autofs(5) — Linux manual page


AUTOFS(5)                  File Formats Manual                 AUTOFS(5)

NAME         top

       autofs - Format of the automounter maps

DESCRIPTION         top

       The automounter maps are FILE, NIS, NISPLUS or LDAP (including
       LDAP via SSS) referred to by the master map of the automounter
       (see auto.master(5)).  These maps describe how file systems below
       the mount point of the map (given in the master map) are to be
       mounted.  This page describes the sun map format; if another map
       format, other than amd , is specified (e.g. hesiod), this
       documentation does not apply.

       Indirect maps, except for the internal hosts map, can be changed
       on the fly and the automouter will recognize those changes on the
       next operation it performs on that map. Direct maps require a HUP
       signal be sent to the daemon to refresh their contents as does
       the master map.

SUN FORMAT         top

       This is a description of the text file format.  Other methods of
       specifying these files may exist.  All empty lines or lines
       beginning with # are ignored. The basic format of one line in
       such maps is:

       key [-options] location

              For indirect mounts this is the part of the path name
              between the mount point and the path into the filesystem
              when it is mounted. Usually you can think about the key as
              a sub-directory name below the autofs managed mount point.

              For direct mounts this is the full path of each mount
              point. This map is always associated with the /- mount
              point in the master map.

              Zero or more options may be given.  Options can also be
              given in the auto.master file in which case both values
              are cumulative (this is a difference from SunOS).  The
              options are a list of comma separated options as customary
              for the mount(8) command.

              There are several special options

                     is used to specify a filesystem type if the
                     filesystem is not of the default NFS type.  This
                     option is processed by the automounter and not by
                     the mount command.

                     is used to treat errors when mounting file systems
                     as fatal. This is important when multiple file
                     systems should be mounted (`multi-mounts'). If this
                     option is given, no file system is mounted at all
                     if at least one file system can't be mounted.

                     is used to make the weight the sole factor in
                     selecting a server when multiple servers are
                     present in a map entry.

                     can be used to negate the option if it is present
                     in the master map entry for the map but is not
                     wanted for the given mount.

              The location specifies from where the file system is to be
              mounted.  In the most cases this will be an NFS volume and
              the usual notation host:pathname is used to indicate the
              remote filesystem and path to be mounted.  If the
              filesystem to be mounted begins with a / (such as local
              /dev entries or smbfs shares) a : needs to be prefixed
              (e.g.  :/dev/sda1).

EXAMPLE         top

       Indirect map:

         kernel    -ro,soft  
         boot      -fstype=ext2        :/dev/hda1
         windoze   -fstype=smbfs       ://windoze/c
         removable -fstype=ext2        :/dev/hdd
         cd        -fstype=iso9660,ro  :/dev/hdc
         floppy    -fstype=auto        :/dev/fd0
         server    -rw,hard            / -ro \
                                       /usr \

       In the first line we have a NFS remote mount of the kernel
       directory on  This is mounted read-only.  The
       second line mounts an ext2 volume from a local ide drive.  The
       third makes a share exported from a Windows machine available for
       automounting.  The rest should be fairly self-explanatory. The
       last entry (the last three lines) is an example of a multi-map
       (see below).

       If you use the automounter for a filesystem without access
       permissions (like vfat), users usually can't write on such a
       filesystem because it is mounted as user root.  You can solve
       this problem by passing the option gid=<gid>, e.g. gid=floppy.
       The filesystem is then mounted as group floppy instead of root.
       Then you can add the users to this group, and they can write to
       the filesystem. Here's an example entry for an autofs map:

         floppy-vfat  -fstype=vfat,sync,gid=floppy,umask=002  :/dev/fd0

       Direct map:

         /nfs/apps/mozilla             bogus:/usr/local/moxill
         /nfs/data/budgets             tiger:/usr/local/budgets
         /tst/sbin                     bogus:/usr/sbin

FEATURES         top

   Map Key Substitution
       An & character in the location is expanded to the value of the
       key field that matched the line (which probably only makes sense
       together with a wildcard key).

