mount.8

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.\" Copyright (c) 1996 Andries Brouwer
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.\" (c) 1980, 1989, 1991 The Regents of the University of California
.\" and had been heavily modified by Rik Faith and myself.
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.\" 960705, aeb: version for mount-2.7g
.\" 970114, aeb: xiafs and ext are dead; romfs is new
.\" 970623, aeb: -F option
.\" 970914, reg: -s option
.\" 981111, K.Garloff: /etc/filesystems
.\" 990111, aeb: documented /sbin/mount.smbfs
.\" 990730, Yann Droneaud <[e-mail]>: updated page
.\" 991214, Elrond <[e-mail]>: added some docs on devpts
.\" 010714, Michael K. Johnson <[e-mail]> added -O
.\" 010725, Nikita Danilov <[e-mail]>: reiserfs options
.\" 011124, Karl Eichwalder <[e-mail]>: tmpfs options
.\"
.TH MOUNT 8 "14 September 1997" "Linux 2.0" "Linux Programmer's Manual"
.SH NAME
mount \- mount a file system
.SH SYNOPSIS
.BI "mount [\-lhV]"
.LP
.BI "mount \-a [\-fFnrsvw] [\-t " vfstype "] [\-O " optlist ]
.br
.BI "mount [\-fnrsvw] [\-o " options " [,...]] " "device " | " dir"
.br
.BI "mount [\-fnrsvw] [\-t " vfstype "] [\-o " options "] " "device dir"
.SH DESCRIPTION
All files accessible in a Unix system are arranged in one big
tree, the file hierarchy, rooted at
.BR / .
These files can be spread out over several devices. The
.B mount
command serves to attach the file system found on some device
to the big file tree. Conversely, the
.BR umount (8)
command will detach it again.

The standard form of the
.B mount
command, is
.RS
.br
.BI "mount \-t" " type device dir"
.RE
This tells the kernel to attach the file system found on
.I device
(which is of type
.IR type )
at the directory
.IR dir .
The previous contents (if any) and owner and mode of
.I dir
become invisible, and as long as this file system remains mounted,
the pathname
.I dir
refers to the root of the file system on
.IR device .

Three forms of invocation do not actually mount anything:
.RS
.br
.B "mount \-h"
.RE
prints a help message;
.RS
.br
.B "mount \-V"
.RE
prints a version string; and just
.RS
.BI "mount [-l] [-t" " type" ]
.RE
lists all mounted file systems (of type
.IR type ).
The option \-l adds the (ext2, ext3 and XFS) labels in this listing.
See below.

.\" In fact since 2.3.99. At first the syntax was mount -t bind.
Since Linux 2.4.0 it is possible to remount part of the
file hierarchy somewhere else. The call is
.RS
.br
.B "mount --bind olddir newdir"
.RE
After this call the same contents is accessible in two places.
One can also remount a single file (on a single file).

This call attaches only (part of) a single filesystem, not possible
submounts. The entire file hierarchy including submounts is attached
a second place using
.RS
.br
.B "mount --rbind olddir newdir"
.RE
.\" available since Linux 2.4.11.
The mount options are not changed.

Since Linux 2.5.1 it is possible to atomically move a mounted tree
to another place. The call is
.RS
.br
.B "mount --move olddir newdir"
.RE

The
.I proc
file system is not associated with a special device, and when
mounting it, an arbitrary keyword, such as
.I proc
can be used instead of a device specification.
(The customary choice
.I none
is less fortunate: the error message `none busy' from
.B umount
can be confusing.)

Most devices are indicated by a file name (of a block special device), like
.IR /dev/sda1 ,
but there are other possibilities. For example, in the case of an NFS mount,
.I device
may look like
.IR knuth.cwi.nl:/dir .
It is possible to indicate a block special device using its
volume label or UUID (see the \-L and \-U options below).

