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AUTO.MASTER(5) File Formats Manual AUTO.MASTER(5)


auto.master - Master Map for automounter consulted by autofs


The auto.master map is consulted to set up automount managed mount points when the autofs(8) script is invoked or the automount(8) program is run. Each line describes a mount point and refers to an autofs map describing file systems to be mounted under the mount point.

The default location of the master map is /etc/auto.master but an alternate name may be given on the command line when running the automounter and the default master map may changed by setting the MASTER_MAP_NAME configuration variable in /etc/default/autofs. If the master map name has no path then the system Name Service Switch configuration will be consulted and each of the sources searched in line with the rules given in the Name Service Switch configuration.

Access to mounts in maps is governed by a key.

For direct maps the mount point is always specified as:


and the key used within the direct map is the full path to the mount point. The direct map may have multiple entries in the master map.

For indirect maps access is by using the path scheme:


where mount-point is one of the entries listed in the master map. The key is a single directory component and is matched against entries in the map given in the entry (See autofs(5)).

Additionally, a map may be included from its source as if it were itself present in the master map by including a line of the form:

+[maptype[,format]:]map [options]

and automount(8) will process the map according to the specification described below for map entries. Plus map inclusion is only permitted in file map sources. Indirect map entries must be unique in the master map so second and subsequent entries for an indirect mount point are ignored by automount(8).

autofs currently does not collapse multiple slashes in paths, so it is important to ensure paths used in maps are correct. If unnecessary multiple slashes are present in a path it can lead to unexpected failures such as an inability to expire automounts. An exception to this is a trailing slash at the end of the automount point path in the master map which will be removed if present.


Master map entries have three fields separated by an arbitrary number of spaces or tabs. Lines beginning with # are comments. The first field is the mount point described above and the second field is the name of the map to be consulted for the mount point followed by the third field which contains options to be applied to all entries in the map.

The format of a master map entry is:

mount-point [map-type[,format]:]map [options]
Base location for the autofs filesystem to be mounted. For indirect maps this directory will be created (as with mkdir -p) and is removed when the autofs filesystem is umounted.
Type of map used for this mount point. The following are valid map types:
The map is a regular text file.
The map is an executable program, which is passed a key on the command line and returns an entry (everything besides the key) on stdout if successful. Optionally, the keyword exec may be used as a synonym for program to avoid confusion with amd formatted maps mount type program.
The map is a NIS (YP) database.
The map is a NIS+ database.
The map is a hesiod database whose filsys entries are used for maps.
The map is stored in an LDAP directory. If ldaps is used the appropriate certificate must be configured in the LDAP client.
This map type allows the specification of multiple maps separated by "--". These maps are searched in order to resolve key lookups.
This map type can be used at + master map including notation. The contents of files under given directory are included to the master map. The name of file to be included must be ended with ".autofs". A file will be ignored if its name is not ended with the suffix. In addition a dot file, a file which name is started with "." is also ignored.

Format of the map data; currently the formats recognized are sun, which is a subset of the Sun automounter map format, hesiod, for hesiod filesys entries and amd for amd formatted map entries. If the format is left unspecified, it defaults to sun for all map types except hesiod unless it is a top level amd mount that has a configuration entry for the mount point path, in which case the format used is amd.

Name of the map to use. This is an absolute UNIX pathname for maps of types file, dir, or program, and the name of a database in the case for maps of type yp, nisplus, or hesiod or the dn of an LDAP entry for maps of type ldap.

Any remaining command line arguments without leading dashes (-) are taken as options (-o) to mount. Arguments with leading dashes are considered options for the maps and are passed to automount (8).

The sun format supports the following options:

Replace variable with value in map substitutions.
Treat errors when mounting file systems as fatal. This is important when multiple file systems should be mounted (`multimounts'). If this option is given, no file system is mounted at all if at least one file system can't be mounted.
This is an autofs specific option that is a pseudo mount option and so is given without a leading dash. Use of the browse option pre-creates mount point directories for indirect mount maps so the map keys can be seen in a directory listing without being mounted. Use of this option can cause performance problem if the indirect map is large so it should be used with caution. The internal program default is to enable browse mode for indirect mounts but the default installed configuration overrides this by setting BROWSE_MODE to "no" because of the potential performance problem. This option does the same as the deprecated --ghost option, the browse option is preferred because it is used by other autofs implementations.
This is an autofs specific option that is a pseudo mount option and so is given without a leading dash. It may be used either in the master map entry (so it effects all the map entries) or with individual map entries to prevent bind mounting of local NFS filesystems. For direct mount maps the option is only effective if specified on the first direct map entry and is applied to all direct mount maps in the master map. It is ignored if given on subsequent direct map entries. It may be used on individual map entries of both types. Preventing bind mounts of NFS file systems can no longer be done by using the "port=" option, the nobind option must be used instead.
This option makes bind mounting use a symlink instead of an actual bind mount. It is an autofs specific option that is a pseudo mount option and so is given without a leading dash. It may be used with indirect map entries only, either in the master map (so it effects all map entries) or with individual map entries. The option is ignored for direct mounts and non-root offest mount entries.
Use a strict expire policy for this automount. Using this option means that last use of autofs directory entries will not be updated during path walks so that mounts in an automount won't be kept mounted by applications scanning the mount tree. Note that this doesn't completely resolve the problem of expired automounts being immediately re-mounted due to application accesses triggered by the expire itself.
This option allows mount propagation of bind mounts to be set to slave, private or shared. This option defaults to slave if no option is given. When using multi-mounts that have bind mounts the bind mount will have the same properties as its parent which is commonly propagation shared. And if the mount target is also propagation shared this can lead to a deadlock when attempting to access the offset mounts. When this happens an unwanted offset mount is propagated back to the target file system resulting in a deadlock since the automount target is itself an (unwanted) automount trigger. This option is an autofs pseudo mount option that can be used in the master map only.
Enables the use of random selection when choosing a host from a list of replicated servers. This option is applied to this mount only, overriding the global setting that may be specified on the command line.
Use only specified weights for server selection where more than one server is specified in the map entry. If no server weights are given then each available server will be tried in the order listed, within proximity.
Set the expire timeout for map entries. This option can be used to override the global default given either on the command line or in the configuration.
Set the timeout for caching failed key lookups. This option can be used to override the global default given either on the command line or in the configuration.
Set the directory mode for the base location of the autofs mount point. If this option is given, autofs will chmod that directory with this mode.


