AUTOMOUNT(1M) AUTOMOUNT(1M)
automount - automatically mount NFS filesystems
/usr/etc/automount [ -mnTv ] [ -D name=value ] [ -f master-file ] [ -p
priority ] [ -M mount-directory ] [ -tl duration ] [ -tm interval ] [ -tp
duration ] [ -tw interval ] [ directory mapname [ -mount-options ] ] ...
Automount is a daemon that automatically and transparently mounts NFS
filesystems as needed. Whenever a user on a client machine running
automount invokes a command that needs to access a remote file or
directory, the hierarchy to which that file or directory belongs is
mounted and remains mounted for as long as it is needed. When a certain
amount of time has elapsed during which the hierarchy is not accessed, it
is automatically unmounted. No mounting of unaccessed remote filesystems
is done at boot-time, and the user doesn't need special privilege to
mount a directory.
The automount daemon is started during system initialization from the
/etc/init.d/network script if the configuration flags ``nfs'' and
``automount'' are set ``on.'' Do the following commands as super-user to
enable automount:
/etc/chkconfig nfs on
/etc/chkconfig automount on
Rebooting will start automount with the options and arguments contained
in the file /etc/config/automount.options. The default version of this
file lets you access exported directories on another host with the
filename prefix of
/hosts/<hostname>/
For example, if host springfield exports /usr, then
ls /hosts/springfield/usr
will show the contents of that directory. You may want to customize this
file for your site.
Unlike mount, automount does not consult the file /etc/fstab for a list
of hierarchies to mount. Rather, it consults a series of maps, which can
be either direct or indirect. The names of the maps can be passed to
automount from the command line (via the /etc/config/automount.options
file), or from another (master) map.
The master map lists (as if from the command line) all other maps,
applicable options, and mount points.
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An indirect map allows you to specify mappings for the subdirectories you
wish to mount under the directory indicated on the command line. In an
indirect map, each directory field consists of the basename of a
subdirectory to be mounted as needed.
A direct map contains mappings for any number of directories. Each
directory listed in the map is automatically mounted as needed. The
direct map as a whole is not associated with any single directory.
automount appears to be an NFS server to the kernel. automount uses the
map contained in the mapname argument to locate an appropriate NFS file
server, exported filesystem, and mount options. It then mounts the
filesystem in a temporary location, and creates a symbolic link to the
temporary location. If the filesystem is not accessed within an
appropriate interval (five minutes by default), the daemon unmounts the
filesystem and removes the symbolic link. If the indicated directory has
not already been created, the daemon creates it, and then removes it upon
exiting.
By default, automount mounts everything under the directory /tmp_mnt.
For instance, if a user wants to mount a remote directory src under
/usr/src, the actual mount point will be /tmp_mnt/usr/src, and /usr/src
will be a symbolic link to that location.
As with any other kind of mount, a mount effected through the automounter
on a non-empty mount point will hide the original contents of the mount
point for as long as the mount is in effect.
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. Nor is there a need to maintain records of which hosts must be
mounted for what applications.
If the directory argument is a pathname, the map argument points to an
indirect map. An indirect map contains a list of the subdirectories
contained within the indicated directory. With an indirect map, it is
these subdirectories that are mounted automatically.
If the directory argument is `/-', automount treats the map argument that
follows as the name of a direct map. In a direct map, each entry
associates the full pathname of a mount point with a remote filesystem to
mount.
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, consists of the leading dash
and a comma-separated list of options to mount(1M), as described in
fstab(4). 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.
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-D var=value
Assign value to the indicated automount (environment) variable.
-f master-file
Read a local file for initialization, before reading the auto.master
NIS map. The information in master-file will take precedence.
-m Suppress initialization of directory-mapname pairs listed in the
auto.master NIS database.
-M mount-directory
Mount temporary filesystems in the named directory, instead of
/tmp_mnt.
-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 standard error.
-p priority
Set the (non-degrading) priority of the automount process. The
default is NDPNORMAX (40).
-tl duration
Specify a duration, in seconds, that a filesystem is to remain
mounted when not in use. The default is 300 seconds (5 minutes).
-tm interval
Specify an interval, in seconds, between attempts to mount a
filesystem. The default is 30 seconds.
-tp duration
Specify the duration, in seconds, that the results of a probe of a
server's availability will remain cached. The default is 5 seconds.
-tw interval
Specify an interval, in seconds, between attempts to unmount
filesystems that have exceeded their cached times. The default is
60 seconds.
-v Verbose. Log status and/or warning messages through syslog(3B) or
to the console.
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 environment of a user using
the automounter's services.
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If a variable 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:
directory [ -mount-options ] location ...
where directory is the full pathname of the directory to mount when used
in a direct map, or the basename of a subdirectory in an indirect map.
mount-options is a comma-separated list of options to mount(1M), as
described in fstab(4), and location specifies a remote filesystem from
which the directory may be mounted. In the simple case, location takes
the form:
hostname:pathname
Replicated Filesystems
Multiple location fields can be specified for replicated read-only
filesystems, in which case automount sends multiple mount requests;
automount mounts the filesystem from the first host that replies to the
mount request. This request is first made to the local net or subnet.