   Wildcard Key
       A map key of * denotes a wild-card entry. This entry is consulted
       if the specified key does not exist in the map.  A typical wild-
       card entry looks like this:

         *         server:/export/home/&

       The special character '&' will be replaced by the provided key.
       So, in the example above, a lookup for the key 'foo' would yield
       a mount of server:/export/home/foo.

   Variable Substitution
       The following special variables will be substituted in the
       location field of an automounter map entry if prefixed with $ as
       customary from shell scripts (curly braces can be used to
       separate the field name):

         ARCH           Architecture (uname -m)
         CPU            Processor Type
         HOST           Hostname (uname -n)
         OSNAME         Operating System (uname -s)
         OSREL          Release of OS (uname -r)
         OSVERS         Version of OS (uname -v)

       autofs provides additional variables that are set based on the
       user requesting the mount:

         USER           The user login name
         UID            The user login ID
         GROUP          The user group name
         GID            The user group ID
         HOME           The user home directory
         SHOST          Short hostname (domain part removed if present)

       If a program map is used these standard environment variables
       will have a prefix of "AUTOFS_" to prevent interpreted languages
       like python from being able to load and execute arbitrary code
       from a user home directory.

       Additional entries can be defined with the -Dvariable=Value map-
       option to automount(8).

   Executable Maps
       A map can be marked as executable. A program map will be called
       with the key as an argument.  It may return no lines of output if
       there's an error, or one or more lines containing a map entry
       (with \ quoting line breaks). The map entry corresponds to what
       would normally follow a map key.

       An executable map can return an error code to indicate the
       failure in addition to no output at all.  All output sent to
       stderr is logged into the system logs.

   Multiple Mounts
       A multi-mount map can be used to name multiple filesystems to
       mount.  It takes the form:

         key [ -options ] [[/] location [/relative-mount-point [ -options ] location...]...

       This may extend over multiple lines, quoting the line-breaks with
       `\´.  If present, the per-mountpoint mount-options are appended
       to the default mount-options. This behaviour may be overridden by
       the append_options configuration setting.

   Replicated Server
       A mount location can specify multiple hosts for a location,
       portentially with a different export path for the same file
       system. Historically these different locations are read-only and
       provide the same replicated file system.

         Multiple replicated hosts, same path:
         <path> host1,host2,hostn:/path/path

         Multiple hosts, some with same path, some with another
         <path> host1,host2:/blah host3:/some/other/path

         Multiple replicated hosts, different (potentially) paths:
         <path> host1:/path/pathA host2:/path/pathB

         Mutliple weighted, replicated hosts same path:
         <path> host1(5),host2(6),host3(1):/path/path

         Multiple weighted, replicated hosts different (potentially) paths:
         <path> host1(3):/path/pathA host2(5):/path/pathB

         Anything else is questionable and unsupported, but these variations will also work:
         <path> host1(3),host:/blah

UNSUPPORTED         top

       This version of the automounter supports direct maps stored in
       FILE, NIS, NISPLUS and LDAP (including LDAP via SSS) only.

AMD FORMAT         top

       This is a description of the text file format. Other methods of
       specifying mount map entries may be required for different map
       sources.  All empty lines or lines beginning with # are ignored.
       The basic format of one line in such maps is:

       key location-list

              A key is a path (or a single path component alone) that
              may end in the wildcard key, "*", or the wildcard key
              alone and must not begin with the "/" character.

              Following the key is a mount location-list.

       A location-list list has the following syntax:

       location[ location[ ... ]] [|| location[ location[ ... ]]

       A mount location-list can use the cut operator, ||, to specify
       locations that should be tried if none of the locations to the
       left of it where selected for a mount attempt.

       A mount location consists of an optional colon separated list of
       selectors, followed by a colon separated list of option:=value

       The selectors that may be used return a value or boolean result.
       Those that return a value may be to used with the comparison
       operators == and != and those that return a boolean result may be
       negated with the !.

