/etc/fstabis that, regardless of how infrequently a user accesses the NFS mounted file system, the system must dedicate resources to keep the mounted file system in place. This is not a problem with one or two mounts, but when the system is maintaining mounts to many systems at one time, overall system performance can be affected. An alternative to
/etc/fstabis to use the kernel-based automount utility. An automounter consists of two components. One is a kernel module that implements a file system, while the other is a user-space daemon that performs all of the other functions. The automount utility can mount and unmount NFS file systems automatically (on demand mounting) therefore saving system resources. The automount utility can be used to mount other file systems including AFS, SMBFS, CIFS and local file systems.
/etc/auto.master(master map) as its default primary configuration file. This can be changed to use another supported network source and name using the autofs configuration (in
/etc/sysconfig/autofs) in conjunction with the Name Service Switch mechanism. An instance of the version 4 daemon was run for each mount point configured in the master map and so it could be run manually from the command line for any given mount point. This is not possible with version 5 because it uses a single daemon to manage all configured mount points, so all automounts must be configured in the master map. This is in line with the usual requirements of other industry standard automounters. Mount point, hostname, exported directory, and options can all be specified in a set of files (or other supported network sources) rather than configuring them manually for each host. Please ensure that you have the
autofspackage installed if you wish to use this service.
21.3.1. What's new in
autofs version 5?
- Direct map support
- Autofs direct maps provide a mechanism to automatically mount file systems at arbitrary points in the file system hierarchy. A direct map is denoted by a mount point of "/-" in the master map. Entries in a direct map contain an absolute path name as a key (instead of the relative path names used in indirect maps).
- Lazy mount and unmount support
- Multimount map entries describe a hierarchy of mount points under a single key. A good example of this is the "-hosts" map, commonly used for automounting all exports from a host under "
/net/<host>" as a multi-mount map entry. When using the "
-hosts" map, an '
ls' of "
/net/<host>" will mount autofs trigger mounts for each export from
<host>and mount and expire them as they are accessed. This can greatly reduce the number of active mounts needed when accessing a server with a large number of exports.
- Enhanced LDAP support
- The Lightweight Directory Access Protocol, or LDAP, support in autofs version 5 has been enhanced in several ways with respect to autofs version 4. The autofs configuration file (
/etc/sysconfig/autofs) provides a mechanism to specify the autofs schema that a site implements, thus precluding the need to determine this via trial and error in the application itself. In addition, authenticated binds to the LDAP server are now supported, using most mechanisms supported by the common LDAP server implementations. A new configuration file has been added for this support:
/etc/autofs_ldap_auth.conf. The default configuration file is self-documenting, and uses an XML format.
- Proper use of the Name Service Switch (
- The Name Service Switch configuration file exists to provide a means of determining from where specific configuration data comes. The reason for this configuration is to allow administrators the flexibility of using the back-end database of choice, while maintaining a uniform software interface to access the data. While the version 4 automounter is becoming increasingly better at handling the name service switch configuration, it is still not complete. Autofs version 5, on the other hand, is a complete implementation. See the manual page for nsswitch.conf for more information on the supported syntax of this file. Please note that not all nss databases are valid map sources and the parser will reject ones that are invalid. Valid sources are files, yp, nis, nisplus, ldap and hesiod.
- Multiple master map entries per autofs mount point
- One thing that is frequently used but not yet mentioned is the handling of multiple master map entries for the direct mount point "/-". The map keys for each entry are merged and behave as one map.An example is seen in the connectathon test maps for the direct mounts below:
/- /tmp/auto_dcthon /- /tmp/auto_test3_direct /- /tmp/auto_test4_direct
/etc/auto.master, also referred to as the master map which may be changed as described in the introduction section above. The master map lists autofs-controlled mount points on the system, and their corresponding configuration files or network sources known as automount maps. The format of the master map is as follows:
<mount-point> <map-name> <options>
mount-pointis the autofs mount point such as
map-nameis the name of a map source which contains a list of mount points, and the file system location from which those mount points should be mounted. The syntax for a map entry is described below.
optionsif supplied, will apply to all entries in the given map provided they don't themselves have options specified. This behavior is different from autofs version 4 where the options where cumulative. This has been changed to meet our primary goal of mixed environment compatibility.
cat /etc/auto.master/home /etc/auto.misc
<mount-point> [<options>] <location>
<mount-point>is the autofs mount point. This can be a single directory name for an indirect mount or the full path of the mount point for direct mounts. Each direct and indirect map entry key (
<mount-point>above) may be followed by a space separated list of offset directories (sub directory names each beginning with a "/") making them what is known as a mutli-mount entry.
- <options> if supplied, are the mount options for the map entries that do not specify their own options.