The file
.I /etc/fstab
(see
.BR fstab (5)),
may contain lines describing what devices are usually
mounted where, using which options. This file is used in three ways:
.LP
(i) The command
.RS
.br
.BI "mount \-a [\-t " type "] [\-O " optlist ]
.RE
(usually given in a bootscript) causes all file systems mentioned in
.I fstab
(of the proper type and/or having or not having the proper options)
to be mounted as indicated, except for those whose line contains the
.B noauto
keyword. Adding the
.B \-F
option will make mount fork, so that the
filesystems are mounted simultaneously.
.LP
(ii) When mounting a file system mentioned in
.IR fstab ,
it suffices to give only the device, or only the mount point.
.LP
(iii) Normally, only the superuser can mount file systems.
However, when
.I fstab
contains the
.B user
option on a line, then anybody can mount the corresponding system.
.LP
Thus, given a line
.RS
.br
.B "/dev/cdrom  /cd  iso9660  ro,user,noauto,unhide"
.RE
any user can mount the iso9660 file system found on his CDROM
using the command
.RS
.br
.B "mount /dev/cdrom"
.RE
or
.RS
.br
.B "mount /cd"
.RE
For more details, see
.BR fstab (5).
Only the user that mounted a filesystem can unmount it again.
If any user should be able to unmount, then use
.B users
instead of
.B user
in the
.I fstab
line.
The
.B owner
option is similar to the
.B user
option, with the restriction that the user must be the owner
of the special file. This may be useful e.g. for
.I /dev/fd
if a login script makes the console user owner of this device.
The
.B group
option is similar, with the restriction that the user must be
member of the group of the special file.

The programs
.B mount
and
.B umount
maintain a list of currently mounted file systems in the file
.IR /etc/mtab .
If no arguments are given to
.BR mount ,
this list is printed.

When the
.I proc
filesystem is mounted (say at
.IR /proc ),
the files
.I /etc/mtab
and
.I /proc/mounts
have very similar contents. The former has somewhat
more information, such as the mount options used,
but is not necessarily up-to-date (cf. the
.B \-n
option below). It is possible to replace
.I /etc/mtab
by a symbolic link to
.IR /proc/mounts ,
and especially when you have very large numbers of mounts
things will be much faster with that symlink,
but some information is lost that way, and in particular
working with the loop device will be less convenient,
and using the "user" option will fail.

.SH OPTIONS
The full set of options used by an invocation of
.B mount
is determined by first extracting the
options for the file system from the
.I fstab
table, then applying any options specified by the
.B \-o
argument, and finally applying a
.BR \-r " or " \-w
option, when present.