       For a location to be selected for a mount attempt all of its
       selectors must evaluate to true. If a location is selected for a
       mount attempt and succeeds the lookup is completed and returns
       success. If the mount attempt fails the procedure continues with
       the next location until they have all been tried.

       In addition, some selectors take no arguments, some one argument
       and others optionally take two arguments.

       The selectors that take no arguments are:

                     The machine architecture which, if not set in the
                     configuration, is obtained using uname(2).

                     The machine kernel architecture which, if not set
                     in the configuration, is obtained using uname(2).

                     The operating system name, if not set in the
                     configuration, is obtained using uname(2).

                     The operating system version, if not set in the
                     configuration, is obtained using uname(2).

                     The full operating system name, if not set in the
                     configuration this selector has no value.

                     The operating system vendor name, if not set in the
                     configuration this selector has the value

                     The endianness of the hardware.

                     The name of the local cluster. It has a value only
                     if it is set in the configuration.

                     The base path under which external mounts are done
                     if they are needed.  Most mounts are done in place
                     but some can't be and this is the base path under
                     which those mounts will be done.

                     The local domain name. It is set to the value of
                     the configuration option sub_domain. If sub_domain
                     is not given in the configuration it is set to the
                     domain part of the local host name, as given by

                     The local host name, without the domain part, as
                     given by gethostname(2).

                     The full host name. If sub_domain is given in the
                     configuration this is set to the contatenation of
                     host and sub_domain deperated by a .. If sub_domain
                     is not set in the configuration the value of domain
                     is used instead of sub_domain.

                     The numeric value of the uid of the user that first
                     requested the mount. Note this is usual the same as
                     that used by amd but can be different within

                     The numeric value of the gid of the user that first
                     requested the mount. Note this is usual the same as
                     that used by amd but can be different within

                     The string value of the key being looked up.

                     The string value of the map name used to lookup

                     The string value of the full path to the mount
                     being requested.

                     Evaluates to the string "$".

       The selectors that take one argument are:

              in_network(network) ,  network(network) ,
              netnumber(network) ,  wire(network)
                     These selectors are all the same. in_network() is
                     the preferred usage. The network argument is an
                     address (which may include a subnet mask) or
                     network name. The function compares network against
                     each interface and returns true if network belongs
                     to the network the interface is connected to.

                     The xhost() selector compares hostname to the
                     ${host} and if it doesn't match it attempts to
                     lookup the cannonical name of hostname and compares
                     it to {host} as well.

                     Returns true if filename exits as determined by

                     Evaluates to true, the argument is ignored and may
                     be empty.

                     Evaluates to false, the argument is ignored and may
                     be empty.

       The selectors that take up to two arguments are:

                     The netgrp() selector returns true if hostname is a
                     member of the netgroup netgroup. If hostname is not
                     given ${host} is used for the comparison.

                     The netgrpd()i selector behaves the same as
                     netgrp() except that if hostname is not given
                     ${hostd}, the fully qualified hostname, is used
                     instead of ${host}.

       The options that may be used are:

                     This is the mount filesystem type.  It can have a
                     value of auto, link, linkx, host, lofs, ext2-4,
                     xfs, nfs, nfsl or cdfs.  Other types that are not
                     yet implemented or are not available in autofs are
                     nfsx, lustre, jfs, program, cachefs and direct.

                     The maptype option specifies the type of the map
                     source and can have a value of file, nis, nisplus,
                     exec, ldap or hesiod. Map sources either not yet
                     implemented or not available in autofs are sss,
                     ndbm, passwd and union.

                     The option fs is used to specify the local
                     filesystem. The meaning of this option (and whether
                     or not it is used) is dependent on the mount
                     filesystem type.

                     The remote host name for network mount requests.

                     The remote host filesystem path for network mount

                     Must resolve to the device file for local device
                     mount requests.

                     The sublink option is used to specify a
                     subdirectory within the mount location to which
                     this entry will point.

