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Man Pages

Manual Reference Pages  -  AUTO_MASTER (5)


auto_master - auto_master and map file format


Auto_master Syntax
Map Syntax
Special Maps
Executable Maps
Indirect Versus Direct Maps
Directory Services
See Also


The automounter configuration consists of the auto_master configuration file, which assigns filesystem paths to map names, and maps, which contain actual mount information. The auto_master configuration file is used by the automount(8) command. Map files are read by the automountd(8) daemon.


The auto_master file consists of lines with two or three entries separated by whitespace and terminated by newline character:

 mountpoint map_name [-options]

mountpoint is either a fully specified path, or /-. When mountpoint is a full path, map_name must reference an indirect map. Otherwise, map_name must reference a direct map. See MAP SYNTAX below.

map_name specifies map to use. If map_name begins with -, it specifies a special map. See MAP SYNTAX below. If map_name is not a fully specified path (it does not start with /), automountd(8) will search for that name in /etc. Otherwise it will use the path as given. If the file indicated by map_name is executable, automountd(8) will assume it is an executable map. See MAP SYNTAX below. Otherwise, the file is opened and the contents parsed.

-options is an optional field that starts with - and can contain generic filesystem mount options.

The following example specifies that the /etc/auto_example indirect map will be mounted on /example.

/example auto_example


Map files consist of lines with a number of entries separated by whitespace and terminated by newline character:


In most cases, it can be simplified to:


key is the path component used by automountd(8) to find the right map entry to use. It is also used to form the final mountpoint. A wildcard (‘*’) can be used for the key. It matches every directory that does not match other keys. Those directories will not be visible to the user until accessed.

The options field, if present, must begin with -. When mounting the filesystem, options supplied to auto_master and options specified in the map entry are concatenated together. The special option fstype is used to specify filesystem type. It is not passed to the mount program as an option. Instead, it is passed as an argument to mount -t. The default fstype is nfs’. The special option nobrowse is used to disable creation of top-level directories for special and executable maps.

The optional mountpoint field is used to specify multiple mount points for a single key.

The location field specifies the filesystem to be mounted. Ampersands (‘&’) in the location field are replaced with the value of key. This is typically used with wildcards, like:


The location field may contain references to variables, like:


Defined variables are:

ARCH Expands to the output of uname -p.
CPU Same as ARCH.
HOST Expands to the output of uname -n.
OSNAME Expands to the output of uname -s.
OSREL Expands to the output of uname -r.
OSVERS Expands to the output of uname -v.

Additional variables can be defined with the -D option of automount(8) and automountd(8).

To pass a location that begins with /, prefix it with a colon. For example, :/dev/cd0.

This example, when put into /etc/auto_example, and with auto_master referring to the map as described above, specifies that the NFS share will be mounted on /example/x/ when any process attempts to access that mountpoint, with intr and nfsv4 mount options, described in mount_nfs(8):

x -intr,nfsv4

Automatically mount an SMB share on access, as a guest user, without prompting for a password:

share -fstype=smbfs,-N ://@server/share

Automatically mount the CD drive on access:

cd -fstype=cd9660 :/dev/cd0


Special maps have names beginning with -. Supported special maps are:

  Query the remote NFS server and map exported shares. This map is traditionally mounted on /net. Access to files on a remote NFS server is provided through the /net/ nfs-server-ip / share-name Ns/ directory without any additional configuration. Directories for individual NFS servers are not present until the first access, when they are automatically created.
  Query devices that are not yet mounted, but contain valid filesystems. Generally used to access files on removable media.
  Mount filesystems configured in fstab(5) as "noauto". This needs to be set up as a direct map.
-null Prevent automountd(8) from mounting anything on the mountpoint.

It is possible to add custom special maps by adding them, as executable maps named special_foo, to the /etc/autofs/ directory.


If the map file specified in auto_master has the execute bit set, automountd(8) will execute it and parse the standard output instead of parsing the file contents. When called without command line arguments, the executable is expected to output a list of available map keys separated by newline characters. Otherwise, the executable will be called with a key name as a command line argument. Output from the executable is expected to be the entry for that key, not including the key itself.


Indirect maps are referred to in auto_master by entries with a fully qualified path as a mount point, and must contain only relative paths as keys. Direct maps are referred to in auto_master by entries with /- as the mountpoint, and must contain only fully qualified paths as keys. For indirect maps, the final mount point is determined by concatenating the auto_master mountpoint with the map entry key and optional map entry mountpoint. For direct maps, the final mount point is determined by concatenating the map entry key with the optional map entry mountpoint.

The example above could be rewritten using direct map, by placing this in auto_master:

/- auto_example

and this in /etc/auto_example map file:

/example/x -intr,nfsv4

/example/share -fstype=smbfs,-N ://@server/share

/example/cd -fstype=cd9660 :/dev/cd0


Both auto_master and maps may contain entries consisting of a plus sign and map name:


Those entries cause automountd(8) daemon to retrieve the named map from directory services (like LDAP) and include it where the entry was.

If the file containing the map referenced in auto_master is not found, the map will be retrieved from directory services instead.

To retrieve entries from directory services, automountd(8) daemon runs /etc/autofs/include, which is usually a shell script, with map name as the only command line parameter. The script should output entries formatted according to auto_master or automounter map syntax to standard output. An example script to use LDAP is included in /etc/autofs/include_ldap. It can be symlinked to /etc/autofs/include.


  The default location of the auto_master file.
/etc/autofs/ Directory containing shell scripts to implement special maps and directory services.


autofs(5), automount(8), automountd(8), autounmountd(8)


The auto_master configuration file functionality was developed by
.An Edward Tomasz Napierala Aq Mt under sponsorship from the FreeBSD Foundation.
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