If "-hosts" is given as the map then accessing a key under the mount point which corresponds to a hostname will allow access to the exports of that host. The hosts map cannot be dynamically updated and requires a HUP signal to be sent to the daemon for it to check hosts for an update. Due to possible hierarchic dependencies within a mount tree, it might not be completely updated during the HUP signal processing.

For example, with an entry in the master map of /net -hosts accessing /net/myserver will mount exports from myserver on directories below /net/myserver.

NOTE: mounts done from a hosts map will be mounted with the "nosuid,nodev" options unless overridden by explicitly specifying the "suid", "dev" options in the master map entry.


If "-null" is given as the map it is used to tell automount(8) to ignore a subsequent master map entry with the given path.

It can be used for paths that appear in the master map or in direct mount maps (but not in direct mount maps themselves) or as a key in an indirect mount map.

An indirect mount map key can be nulled. If so the map key is ignored and does not result in a mount attempt (essentially the key lookup is abandoned early on).

An indirect mount map top level mount point path can be nulled. If so no mounts from the nulled mount are performed (essentially it isn't mounted).

Direct mount map path entries can be nulled. Since they must be present at startup they are (notionally) part of the master map so direct mount paths that use the -null map may be used in the master map to ignore subsequent direct mount map entries.

A nulled master map entry path will ignore a single subsequent matching entry. Any matching entry following that will be treated as it normally would be. An example use of this is allowing local master map entries to override remote ones.

NOTE: If a duplicate master map entry path is seen (excluding paths of null entries) it will be ignored and noted in the log, that is the first encountered master map entry is used unless there is a corresponding null entry.


If the map type ldap is specified the mapname is of the form [//servername/]dn, where the optional servername is the name of the LDAP server to query, and dn is the Distinguished Name of a subtree to search for map entries. The old style ldap:servername:mapname is also understood. Alternatively, the type can be obtained from the Name Service Switch configuration, in which case the map name alone must be given.

If no schema is set in the autofs configuration then autofs will check each of the commonly used schema for a valid entry and if one is found it will be used for subsequent lookups.

There are three common schemas in use:

Entries in the nisMap schema are nisObject objects in the specified subtree, where the cn attribute is the key (the wildcard key is "/"), and the nisMapEntry attribute contains the information used by the automounter.
The automountMap schema has two variations that differ in the attribute used for the map key. Entries in the automountMap schema are automount objects in the specified subtree, where the cn or automountKey attribute (depending on local usage) is the key (the wildcard key is "/"), and the automountInformation attribute contains the information used by the automounter. Note that the cn attribute is case insensitive.

The object classes and attributes used for accessing automount maps in LDAP can be changed by setting entries in the autofs configuration located in /etc/default/autofs.conf.

If a schema is given in the configuration then all the schema configuration values must be set, any partial schema specification will be ignored.

The amdmap schema contains attributes amdmapName, amdmapKey and amdmapValue where amdmapName contains the name of the containing map, amdmapKey contains the map key and amdmapValue contains the map entry.


LDAP authenticated binds, TLS encrypted connections and certification may be used by setting appropriate values in the autofs authentication configuration file and configuring the LDAP client with appropriate settings. The default location of this file is /etc/autofs_ldap_auth.conf.

If this file exists it will be used to establish whether TLS or authentication should be used.

An example of this file is:

<?xml version="1.0" ?>

secret="abc" />

If TLS encryption is to be used the location of the Certificate Authority certificate must be set within the LDAP client configuration in order to validate the server certificate. If, in addition, a certified connection is to be used then the client certificate and private key file locations must also be configured within the LDAP client.

In OpenLDAP these may be configured in the ldap.conf file or in the per-user configuration. For example, it may be sensible to use the system wide configuration for the location of the Certificate Authority certificate and set the location of the client certificate and private key in the per-user configuration. The location of these files and the configuration entry requirements is system dependent so the documentation for your installation will need to be consulted to get further information.

See autofs_ldap_auth.conf (5) for more information.


/home	/etc/auto.home

This will generate two mountpoints for /home and /mnt and install direct mount triggers for each entry in the direct mount map All accesses to /home will lead to the consultation of the map in /etc/auto.home and all accesses to /mnt will consult the NIS map All accesses to paths in the map will trigger mounts when they are accessed and the Name Service Switch configuration will be used to locate the source of the map

To avoid making edits to /etc/auto.master, /etc/auto.master.d may be used. Files in that directory must have a ".autofs" suffix, e.g. /etc/auto.master.d/extra.autofs. Such files contain lines of the same format as the auto.master file, e.g.

/foo    /etc/


automount(8), autofs(5), autofs(8), autofs.conf(5), autofs_ldap_auth.conf(5).


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

11 Apr 2006