HardenedBSD/usr.sbin/autofs/auto_master.5

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.Dd December 27, 2023
.Dt AUTO_MASTER 5
.Os
.Sh NAME
.Nm auto_master
.Nd autofs automounter configuration and map file format
.Sh DESCRIPTION
The automounter configuration consists of the
.Nm
configuration file, which assigns filesystem paths to map names,
and maps, which contain actual mount information.
The
.Nm
configuration file is used by the
.Xr automount 8
command.
Map files are read by the
.Xr automountd 8
daemon.
.Sh AUTO_MASTER SYNTAX
The
.Nm
file consists of lines with two or three entries separated by whitespace
and terminated by newline character:
.Bd -literal -offset indent
.Pa mountpoint Pa map_name Op Ar -options
.Ed
.Pp
.Pa mountpoint
is either a fully specified path, or
.Li /- .
When
.Pa mountpoint
is a full path,
.Pa map_name
must reference an indirect map.
Otherwise,
.Pa map_name
must reference a direct map.
See
.Sx "MAP SYNTAX" below.
.Pp
.Pa map_name
specifies map to use.
If
.Pa map_name
begins with
.Li - ,
it specifies a special map.
See
.Sx "MAP SYNTAX"
below.
If
.Pa map_name
is not a fully specified path
.Pq it does not start with Li / ,
.Xr automountd 8
will search for that name in
.Li /etc .
Otherwise it will use the path as given.
If the file indicated by
.Pa map_name
is executable,
.Xr automountd 8
will assume it is an executable map.
See
.Sx "MAP SYNTAX"
below.
Otherwise, the file is opened and the contents parsed.
.Pp
.Pa -options
is an optional field that starts with
.Li -
and can contain generic filesystem mount options.
.Pp
The following example specifies that the /etc/auto_example indirect map
will be mounted on /example.
.Bd -literal -offset indent
/example auto_example
.Ed
.Sh MAP SYNTAX
Map files consist of lines with a number of entries separated by whitespace
and terminated by newline character:
.Bd -literal -offset indent
.Pa key Oo Ar -options Oc Oo Ar mountpoint Oo -options Oc Oc Ar location Op ...
.Ed
.Pp
In most cases, it can be simplified to:
.Bd -literal -offset indent
.Pa key Oo Ar -options Oc Ar location
.Ed
.Pp
.Pa key
is the path component used by
.Xr automountd 8
to find the right map entry to use.
It is also used to form the final mountpoint.
A wildcard
.Pq Ql *
can be used for the key.
It matches every directory that does not match other keys.
Those directories will not be visible to the user
until accessed.
.Pp
The
.Ar options
field, if present, must begin with
.Li - .
When mounting the filesystem, options supplied to
.Nm
and options specified in the map entry are concatenated together.
The special option
.Li fstype
is used to specify filesystem type.
It is not passed to the mount program as an option.
Instead, it is passed as an argument to
.Cm "mount -t".
The default
.Li fstype
is
.Ql nfs .
The special option
.Li nobrowse
is used to disable creation of top-level directories for special
and executable maps.
.Pp
The optional
.Pa mountpoint
field is used to specify multiple mount points
for a single key.
.Pp
The
.Ar location
field specifies the filesystem to be mounted.
Ampersands
.Pq Ql &
in the
.Ar location
field are replaced with the value of
.Ar key .
This is typically used with wildcards, like:
.Bd -literal -offset indent
.Li *	192.168.1.1:/share/&
.Ed
.Pp
The
.Ar location
field may contain references to variables, like:
.Bd -literal -offset indent
.Li sys	192.168.1.1:/sys/${OSNAME}
.Ed
.Pp
Defined variables are:
.Pp
.Bl -tag -width "-OSNAME" -compact
.It Li ARCH
Expands to the output of
.Li "uname -p" .
.It Li CPU
Same as ARCH.
.It Li DOLLAR
A literal $ sign.
.It Li HOST
Expands to the output of
.Li "uname -n" .
.It Li OSNAME
Expands to the output of
.Li "uname -s" .
.It Li OSREL
Expands to the output of
.Li "uname -r" .
.It Li OSVERS
Expands to the output of
.Li "uname -v" .
.El
.Pp
Additional variables can be defined with the
.Fl D
option of
.Xr automount 8
and
.Xr automountd 8 .
.Pp
To pass a location that begins with
.Li / ,
prefix it with a colon.
For example,
.Li :/dev/cd0 .
