      -------
	...
	Example         Printer   Example
	...

  3. Optional: Display the list of CUPS models to identify the PPD name of your printer: 

    lpinfo -m
...
samsung.ppd Samsung M267x 287x Series PXL
...

    You require the name of the PPD file when you add the printer in the next step.

  4. Add the printer to CUPS: 

    # lpadmin -p "example_printer" -v smb://win_print_srv.ad.example.com/Example -m samsung.ppd -o auth-info-required=negotiate -E

    The command uses the following options:

    • -p printer_name sets the name of the printer in CUPS.
    • -v URI_to_Windows_printer sets the URI to the Windows printer. Use the following format: smb://host_name/printer_share_name.
    • -m PPD_file sets the PPD file the printer uses.
    • -o auth-info-required=negotiate configures CUPS to use Kerberos authentication when it forwards print jobs to the remote server.
    • -E enables the printer and CUPS accepts jobs for the printer.

Verification

  1. Log into the RHEL host as an AD domain user.

  2. Authenticate as an AD domain user: 

    # kinit domain_user_name@AD_KERBEROS_REALM

  3. Print a file to the printer you added to the local CUPS print server: 

    # lp -d example_printer file

12.10. Using cups-browsed to locally integrate printers from a remote print server

The cups-browsed service uses DNS service discovery (DNS-SD) and CUPS browsing to make all or a filtered subset of shared remote printers automatically available in a local CUPS service.

For example, administrators can use this feature on workstations to make only printers from a trusted print server available in a print dialog of applications. It is also possible to configure cups-browsed to filter the browsed printers by certain criteria to reduce the number of listed printers if a print server shares a large number of printers.

Note

If the print dialog in an application uses other mechanisms than, for example DNS-SD, to list remote printers, cups-browsed has no influence. The cups-browsed service also does not prevent users from manually accessing non-listed printers.

Prerequisites

  • The CUPS service is configured on the local host.

  • A remote CUPS print server exists, and the following conditions apply to this server:

    • The server listens on an interface that is accessible from the client.
    • The Allow from parameter in the server’s <Location /> directive in the /etc/cups/cups.conf file allows access from the client’s IP address.
    • The server shares printers.
    • Firewall rules allow access from the client to the CUPS port on the server.

Procedure

  1. Edit the /etc/cups/cups-browsed.conf file, and make the following changes:

    1. Add BrowsePoll parameters for each remote CUPS server you want to poll: 

      BrowsePoll remote_cups_server.example.com
BrowsePoll 192.0.2.100:1631

      Append :<port> to the hostname or IP address if the remote CUPS server listens on a port different from 631.

    2. Optional: Configure a filter to limit which printers are shown in the local CUPS service. For example, to filter for queues whose name contain sales_, add: 

      BrowseFilter name sales_

      You can filter by different field names, negate the filter, and match the exact values. For further details, see the parameter description and examples in the cups-browsed.conf(5) man page.

    3. Optional: Change the polling interval and timeout to limit the number of browsing cycles: 

      BrowseInterval 1200
BrowseTimeout 6000

      Increase both BrowseInterval and BrowseTimeout in the same ratio to avoid situations in which printers disappear from the browsing list. This mean, multiply the value of BrowseInterval by 5 or a higher integer, and use this result value for BrowseTimeout.

      By default, cups-browsed polls remote servers every 60 seconds and the timeout is 300 seconds. However, on print servers with many queues, these default values can cost many resources.

  2. Enable and start the cups-browsed service: 

    # systemctl enable --now cups-browsed

Verification

  • List the available printers: 

    # lpstat -v
device for Demo-printer: implicitclass://Demo-printer/
...

    If the output for a printer contains implicitclass, cups-browsed manages the printer in CUPS.

Additional resources

  • cups-browsed.conf(5) man page

12.11. Accessing the CUPS logs in the systemd journal

By default, CUPS stores log messages in the systemd journal. This includes:

  • Error messages
  • Access log entries
  • Page log entries

Prerequisites

Procedure

  • Display the log entries:

    • To display all log entries, enter: 

      # journalctl -u cups

    • To display the log entries for a specific print job, enter: 

      # journalctl -u cups JID=<print_job_id>

    • To display log entries within a specific time frame, enter: 

      # journalectl -u cups --since=<YYYY-MM-DD> --until=<YYYY-MM-DD>

      Replace YYYY with the year, MM with the month, and DD with the day.

Additional resources

  • journalctl(1) man page

12.12. Configuring CUPS to store logs in files instead of the systemd journal

By default, CUPS stores log messages in the systemd journal. Alternatively, you can configure CUPS to store log messages in files.

Prerequisites

Procedure

  1. Edit the /etc/cups/cups-files.conf file, and set the AccessLog, ErrorLog, and PageLog parameters to the paths where you want to store these log files: 

    AccessLog /var/log/cups/access_log
ErrorLog /var/log/cups/error_log
PageLog /var/log/cups/page_log

  2. If you configure CUPS to store the logs in a directory other than /var/log/cups/, set the cupsd_log_t SELinux context on this directory, for example: 

    # semanage fcontext -a -t cupsd_log_t "/var/log/printing(/.*)?"
# restorecon -Rv /var/log/printing/

  3. Restart the cups service: 

    # systemctl restart cups

Verification

  1. Display the log files: 

    # cat /var/log/cups/access_log
# cat /var/log/cups/error_log
# cat /var/log/cups/page_log

  2. If you configured CUPS to store the logs in a directory other than /var/log/cups/, verify that the SELinux context on the log directory is cupsd_log_t: 

    # ls -ldZ /var/log/printing/
drwxr-xr-x. 2 lp sys unconfined_u:object_r:cupsd_log_t:s0 6 Jun 20 15:55 /var/log/printing/

12.13. Accessing the CUPS documentation

CUPS provides browser-based access to the service’s documentation that is installed on the CUPS server. This documentation includes:

  • Administration documentation, such as for command-line printer administration and accounting
  • Man pages
  • Programming documentation, such as the administration API
  • References
  • Specifications

Prerequisites

Procedure

  1. Use a browser, and access http://<hostname_or_ip_address>:631/help/:

    cups help
  2. Expand the entries in Online Help Documents, and select the documentation you want to read.

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