AUTOMOUNT(8) System Manager's Manual AUTOMOUNT(8)
automount - automatically mount NFS file systems
automount [ -mnTv ] [ -D name= value ] [ -f master-file ]
[ -M mount-directory ] [ -tl duration ]
[ -tm interval ] [ -tw interval ]
[ directory map [ -mount-options ] ] ...
automount is a daemon that automatically and transparently mounts an
NFS file system as needed. It monitors attempts to access directories
that are associated with an automount map, along with any directories
or files that reside under them. When a file is to be accessed, the
daemon mounts the appropriate NFS file system. You can assign a map to
a directory using an entry in a direct automount map, or by specifying
an indirect map on the command line.
The automount daemon appears to be an NFS server to the kernel. auto-
mount uses the map to locate an appropriate NFS file server, exported
file system, and mount options. It then mounts the file system in a
temporary location, and creates a symbolic link to the temporary loca-
tion. If the file system is not accessed within an appropriate inter-
val (five minutes by default), the daemon unmounts the file system and
removes the symbolic link. If the indicated directory has not already
been created, the daemon creates it, and then removes it upon exiting.
Since the name-to-location binding is dynamic, updates to an automount
map are transparent to the user. This obviates the need to ``pre-
mount'' shared file systems for applications that have ``hard coded''
references to files.
If the directory argument is a pathname, the map argument must be an
indirect map. In an indirect map the key for each entry is a simple
name that represents a symbolic link within directory to an NFS mount
If the directory argument is `/-', the map that follows must be a
direct map. A direct map is not associated with a single directory.
Instead, the key for each entry is a full pathname that will itself
appear to be a symbolic link to an NFS mount point.
A map can be a file or a Network Information Service (NIS) map; if a
file, the map argument must be a full pathname.
The -mount-options argument, when supplied, is a comma-separated list
of mount(8) options, preceded by a `-'. If these options are supplied,
they become the default mount options for all entries in the map.
Mount options provided within a map entry override these defaults.
-m Suppress initialization of directory-map pairs listed in the
auto.master NIS database.
-n Disable dynamic mounts. With this option, references through
the automount daemon only succeed when the target filesystem has
been previously mounted. This can be used to prevent NFS
servers from cross-mounting each other.
-T Trace. Expand each NFS call and display it on the standard out-
-v Verbose. Log status and/or warning messages to the console.
Assign value to the indicated automount (environment) variable.
Read a local file for initialization, ahead of the auto.master
Mount temporary file systems in the named directory, instead of
Specify a duration, in seconds, that a file system is to remain
mounted when not in use. The default is 5 minutes.
Specify an interval, in seconds, between attempts to mount a
filesystem. The default is 30 seconds.
Specify an interval, in seconds, between attempts to unmount
filesystems that have exceeded their cached times. The default
is 1 minute.
Environment variables can be used within an automount map. For
instance, if $HOME appeared within a map, automount would expand it to
its current value for the HOME variable. Environment variables are
expanded only for the automounter's environment -- not for the environ-
ment of a user using the automounter's services.
The special reference to $ARCH expands to the output of arch (1). This
can be useful in creating a map entry for mounting executables using a
server's export pathname that varies according to the architecture of
the client reading the map.
If a reference needs to be protected from affixed characters, you can
surround the variable name with curly braces.
Map Entry Format
A simple map entry (mapping) takes the form:
key [ -mount-options ] location ...
where key is the full pathname of the directory to mount when used in a
direct map, or simple name in an indirect map. mount-options is a
comma-separated list of mount options, and location specifies a remote
filesystem from which the directory may be mounted. In the simple
case, location takes the form:
Multiple location fields can be specified for replicated read-only
filesystems, in which case automount sends multiple mount requests;
automount mounts the file system from the first host that replies to
the mount request. This request is first made to the local net or sub-
net. If there is no response, any connected server may respond. Since
automount does not monitor the status of the server while the filesys-
tem is mounted it will not use another location in the list if the cur-
rently mounted server crashes. This support for replicated filesystems
is available only at mount time.
If each location in the list shares the same pathname then a single
location may be used with a comma-separated list of hostnames.
If location is specified in the form:
hostname is the name of the server from which to mount the file system,
pathname is the pathname of the directory to mount, and subdir, when
supplied, is the name of a subdirectory to which the symbolic link is
made. This can be used to prevent duplicate mounts when multiple
directories in the same remote file system may be accessed. With a map
for /home such as:
and a user attempting to access a file in /home/able, automount mounts
homeboy:/home/homeboy, but creates a symbolic link called /home/able to
the able subdirectory in the temporarily-mounted filesystem. If a user
immediately tries to access a file in /home/baker, automount needs only
to create a symbolic link that points to the baker subdirectory;
/home/homeboy is already mounted.
With the following map:
automount would have to mount the filesystem twice.
Comments and Quoting
A mapping can be continued across input lines by escaping the NEWLINE
with a backslash. Comments begin with a # and end at the subsequent
Characters that have special significance to the automount map parser
may be protected either with double quotes (") or by escaping with a
backslash (\). Pathnames with embedded whitespace, colons (:) or dol-
lar ($) should be protected.
