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NAME | DESCRIPTION | SUN FORMAT | EXAMPLE | FEATURES | UNSUPPORTED | AMD FORMAT | FEATURES | EXAMPLE | NOTES | SEE ALSO | AUTHOR | COLOPHON |
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AUTOFS(5) File Formats Manual AUTOFS(5)
autofs - Format of the automounter maps
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.
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
key
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.
options
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
-fstype=
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.
-strict
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.
-use-weight-only
is used to make the weight the sole factor in
selecting a server when multiple servers are present
in a map entry.
-no-use-weight-only
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.
location
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).
Indirect map:
kernel -ro,soft ftp.kernel.org:/pub/linux
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 myserver.me.org:/ \
/usr myserver.me.org:/usr \
/home myserver.me.org:/home
In the first line we have a NFS remote mount of the kernel
directory on ftp.kernel.org. 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
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
This version of the automounter supports direct maps stored in
FILE, NIS, NISPLUS and LDAP (including LDAP via SSS) only.
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
key
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.
location-list
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:
arch
The machine architecture which, if not set in the
configuration, is obtained using uname(2).
karch
The machine kernel architecture which, if not set in
the configuration, is obtained using uname(2).
os
The operating system name, if not set in the
configuration, is obtained using uname(2).
osver
The operating system version, if not set in the
configuration, is obtained using uname(2).
full_os
The full operating system name, if not set in the
configuration this selector has no value.
vendor
The operating system vendor name, if not set in the
configuration this selector has the value "unknown".
byte
The endianness of the hardware.
cluster
The name of the local cluster. It has a value only
if it is set in the configuration.
autodir
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.
domain
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).
host
The local host name, without the domain part, as
given by gethostname(2).
hostd
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.
uid
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.
gid
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.
key
The string value of the key being looked up.
map
The string value of the map name used to lookup
keys.
path
The string value of the full path to the mount being
requested.
dollar
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.
xhost(hostname)
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.
exists(filename)
Returns true if filename exits as determined by
lstat(2).
true()
Evaluates to true, the argument is ignored and may
be empty.
false()
Evaluates to false, the argument is ignored and may
be empty.
The selectors that take up to two arguments are:
netgrp(netgroup[,hostname])
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.
netgrpd(netgroup[,hostname])
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:
type
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.
maptype
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.
fs
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.
rhost
The remote host name for network mount requests.
rfs
The remote host filesystem path for network mount
requests.
dev
Must resolve to the device file for local device
mount requests.
sublink
The sublink option is used to specify a subdirectory
within the mount location to which this entry will
point.
pref
The pref option is used to specify a prefix that is
prepended to the lookup key before looking up the
map entry key.
opts
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.
addopts
The addopts option is used to specify additional
mount options used in addition to the default mount
options for the mount location.
remopts
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:
cache
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.
cachedir
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.
delay
This option is not used by the autofs implementation
and is ignored.
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 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.
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.
automount(8), auto.master(5), autofs(8), autofs.conf(5), mount(8),
autofs_ldap_auth.conf(5).
This manual page was written by Christoph Lameter
<chris@waterf.org>, for the Debian GNU/Linux system. Edited by H.
Peter Avian <hpa@transmeta.com>, Jeremy Fitzhardinge
<jeremy@goop.org> and Ian Kent <raven@themaw.net>.
This page is part of the autofs (automount) project. Information
about the project can be found at ⟨http://www.autofs.org/⟩. If
you have a bug report for this manual page, send it to
autofs@vger.kernel.org. This page was obtained from the project's
upstream Git repository
⟨git://git.kernel.org/pub/scm/linux/storage/autofs/autofs.git⟩ on
2025-08-11. (At that time, the date of the most recent commit
that was found in the repository was 2024-08-14.) 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 man-pages@man7.org
9 Feb 2014 AUTOFS(5)
Pages that refer to this page: auto.master(5), autofs(8), automount(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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