Autofs Maps

Autofs uses three types of maps:

• Master map

• Direct maps

• Indirect maps

Master Autofs Map

The auto_master map associates a directory with a map. The map is a master list that specifies all the maps that autofs should check. The following example shows what an auto_master file could contain.

Example 3-3 Sample /etc/auto_master File

# Master map for automounter 
# 
+auto_master 
/net            -hosts           -nosuid,nobrowse 
/home           auto_home        -nobrowse 
/nfs4           -fedfs           -ro,nosuid,nobrowse
/-              auto_direct      -ro  

This example shows the generic auto_master file with one addition for the auto_direct map. Each line in the master map /etc/auto_master has the following syntax:

mount-point map-name [ mount-options ]

mount-point

mount-point is the full (absolute) path name of a directory. If the directory does not exist, autofs creates the directory if possible. If the directory exists and is not empty, mounting on the directory hides its contents. In this situation, autofs issues a warning.

The notation /- as a mount point indicates that this particular map is a direct map. The notation also means that no particular mount point is associated with the map.

map-name

map-name is the map autofs uses to find directions to locations, or mount information. If the name is preceded by a slash (/), autofs interprets the name as a local file. Otherwise, autofs searches for the mount information by using the search that is specified in the name-service switch configuration file (/etc/nsswitch.conf). Special maps are also used for /net. See Mount Point /net for more information.

mount-options

mount-options is an optional, comma-separated list of options that apply to the mounting of the entries that are specified in map-name, unless the entries in map-name list other options. Options for each specific type of file system are listed in the mount man page for that file system. For example, see the mount_nfs(1M) man page for NFS-specific mount options. For NFS-specific mount points, the bg (background) and fg (foreground) options do not apply.

A line that begins with # is a comment. All the text that follows until the end of the line is ignored.

To split long lines into shorter ones, put a backslash (\) at the end of the line. The maximum number of characters of an entry is 1024.

Mount Point /home

The mount point /home is the directory under which the entries that are listed in /etc/auto_home (an indirect map) are to be mounted.

Mount Point /net

Autofs mounts under the directory /net all the entries in the special map -hosts. The map is a built-in map that uses only the hosts database. Suppose that the computer gumbo is in the hosts database and it exports any of its file systems. The following command changes the current directory to the root directory of the computer gumbo.

% cd /net/gumbo

Autofs can mount only the exported file systems of host gumbo, that is, those file systems on a server that are available to network users instead of those file systems on a local disk. Therefore, all the files and directories on gumbo might not be available through /net/gumbo.

With the /net method of access, the server name is in the path and is location dependent. If you want to move an exported file system from one server to another, the path might no longer work. Instead, you should set up an entry in a map specifically for the file system you want rather than use /net.

Mount Point /nfs4

The /nfs4 mount point uses a pseudo-map to mount the Federated File System domain root. A reference to /nfs4/example.net will result in an attempt to find the domain root for the DNS domain example.net and mount it at that location. This requires that the DNS server returns a record as described in Setting up a DNS Record for a FedFS Server.

Direct Autofs Maps

A direct map is an automount point. With a direct map, a direct association exists between a mount point on the client and a directory on the server. Direct maps have a full path name and indicate the relationship explicitly. The following is a typical /etc/auto_direct map:

/usr/local          -ro \
   /bin                   ivy:/export/local/sun4 \
   /share                 ivy:/export/local/share \
   /src                   ivy:/export/local/src
/usr/man            -ro   oak:/usr/man \
                          rose:/usr/man \
                          willow:/usr/man 
/usr/games          -ro   peach:/usr/games 
/usr/spool/news     -ro   pine:/usr/spool/news \
                          willow:/var/spool/news 

Lines in direct maps have the following syntax:

key [ mount-options ] location

key

key is the path name of the mount point in a direct map.

mount-options

mount-options is the options that you want to apply to this particular mount. These options are required only if the options differ from the map default. Options for each specific type of file system are listed in the mount man page for that file system. For example, see the mount_nfs(1M) man page for NFS specific mount options.

location

location is the location of the file system. One or more file systems are specified as server:pathname for NFS file systems.