If there is no response, any connected server may respond. Since
automount does not monitor the status of the server while the filesystem
is mounted, it will not use another location in the list if the currently
mounted server crashes. This support for replicated filesystems is
available only at mount time. Once unmounted, another location may be
used for subsequent mounts of the filesystem.
If each location in the list shares the same pathname then a single
location may be used with a comma-separated list of hostnames:
hostname1,hostname2:pathname
Sharing Mounts
If location is specified in the form:
hostname:pathname:subdir
hostname is the name of the server from which to mount the filesystem,
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 filesystem may be accessed. With an
indirect map for /home such as:
bart springfield:/home/simpsons:bart
maggie springfield:/home/simpsons:maggie
and a user attempting to access a file in /home/bart, automount mounts
springfield:/home/simpsons, but creates a symbolic link called /home/bart
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to the bart subdirectory in the temporarily-mounted filesystem. If a
user immediately tries to access a file in /home/maggie, automount needs
only to create a symbolic link that points to the maggie subdirectory;
/home/simpsons is already mounted.
With the following map:
bart springfield:/home/simpsons/bart
maggie springfield:/home/simpsons/maggie
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
NEWLINE.
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 dollars
($) should be protected.
Directory Pattern Matching
The `&' character is expanded to the value of the directory field for the
entry in which it occurs. In this case:
bart springfield:/home/simpsons:&
the & expands to bart. The `*' character, when supplied as the directory
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:
* &:/home/&
this would allow automatic mounts in /home of any remote filesystem whose
location could be specified as:
hostname:/home/hostname
Multiple Mounts
A multiple mount entry takes the form:
directory [ /[ subdirectory [ -mount-options ] location ... ] ...
The initial / preceding the subdirectory is required; the optional
subdirectory is taken as a pathname relative to the directory. If
subdirectory is omitted in the first occurrence, the / refers to the
directory itself.
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Given the direct map entry:
/tools \
/ -ro dill:/tools mint:/tools \
/1.0 -ro mint:/tools/1.0 dill:/tools/1.0 \
/1.0/man -ro dill:/tools/1.0/man mint:/tools/1.0/man
automount would automatically mount /tools, /tools/1.0 and
/tools/1.0/man, as needed, from either dill or mint, 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.
Included Maps [Toc] [Back]
The contents of another map can be included within a map with an entry of
the form:
+mapname
mapname can either be a filename, or the name of an NIS map, or one of
the special maps described below. If the directory being searched for is
not located in an included map, the search continues with the next entry.
Special Maps [Toc] [Back]
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
filesystems from any host. For instance, if the following automount
command is already in effect:
automount /hosts -hosts
then a reference to /hosts/springfield/usr would initiate an automatic
mount of all filesystems from springfield that automount can mount;
references to a directory under /hosts/springfield will refer to the
corresponding directory relative to springfield's root.
The -null map, when indicated on the command line, cancels any subsequent
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 direct map.
Configuration and the auto.master Map [Toc] [Back]
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 duplications,
the command-line arguments take precedence over a local -f master map and
they both take precedence over an NIS auto.master map. This
configuration database contains arguments to the automount command,
rather than mappings; unless -f is in effect, automount does not look for
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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:
/homes auto.home
automount would mount home directories under /homes instead of /home, in
addition to the various directories specified in the /etc/auto.direct
file.
/tmp_mnt
directory under which filesystems are dynamically mounted
/etc/config/automount.options
site-dependent options and arguments
mount(1M), network(1M), chkconfig(1M), fstab(4), exports(4), schedctl(2)
The -hosts map mounts all of the exported filesystems, for which the
client has access, from a server. Use of the nohide export option on the
server (see exports(4)) may be used to minimize the number of mounts
performed by clients. Automount will not request a separate mount for a
nohide filesystem, if the client has access via the parent filesystem.
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 filesystems. If
a filesystem mounted with automount is unmounted with the umount(1M)
command, automount should be forced to reread the file by using the
command
/etc/killall -HUP automount
An ls(1) 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(2) 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 created within an
automounted filesystem.
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The recommended way to terminate automount services is to send a SIGTERM
signal to the daemon:
/etc/killall -TERM automount
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. automount must not be terminated with the SIGKILL
signal. Without an opportunity to unmount itself, the automount mount
points will appear to the kernel to belong to a non-responding NFS
server.
Since each direct map entry results in a separate mount for the mount
daemon, such maps should be kept short. Although both direct and
indirect maps can be modified at any time, entries added to a direct map
will have no effect until the automounter is restarted.
Automount mount points are mounted with type ignore; they do not appear
in the output of either mount(1M) or df(1). Automatically-mounted
filesystems, on the other hand, are mounted with type nfs and are
reported along with other NFS-mounted filesystems.
Shell filename expansion does not apply to objects not currently mounted.
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.
PPPPaaaaggggeeee 8888 [ Back ]
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