.Pp
This example, when put into
.Pa /etc/auto_example ,
and with
.Nm
referring to the map as described above, specifies that the NFS share
.Li 192.168.1.1:/share/example/x
will be mounted on
.Pa /example/x/
when any process attempts to access that mountpoint, with
.Li intr
and
.Li nfsv4
mount options, described in
.Xr mount_nfs 8 :
.Bd -literal -offset indent
.Li x -intr,nfsv4 192.168.1.1:/share/example/x
.Ed
.Pp
Automatically mount an SMB share on access, as a guest user,
without prompting for a password:
.Bd -literal -offset indent
.Li share -fstype=smbfs,-N ://@server/share
.Ed
.Pp
Automatically mount the CD drive on access:
.Bd -literal -offset indent
.Li cd -fstype=cd9660 :/dev/cd0
.Ed
.Sh SPECIAL MAPS
Special maps have names beginning with
.Li - .
Supported special maps are:
.Pp
.Bl -tag -width "-noauto" -compact
.It Li -hosts
Query the remote NFS server and map exported shares.
This map is traditionally mounted on
.Pa /net .
Access to files on a remote NFS server is provided through the
.Pf /net/ Ar nfs-server-ip Ns / Ns Ar share-name Ns /
directory without any additional configuration.
Directories for individual NFS servers are not present until the first access,
when they are automatically created.
.It Li -media
Query devices that are not yet mounted, but contain valid filesystems.
Generally used to access files on removable media.
.It Li -noauto
Mount filesystems configured in
.Xr fstab 5
as "noauto".
This needs to be set up as a direct map.
.It Li -null
Prevent
.Xr automountd 8
from mounting anything on the mountpoint.
.El
.Pp
It is possible to add custom special maps by adding them, as executable
maps named
.Pa special_foo ,
to the
.Pa /etc/autofs/
directory.
.Sh EXECUTABLE MAPS
If the map file specified in
.Nm
has the execute bit set,
.Xr automountd 8
will execute it and parse the standard output instead of parsing
the file contents.
When called without command line arguments, the executable is
expected to output a list of available map keys separated by
newline characters.
Otherwise, the executable will be called with a key name as
a command line argument.
Output from the executable is expected to be the entry for that key,
not including the key itself.
.Sh INDIRECT VERSUS DIRECT MAPS
Indirect maps are referred to in
.Nm
by entries with a fully qualified path as a mount point, and must contain only
relative paths as keys.
Direct maps are referred to in
.Nm
by entries with
.Li /-
as the mountpoint, and must contain only fully qualified paths as keys.
For indirect maps, the final mount point is determined by concatenating the
.Nm
mountpoint with the map entry key and optional map entry mountpoint.
For direct maps, the final mount point is determined by concatenating
the map entry key with the optional map entry mountpoint.
.Pp
The example above could be rewritten using direct map, by placing this in
.Nm :
.Bd -literal -offset indent
.Li /- auto_example
.Ed
.Pp
and this in
.Li /etc/auto_example
map file:
.Bd -literal -offset indent
.Li /example/x -intr,nfsv4 192.168.1.1:/share/example/x
.Li /example/share -fstype=smbfs,-N ://@server/share
.Li /example/cd -fstype=cd9660 :/dev/cd0
.Ed
.Sh DIRECTORY SERVICES
Both
.Nm
and maps may contain entries consisting of a plus sign and map name:
.Bd -literal -offset indent
.Li +auto_master
.Ed
.Pp
Those entries cause
.Xr automountd 8
daemon to retrieve the named map from directory services (like LDAP)
and include it where the entry was.
.Pp
If the file containing the map referenced in
.Nm
is not found, the map will be retrieved from directory services instead.
.Pp
To retrieve entries from directory services,
.Xr automountd 8
daemon runs
.Pa /etc/autofs/include ,
which is usually a shell script, with map name as the only command line
parameter.
The script should output entries formatted according to
.Nm
or automounter map syntax to standard output.
An example script to use LDAP is included in
.Pa /etc/autofs/include_ldap .
It can be symlinked to
.Pa /etc/autofs/include .
.Sh FILES
.Bl -tag -width ".Pa /etc/auto_master" -compact
.It Pa /etc/auto_master
The default location of the
.Pa auto_master
file.
.It Pa /etc/autofs/
Directory containing shell scripts to implement special maps and directory
services.
.El
.Sh SEE ALSO
.Xr autofs 4 ,
.Xr automount 8 ,
.Xr automountd 8 ,
.Xr autounmountd 8
.Sh AUTHORS
The
.Nm
configuration file functionality was developed by
.An Edward Tomasz Napierala Aq Mt trasz@FreeBSD.org
under sponsorship from the FreeBSD Foundation.