`autofs` Common Tasks

Overriding or augmenting site configuration files

It can be useful to override site defaults for a specific mount point on a client system. For example, assuming that the automounter maps are stored in NIS and the /etc/nsswitch.conf file has the following directive:

automount:  files nis

and the NIS auto.master map file contains the following:

/home auto.home

Also assume the NIS auto.home map contains the following:

beth     fileserver.example.com:/export/home/beth
joe      fileserver.example.com:/export/home/joe
*        fileserver.example.com:/export/home/&

and the file map /etc/auto.home does not exist.

For the above example, lets assume that the client system needs to mount home directories from a different server. In this case, the client will need to use the following /etc/auto.master map:

/home /etc/auto.home2
+auto.master

And the /etc/auto.home2 map contains the entry:

*   labserver.example.com:/export/home/&

Because only the first occurrence of a mount point is processed, /home will contain the contents of /etc/auto.home2 instead of the NIS auto.home map.

Alternatively, if you just want to augment the site-wide auto.home map with a few entries, create a /etc/auto.home file map, and in it put your new entries and at the end, include the NIS auto.home map. Then the /etc/auto.home file map might look similar to:

mydir someserver:/export/mydir
+auto.home

Given the NIS auto.home map listed above, an ls of /home would now give:

~]$ ls /home
beth  joe  mydir

This last example works as expected because autofs knows 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 nsswitch configuration.

Using LDAP to Store Automounter Maps

LDAP client libraries must be installed on all systems which are to retrieve automounter maps from LDAP. On RHEL 5, the openldap package 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.

The most recently established schema for storing automount maps in LDAP is described by rfc2307bis. To use this schema it is necessary to set it in the autofs configuration (/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"

Ensure that these are the only schema entries not commented in the configuration. Please also note that the automountKey replaces the cn attribute in the rfc2307bis schema. An LDIF of 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/&

Adapting Autofs v4 Maps To Autofs v5

v4 Multi-map entries

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> -- ...

Any number of maps can be combined into a single map in this manner. This feature is no longer present in v5. This is because Version 5 supports included maps which can be used to attain the same results. Consider the following multi-map example:

/home file /etc/auto.home -- nis auto.home

This can be replaced by the following configuration for v5:

/etc/nsswitch.conf must list:

automount: files nis

/etc/auto.master should contain:

/home  auto.home

/etc/auto.home should contain:

<entries for the home directory>
+auto.home

In this way, the entries from /etc/auto.home and the nis auto.home map are combined.

Multiple master maps

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 auto.master map.

In version 5, this is no longer the behaviour. Only the first master map found from the list of sources in nsswitch.conf is 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

The above configuration will merge the contents of the file-based auto.master and 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.master and an LDAP auto.master.

This limitation can be overcome by creating a master maps that have a different name in the source. In the example above if we had an LDAP master map named auto.master.ldap we 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.