                     The pref option is used to specify a prefix that is
                     prepended to the lookup key before looking up the
                     map entry key.

                     The opts option is used to specify mount options to
                     be used for the mount. If a "-" is given it is
                     ignored.  Options that may be used are dependend on
                     the mount filesystem.

                     The addopts option is used to specify additional
                     mount options used in addition to the default mount
                     options for the mount location.

                     The addopts option is used to specify mount options
                     used instead the options given in opts when the
                     mount location is on a remote retwork.

       A number of options aren't available or aren't yet implemented
              within autofs, these are:

                     The cache option isn't used by autofs. The map
                     entry cache is continually updated and stale
                     entries cleaned on re-load when map changes are
                     detected so these configuration entries are not
                     used.  The regex map key matching is not
                     implemented and may not be due to the potential
                     overhead of the full map scans needed on every key

                     The cachefs filesystem is not available on Linux, a
                     different implementation is used for caching
                     network mounted file systems.

              mount ,  unmount ,  umount
                     These options are used by the amd program mount
                     type which is not yet implemented.

                     This option is not used by the autofs
                     implementation and is ignored.

FEATURES         top

   Key Matching
       The amd parser key matching is unusual.

       The key string to be looked up is constructed by prepending the
       prefix, if there is one.

       The resulting relative path string is matched by first trying the
       sting itself. If no match is found the last component of the key
       string is replaced with the wilcard match cahracter ("*") and a
       wildcard match is attemted. This process continues until a match
       is found or until the last match, against the wilcard match key
       alone, fails to match a map entry and the key lookup fails.

   Macro Usage
       Macros are used a lot in the autofs amd implementation.

       Many of the option values are set as macro variables
       corresponding to the option name during the map entry parse. So
       they may be used in subsequent option values. Beware though, the
       order in which option values is not necessarily left to right so
       you may get unexpected results.

EXAMPLE         top

       Example NFS mount map:

       Assuming we have the autofs master map entry:

         /test     file,amd:/etc/amd.test

       And the following map in /etc/amd.test:

         /defaults type:=nfs;rhost:=bilbo
         apps      rfs:=/autofs
         util      rhost:=zeus;rfs:=/work/util
         local     rfs:=/shared;sublink:=local

       In the first line we have an NFS remote mount of the exported
       directory /autofs from host bilbo which would be mounted on
       /test/apps. Next another nfs mount for the exported directory
       /work/util from host zeus.  This would be mounted on /test/util.

       Finally, we have an example of the use of the sublink option. In
       this case the filesystem bilbo:/shared would be mounted on a path
       external the automount directory (under the direcory given by
       configuration option auto_dir) and the path /test/local either
       symlinked or bind mounted (depending on the setting
       autofs_use_lofs) to the "local" subdirectory of the external

NOTES         top

       To be able to use IPv6 within autofs maps the package must be
       build to use the libtirpc library for its RPC communications.
       This is becuase the glibc RPC implementation doesn't support IPv6
       and is depricated so this is not likely to change.

SEE ALSO         top

       automount(8), auto.master(5), autofs(8), autofs.conf(5),
       mount(8), autofs_ldap_auth.conf(5).

AUTHOR         top

       This manual page was written by Christoph Lameter
       <>, for the Debian GNU/Linux system.  Edited by
       H. Peter Avian <>, Jeremy Fitzhardinge
       <> and Ian Kent <>.

COLOPHON         top

       This page is part of the autofs (automount) project.  Information
       about the project can be found at ⟨⟩.  If
       you have a bug report for this manual page, send it to  This page was obtained from the
       project's upstream Git repository
       ⟨git://⟩ on
       2024-06-14.  (At that time, the date of the most recent commit
       that was found in the repository was 2024-05-23.)  If you
       discover any rendering problems in this HTML version of the page,
       or you believe there is a better or more up-to-date source for
       the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original
       manual page), send a mail to

                               9 Feb 2014                      AUTOFS(5)

Pages that refer to this page: auto.master(5)autofs(8)automount(8)