---

Note - The pathname should not include an automounted mount point. The pathname should be the actual absolute path to the file system. For instance, the location of a home directory should be listed as server:/export/home/username, not as server:/home/username.

---

As in the master map, a line that begins with # is a comment. All the text that follows until the end of the line is ignored. Put a backslash at the end of the line to split long lines into shorter ones.

Of all the maps, the entries in a direct map most closely resemble the corresponding entries in /etc/vfstab. An entry might appear in /etc/vfstab as follows:

dancer:/usr/local - /usr/local/tmp nfs - yes ro 

The equivalent entry appears in a direct map as follows:

/usr/local/tmp     -ro     dancer:/usr/local

See How Autofs Selects the Nearest Read-Only Files for Clients (Multiple Locations) for other important features that are associated with this type of map.

Mount Point /-

In Example 3-3, the mount point /- tells autofs not to associate the entries in auto_direct with any specific mount point. Indirect maps use mount points that are defined in the auto_master file. Direct maps use mount points that are specified in the named map. Remember, in a direct map the key, or mount point, is a full path name.

An NIS auto_master file can have only one direct map entry because the mount point must be a unique value in the namespace. An auto_master file that is a local file can have any number of direct map entries if entries are not duplicated.

Indirect Autofs Maps

An indirect map uses a substitution value of a key to establish the association between a mount point on the client and a directory on the server. Indirect maps are useful for accessing specific file systems, such as home directories. The auto_home map is an example of an indirect map.

Lines in indirect maps have the following general syntax:

key [ mount-options ] location

key

key is a simple name without slashes in an indirect map.

mount-options

mount-options is the options that you want to apply to this particular mount. These options are required only if the options differ from the map default. Options for each specific type of file system are listed in the mount man page for that file system. For example, see the mount_nfs(1M) man page for NFS-specific mount options.

location

location is the location of the file system. One or more file systems are specified as server:pathname.

---

Note - The pathname should not include an automounted mount point. The pathname should be the actual absolute path to the file system. For instance, the location of a directory should be listed as server:/usr/local, not as server:/net/server/usr/local.

---

As in the master map, a line that begins with # is a comment. All the text that follows until the end of the line is ignored. Put a backslash (\) at the end of the line to split long lines into shorter ones. Example 3-3 shows an auto_master map that contains the following entry:

/home      auto_home        -nobrowse    

auto_home is the name of the indirect map that contains the entries to be mounted under /home. A typical auto_home map might contain the following:

david                  willow:/export/home/david
rob                    cypress:/export/home/rob
gordon                 poplar:/export/home/gordon
rajan                  pine:/export/home/rajan
tammy                  apple:/export/home/tammy
jim                    ivy:/export/home/jim
linda    -rw,nosuid    peach:/export/home/linda

As an example, assume that the previous map is on host oak. Suppose that the user linda has an entry in the password database that specifies her home directory as /home/linda. Whenever linda logs in to computer oak, autofs mounts the directory /export/home/linda that resides on the computer peach. Her home directory is mounted read-write, nosuid.

Assume the following conditions occur: User linda's home directory is listed in the password database as /home/linda. Anybody, including Linda, has access to this path from any computer that is set up with the master map referring to the map in the previous example.

Under these conditions, user linda can run login or rlogin on any of these computers and have her home directory mounted in place for her.

Furthermore, now Linda can also type the following command:

% cd ~david

autofs mounts David's home directory for her (if all permissions allow).

On a network without a name service, you have to change all the relevant files (such as /etc/passwd) on all systems on the network to allow Linda access to her files. With NIS, make the changes on the NIS master server and propagate the relevant databases to the slave servers.