Options available for the
.B mount
command:
.TP
.B \-V
Output version.
.TP
.B \-h
Print a help message.
.TP
.B \-v
Verbose mode.
.TP
.B \-a
Mount all filesystems (of the given types) mentioned in
.IR fstab .
.TP
.B \-F
(Used in conjunction with
.BR \-a .)
Fork off a new incarnation of mount for each device.
This will do the mounts on different devices or different NFS servers
in parallel.
This has the advantage that it is faster; also NFS timeouts go in
parallel. A disadvantage is that the mounts are done in undefined order.
Thus, you cannot use this option if you want to mount both
.I /usr
and
.IR /usr/spool .
.TP
.B \-f
Causes everything to be done except for the actual system call; if it's not
obvious, this ``fakes'' mounting the file system.  This option is useful in
conjunction with the
.B \-v
flag to determine what the
.B mount
command is trying to do. It can also be used to add entries for devices
that were mounted earlier with the -n option.
.TP
.B \-i
Don't call the /sbin/mount.<filesystem> helper even if it exists.
.TP
.B \-l
Add the ext2, ext3 and XFS labels in the mount output. Mount must have
permission to read the disk device (e.g. be suid root) for this to work.
One can set such a label for ext2 or ext3 using the
.BR e2label (8)
utility, or for XFS using
.BR xfs_admin (8).
.TP
.B \-n
Mount without writing in
.IR /etc/mtab .
This is necessary for example when
.I /etc
is on a read-only file system.
.TP
.BI \-p " num"
In case of a loop mount with encryption, read the passphrase from
file descriptor
.I num
instead of from the terminal.
.TP
.B \-s
Tolerate sloppy mount options rather than failing. This will ignore
mount options not supported by a filesystem type. Not all filesystems
support this option. This option exists for support of the Linux
autofs\-based automounter.
.TP
.B \-r
Mount the file system read-only. A synonym is
.BR "\-o ro" .
.TP
.B \-w
Mount the file system read/write. This is the default. A synonym is
.BR "\-o rw" .
.TP
.BI \-L " label"
Mount the partition that has the specified
.IR label .
.TP
.BI \-U " uuid"
Mount the partition that has the specified
.IR uuid .
These two options require the file
.I /proc/partitions
(present since Linux 2.1.116) to exist.
.TP
.BI \-t " vfstype"
The argument following the
.B \-t
is used to indicate the file system type.  The file system types which are
currently supported are:
.IR adfs ,
.IR affs ,
.IR autofs ,
.IR coda ,
.IR coherent ,
.IR cramfs ,
.IR devpts ,
.IR efs ,
.IR ext ,
.IR ext2 ,
.IR ext3 ,
.IR hfs ,
.IR hpfs ,
.IR iso9660 ,
.IR jfs ,
.IR minix ,
.IR msdos ,
.IR ncpfs ,
.IR nfs ,
.IR ntfs ,
.IR proc ,
.IR qnx4 ,
.IR ramfs ,
.IR reiserfs ,
.IR romfs ,
.IR smbfs ,
.IR sysv ,
.IR tmpfs ,
.IR udf ,
.IR ufs ,
.IR umsdos ,
.IR usbfs ,
.IR vfat ,
.IR xenix ,
.IR xfs ,
.IR xiafs .
Note that coherent, sysv and xenix are equivalent and that
.I xenix
and
.I coherent
will be removed at some point in the future \(em use
.I sysv
instead. Since kernel version 2.1.21 the types
.I ext
and
.I xiafs
do not exist anymore. Earlier,
.I usbfs
was known as
.IR usbdevfs .

For most types all the
.B mount
program has to do is issue a simple
.IR mount (2)
system call, and no detailed knowledge of the filesystem type is required.
For a few types however (like nfs, smbfs, ncpfs) ad hoc code is
necessary. The nfs ad hoc code is built in, but smbfs and ncpfs
have a separate mount program. In order to make it possible to
treat all types in a uniform way, mount will execute the program
.I /sbin/mount.TYPE
(if that exists) when called with type
.IR TYPE .
Since various versions of the
.I smbmount
program have different calling conventions,
.I /sbin/mount.smbfs
may have to be a shell script that sets up the desired call.

If no
.B \-t
option is given, or if the
.B auto
type is specified, mount will try to guess the desired type.
If mount was compiled with the blkid library, the guessing is done
by this library. Otherwise, mount guesses itself by probing the
superblock; if that does not turn up anything that looks familiar,
mount will try to read the file
.IR /etc/filesystems ,
or, if that does not exist,
.IR /proc/filesystems .
All of the filesystem types listed there will be tried,
except for those that are labeled "nodev" (e.g.,
.IR devpts ,
.I proc
and
.IR nfs ).
If
.I /etc/filesystems
ends in a line with a single * only, mount will read
.I /proc/filesystems
afterwards.

The
.B auto
type may be useful for user-mounted floppies.
Creating a file
.I /etc/filesystems
can be useful to change the probe order (e.g., to try vfat before msdos
or ext3 before ext2) or if you use a kernel module autoloader.
Warning: the probing uses a heuristic (the presence of appropriate `magic'),
and could recognize the wrong filesystem type, possibly with catastrophic
consequences. If your data is valuable, don't ask
.B mount
to guess.

More than one type may be specified in a comma separated
list.  The list of file system types can be prefixed with
.B no
to specify the file system types on which no action should be taken.