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

       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

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

                     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

                     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

         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 pairs.

       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 "unknown".

                     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 gethostname(2).

                     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 autofs.

                     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 autofs.

                     The string value of the key being looked up.

                     The string value of the map name used to lookup keys.

                     The string value of the full path to the mount being

                     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

                     Evaluates to false, the argument is ignored and may be

       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

                     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

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

                     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

                     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 lookup.

                     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

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 mount.

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),

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
       2020-11-01.  (At that time, the date of the most recent commit that
       was found in the repository was 2020-08-25.)  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)