- <location> is the file system location such as a local file system path (preceded with the Sun map format escape character ":" for map names beginning with "/"), an NFS file system or other valid file system location.
cat /etc/auto.miscpayroll -fstype=nfs personnel:/dev/hda3 sales -fstype=ext3 :/dev/hda4
payrollfrom the server called
personnel). The second column indicates the options for the autofs mount while the third column indicates the source of the mount. Following the above configuration, the autofs mount points will be
-fstype=option is often omitted and is generally not needed for correct operation.
service autofs start
service autofs restart
/home/payroll/2006/July.sxc, the automount daemon automatically mounts the directory. If a timeout is specified, the directory will automatically be unmounted if the directory is not accessed for the timeout period.
autofs Common Tasks
188.8.131.52. Overriding or augmenting site configuration files
/etc/nsswitch.conffile has the following directive:
automount: files nis
auto.mastermap file contains the following:
auto.homemap contains the following:
beth fileserver.example.com:/export/home/beth joe fileserver.example.com:/export/home/joe * fileserver.example.com:/export/home/&
/etc/auto.homedoes not exist.
/home /etc/auto.home2 +auto.master
/etc/auto.home2map contains the entry:
/homewill contain the contents of
/etc/auto.home2instead of the NIS
auto.homemap with a few entries, create a
/etc/auto.homefile map, and in it put your new entries and at the end, include the NIS auto.home map. Then the
/etc/auto.homefile map might look similar to:
mydir someserver:/export/mydir +auto.home
auto.homemap listed above, an
/homewould now give:
ls /homebeth joe mydir
autofsknows not to include the contents of a file map of the same name as the one it is reading and so moves on to the next map source in the
184.108.40.206. Using LDAP to Store Automounter Maps
openldappackage should be installed automatically as a dependency of the
automounter. To configure LDAP access, modify
/etc/openldap/ldap.conf. Ensure that BASE and URI are set appropriately for your site. Please also ensure that the schema is set in the configuration.
rfc2307bis. To use this schema it is necessary to set it in the
/etc/sysconfig/autofs) by removing the comment characters from the schema definition. For example:
DEFAULT_MAP_OBJECT_CLASS="automountMap" DEFAULT_ENTRY_OBJECT_CLASS="automount" DEFAULT_MAP_ATTRIBUTE="automountMapName" DEFAULT_ENTRY_ATTRIBUTE="automountKey" DEFAULT_VALUE_ATTRIBUTE="automountInformation"
cnattribute in the
LDIFof a sample configuration is described below:
# extended LDIF # # LDAPv3 # base <> with scope subtree # filter: (&(objectclass=automountMap)(automountMapName=auto.master)) # requesting: ALL # # auto.master, example.com dn: automountMapName=auto.master,dc=example,dc=com objectClass: top objectClass: automountMap automountMapName: auto.master # extended LDIF # # LDAPv3 # base <automountMapName=auto.master,dc=example,dc=com> with scope subtree # filter: (objectclass=automount) # requesting: ALL # # /home, auto.master, example.com dn: automountMapName=auto.master,dc=example,dc=com objectClass: automount cn: /home automountKey: /home automountInformation: auto.home # extended LDIF # # LDAPv3 # base <> with scope subtree # filter: (&(objectclass=automountMap)(automountMapName=auto.home)) # requesting: ALL # # auto.home, example.com dn: automountMapName=auto.home,dc=example,dc=com objectClass: automountMap automountMapName: auto.home # extended LDIF # # LDAPv3 # base <automountMapName=auto.home,dc=example,dc=com> with scope subtree # filter: (objectclass=automount) # requesting: ALL # # foo, auto.home, example.com dn: automountKey=foo,automountMapName=auto.home,dc=example,dc=com objectClass: automount automountKey: foo automountInformation: filer.example.com:/export/foo # /, auto.home, example.com dn: automountKey=/,automountMapName=auto.home,dc=example,dc=com objectClass: automount automountKey: / automountInformation: filer.example.com:/export/&
220.127.116.11. Adapting Autofs v4 Maps To Autofs v5
Autofs version 4 introduced the notion of a multi-map entry in the master map. A multi-map entry is of the form:
<mount-point> <maptype1> <mapname1> <options1> -- <maptype2> <mapname2> <options2> -- ...
/home file /etc/auto.home -- nis auto.home
automount: files nis
<entries for the home directory> +auto.home
/etc/auto.homeand the nis
auto.homemap are combined.
In autofs version 4, it is possible to merge the contents of master maps from each source, such as files, nis, hesiod, and LDAP. The version 4 automounter looks for a master map for each of the sources listed in
/etc/nsswitch.conf. The map is read if it exists and its contents are merged into one large
nsswitch.confis consulted. If it is desirable to merge the contents of multiple master maps, included maps can be used. Consider the following example:
/etc/nsswitch.conf: automount: files nis
/etc/auto.master: /home /etc/auto.home +auto.master
auto.masterand the NIS-based
auto.master. However, because included map entries are only allowed in file maps, there is no way to include both an NIS
auto.masterand an LDAP
auto.master.ldapwe could also add
"+auto.master.ldap"to the file based master map and provided that "
ldap" is listed as a source in our nsswitch configuration it would also be included.