Chapter 5. Accessing the desktop remotely

You can connect to the desktop on a RHEL server from a remote client.

5.1. Remote desktop access options

RHEL provides several options for remotely connecting to the desktop. Each option fits a different use case:

Single-user access using GNOME tools

This method enables remote access on the client and the server using graphical GNOME applications. It configures a Virtual Network Computing (VNC) session so that only a single user can connect to the desktop on the server at a given time.

Depending on the session type, this method uses different components to implement screen sharing:

  • In an X11 session, it uses the vino component.
  • In a Wayland session, it uses the gnome-remote-desktop component.

    This method always uses display number 0. As a consequence, the VNC session always connects to the user who is logged into the server system.

    The VNC client application must support tls_anon connections. For example, you can use the Remote Desktop Viewer (vinagre) application on Linux systems. Before you can connect from Microsoft Windows clients, such as RealVNC, you must disable the VNC encryption on the server.

Multi-user access using command-line tools

This method configures a VNC session so that multiple remote clients can connect to the server in parallel. You must first enable the VNC access on the client and the server using command-line tools.

Any VNC client application can connect to a server configured using this method.

Accessing a single application using X11 forwarding over SSH

This method executes an SSH command on the client that launches an individual graphical on the server. The application window opens on the client.

This method is useful when you do not require a full remote desktop session.

5.2. Remotely accessing the desktop as a single user

You can remotely connect to the desktop on a RHEL server using graphical GNOME applications. Only a single user can connect to the desktop on the server at a given time.

5.2.1. Enabling desktop sharing on the server using GNOME

This procedure configures a RHEL server to enable a remote desktop connection from a single client.

Procedure

  1. Configure a firewall rule to enable VNC access to the server:

    # firewall-cmd --permanent --add-service=vnc-server
  2. Reload firewall rules:

    # firewall-cmd --reload
  3. Open Settings in GNOME.
  4. Navigate to the Sharing menu:

    screen sharing 0

  5. Click Screen Sharing.

    The screen sharing configuration opens:

    screen sharing 1 off

  6. Click the switch button in the window header to enable screen sharing:

    screen sharing 2 on highlight

  7. Select the Allow connections to control the screen check box.
  8. Under Access Options, select the Require a password option.
  9. Set a password in the Password field.

    Remote clients must enter this password when connecting to the desktop on the server.

    screen sharing 4 password

5.2.2. Connecting to a shared desktop using GNOME

This procedure connects to a remote desktop session using the Remote Desktop Viewer application. It connects to the graphical session of the user that is currently logged in on the server.

Prerequisites

Procedure

  1. Install the Remote Desktop Viewer application on the client:

    # yum install vinagre
  2. Launch the Remote Desktop Viewer application.
  3. Click Connect.

    vinagre connect

  4. In the Protocol menu, select VNC.
  5. In the Host field, enter the IP address of the server.

    vinagre vnc

  6. Click Connect.

Verification steps

  1. On the client, check that you can see the shared server desktop.
  2. On the server, a screen sharing indicator appears on the right side of the top panel:

    screen sharing indicator

    You can control the screen sharing in the system menu.

5.2.3. Disabling encryption in GNOME VNC

You can disable encryption in the GNOME remote desktop solution. This enables VNC clients that do not support the encryption to connect to the server.

Procedure

  1. As the server user, set the /org/gnome/desktop/remote-desktop/vnc/encryption GSettings key to ['none']:

    $ gsettings set org.gnome.desktop.remote-desktop.vnc encryption "['none']"
  2. Optional: Red Hat recommends that you tunnel the VNC connection over SSH to your VNC port. As a result, the SSH tunnel keeps the connection encrypted.

    For example:

    1. On the client, configure the port forwarding:

      # ssh -N -T -L 5901:server-ip-address:5901
    2. Connect to the VNC session on the localhost:5901 address.

5.3. Remotely accessing the desktop as multiple users

You can remotely connect to the desktop on a RHEL server and open multiple sessions as different users at the same time.

5.3.1. The mapping of port and display numbers to users in VNC

With VNC, the client can connect to the desktop sessions of different users on the server. A display number and a TCP port number are attached to each server user that exports a VNC session. The client uses the port number to specify which server user it connects to.

If several clients connect using the same port number, they all open a VNC session to the same server user.

You must configure a mapping for each server user that exports a VNC session. For every such user, you must pick a unique port and display number.

The recommended mapping

Red Hat recommends that you start with port number 5902 and display number 2 for the first user, and increment the numbers by one for each additional server user.

Port number 5900 and display number 0 represent the server user that is currently logged into the graphical session. You cannot start a VNC server for the user who is already logged into the graphical session.

Table 5.1. Port and display number pairs

Port numberDisplay numberNote

5900

0

The logged-in user

5901

1

 

5902

2

The first recommended VNC user

5903

3

 

 
Important

Red Hat recommends that you do not configure the root user to export a VNC session. A root VNC session is unsafe and certain elements of the session might not work as expected.