Directory Pattern Matching
The `&&' character is expanded to the value of the key field for the
entry in which it occurs. In this case:
the && expands to able.
The `*' character, when supplied as the key field, is recognized as the
catch-all entry. Such an entry will be used if any previous entry has
not successfully matched the key being searched for. For instance, if
the following entry appeared in the indirect map for /home:
this would allow automatic mounts in /home of any remote file system
whose location could be specified as:
A multiple mount entry takes the form:
key [ /[mountpoint [ -mount-options ] location ... ] ...
The initial / within the `/[mountpoint]' is required; the optional
mountpoint is taken as a pathname relative to the destination of the
symbolic link for key. If mountpoint is omitted in the first occur-
rence, a mountpoint of / is implied.
Given the direct map entry:
/ -ro,intr arch:/arch/src alt:/arch/src \
/1.0 -ro,intr alt:/arch/src/1.0 arch:/arch/src/1.0 \
/1.0/man -ro,intr arch:/arch/src/1.0/man alt:/arch/src/1.0/man
automount would automatically mount /arch/src, /arch/src/1.0 and
/arch/src/1.0/man, as needed, from either arch or alt, whichever host
responded first. If the mounts are hierarchically related mounts
closer to the root must appear before submounts. All the mounts of a
multiple mount entry will occur together and will be unmounted
together. This is important if the filesystems reference each other
with relative symbolic links. Multiple mount entries can be used both
in direct maps and in indirect maps.
The contents of another map can be included within a map with an entry
of the form:
mapname can either be a filename, or the name of an NIS map, or one of
the special maps described below. If the key being searched for is not
located in an included map, the search continues with the next entry.
There are two special maps currently available: -hosts, and -null. The
-hosts map uses the NIS hosts.byname map to locate a remote host when
the hostname is specified. This map specifies mounts of all exported
file systems from any host. For instance, if the following automount
command is already in effect:
automount /net -hosts
then a reference to /net/hermes/usr would initiate an automatic mount
of all file systems from hermes that automount can mount; references to
a directory under /net/hermes will refer to the corresponding directory
relative to hermes root.
The -null map, when indicated on the command line, cancels any subse-
quent map for the directory indicated. It can be used to cancel a map
given in auto.master or for a mount point specified as an entry in a
Configuration and the auto.master Map
automount normally consults the auto.master NIS configuration map for a
list of initial automount maps, and sets up automatic mounts for them
in addition to those given on the command line. If there are duplica-
tions, the command-line arguments take precedence over a local -f mas-
ter map and they both take precedence over an NIS auto.master map.
This configuration database contains arguments to the automount com-
mand, rather than mappings; unless -f is in effect, automount does not
look for an auto.master file on the local host.
Maps given on the command line, or those given in a local auto.master
file specified with -f override those in the NIS auto.master map. For
instance, given the command:
automount -f /etc/auto.master /home -null /- etc/auto.direct
and a file named /etc/auto.master that contains:
automount would ignore /home entry in /etc/auto.master.
/tmp_mnt directory under which filesystems are dynamically
df(1V), ls(1V), stat(2V), passwd(5), mount(8)
The -hosts map must mount all the exported filesystems from a server.
If frequent access to just a single filesystem is required it is more
efficient to access the filesystem with a map entry that is tailored to
mount just the filesystem of interest.
When it receives signal number 1, SIGHUP, automount rereads the
/etc/mtab file to update its internal record of currently-mounted file
systems. If a file system mounted with automount is unmounted by a
umount command, automount should be forced to reread the file.
An ls(1V) listing of the entries in the directory for an indirect map
shows only the symbolic links for currently mounted filesystems. This
restriction is intended to avoid unnecessary mounts as a side effect of
programs that read the directory and stat(2V) each of the names.
Mount points for a single automounter must not be hierarchically
related. automount will not allow an automount mount point to be cre-
ated within an automounted filesystem.
automount must not be terminated with the SIGKILL signal (kill -9).
Without an opportunity to unmount itself, the automount mount points
will appear to the kernel to belong to a non-responding NFS server.
The recommended way to terminate automount services is to send a
SIGTERM (kill -15) signal to the daemon. This allows the automounter
to catch the signal and unmount not only its daemon but also any mounts
in /tmp_mnt. Mounts in /tmp_mnt that are busy will not be unmounted.
Since each direct map entry results in a separate mount for the mount
daemon such maps should be kept short. Entries added to a direct map
will have no effect until the automounter is restarted.
Entries in both direct and indirect maps can be modified at any time.
The new information will be used when automount next uses the map entry
to do a mount. automount does not cache map entries.
The Network Information Service (NIS) was formerly known as Sun Yellow
Pages (YP). The functionality of the two remains the same; only the
name has changed.
The bg mount option is not recognized by the automounter.
Since automount is single-threaded, any request that is delayed by a
slow or non-responding NFS server will delay all subsequent automatic
mount requests until it completes.
Programs that read /etc/mtab and then touch files that reside under
automatic mount points will introduce further entries to the file.
Automatically-mounted file systems are mounted with type ignore; they
do not appear in the output of either mount(8), or df(1V).
20 January 1990 AUTOMOUNT(8)