Firewall rules

You must open the selected ports in your firewall configuration. Allowing the vnc-server service in your firewall opens ports from 5900 to 5903. If you need to enable access to additional server users, you must open ports above 5903 by manually specifying the port numbers.

5.3.2. VNC server configuration files

Several configuration files affect the behavior of the VNC server. You can configure the user mapping and various global options.

General options

You can configure general options of the VNC server in the /etc/tigervnc/vncserver-config-defaults configuration file. The file uses the following format:

option1=value
option2

For example:

session=gnome
alwaysshared
securitytypes=vncauth,tlsvnc
desktop=sandbox
geometry=2000x1200

The priority of configuration files

The VNC server reads the following files for general options, in order from most important to least important:

  1. /etc/tigervnc/vncserver-config-mandatory

    This file replaces the default configuration and has a higher priority than the per-user configuration. It is intended for system administrators who want to enforce particular VNC options.

  2. $HOME/.vnc/config

    Individual users can override the default VNC configuration in this file.

  3. /etc/tigervnc/vncserver-config-defaults

    This file stores the default VNC configuration.

User mapping

You can configure the mapping between users and their associated port and display numbers in the /etc/tigervnc/vncserver.users configuration file. The file uses the following format:

:number=user

For example:

:2=test
:3=vncuser

Additional resources

  • For a list of available configuration options, see the Xvnc(1) man page.

5.3.3. Enabling multi-user VNC access on the server

This procedure configures a RHEL server so that multiple users can open VNC sessions on it at the same time.

Prerequisites

  • If you previously configured VNC using systemd unit files, remove any outdated VNC configuration:

    [root]# rm /etc/systemd/system/vncserver@.service

Procedure

  1. Install the VNC server:

    [root]# yum install tigervnc-server
  2. Map users to display and port numbers.

    In the /etc/tigervnc/vncserver.users configuration file, add a line for each server user that will export a VNC session:

    :user-number=user-name
    • Replace user-number with the port and display number mapped to the selected existing user.
    • Replace user-name with the user name of the selected existing user.

    For example:

    :2=vncuser
  3. Open TCP ports 5900 to 5903 in the firewall:

    [root]# firewall-cmd --permanent --add-service=vnc-server
  4. Reload the firewall rules:

    [root]# firewall-cmd --reload
  5. Add the following lines to the /etc/tigervnc/vncserver-config-defaults configuration file:

    session=gnome
    alwaysshared

    This configuration has the following effects:

    • The VNC server starts the GNOME session when a remote user logs in.
    • Multiple users can connect to the VNC server at the same time.
  6. As each server user that exports a VNC session, set the VNC password for the user:

    [regular-user]$ vncpasswd

    Remote clients must enter this password when connecting to the desktop on the server.

  7. If you previously configured VNC for the user, ensure that the configuration files have the correct SELinux context:

    [regular-user]$ restorecon -RFv ~/.vnc
  8. Enable and start the VNC server unit for the regular user:

    [root]# systemctl enable --now vncserver@:user-number
  9. If the server uses the proprietary Nvidia driver, disable Wayland:

    1. Uncomment the WaylandEnable=False line in the /etc/gdm/custom.conf configuration file.
    2. Add the DefaultSession=gnome-xorg.desktop option to the [daemon] section of the configuration file.
    3. Reboot the server.

Additional resources

5.3.4. Connecting to the VNC server as multiple users

This procedure connects to a remote desktop session using the vncviewer application. You can open multiple connections to the remote desktop at the same time.

Prerequisites

Procedure

  1. Install the VNC client:

    # yum install tigervnc
  2. Connect to the VNC server:

    $ vncviewer --shared server-ip:display
    • Replace server-ip with the IP address of the server that you are connecting to.
    • Replace display with the display number where the server user exports the VNC session.

5.4. Remotely accessing an individual application

You can remotely launch a graphical application on a RHEL server and use it from the remote client.

5.4.1. Enabling X11 forwarding on the server

This procedure configures a RHEL server so that remote clients can use graphical applications on the server over SSH.

Procedure

  1. Install basic X11 packages:

    # yum install xorg-x11-xauth xorg-x11-fonts-\* xorg-x11-utils dbus-x11
    Note

    Your applications might rely on additional graphical libraries.

  2. Check that the X11Forwarding option is enabled in the /etc/sshd/sshd_config configuration file:

    X11Forwarding yes

    The option is enabled by default in RHEL. Your organization might have disabled it.

  3. Restart the sshd service:

    # systemctl restart sshd.service

5.4.2. Launching an application remotely using X11 forwarding

This procedure accesses a graphical application on a RHEL server from a remote client using SSH.

Prerequisites

  • X11 forwarding over SSH is enabled on the server. For details, see Section 5.4.1, “Enabling X11 forwarding on the server”.
  • Ensure that an X11 display server is running on your system:

    • On RHEL, X11 is available by default in the graphical interface.
    • On Microsoft Windows, install an X11 server such as Xming.
    • On macOS, install the XQuartz X11 server.

Procedure

  1. Log in to the server using SSH:

    [local-user]$ ssh -X -Y remote-server
  2. Launch the application from the command line:

    [remote-user]$ application-binary