path: root/mount/mount.8

.\" Copyright (c) 1996-2004 Andries Brouwer
.\"
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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 <lch@multimania.com>: updated page
.\" 991214, Elrond <Elrond@Wunder-Nett.org>: added some docs on devpts
.\" 010714, Michael K. Johnson <johnsonm@redhat.com> added -O
.\" 010725, Nikita Danilov <NikitaDanilov@Yahoo.COM>: reiserfs options
.\" 011124, Karl Eichwalder <ke@gnu.franken.de>: tmpfs options
.\"
.TH MOUNT 8 "2004-12-16" "Linux 2.6" "Linux Programmer's Manual"
.SH NAME
mount \- mount a filesystem
.SH SYNOPSIS
.B mount
.RB [ \-lhV ]
.LP
.BI "mount \-a
.RB [ \-fFnrsvw ]
.RB [ \-t
.IR vfstype ]
.RB [ \-O
.IR optlist ]
.LP
.B mount
.RB [ \-fnrsvw ]
.RB [ \-o
.IR option [ \fB,\fPoption ]...]
.IR device | dir
.LP
.B mount
.RB [ \-fnrsvw ]
.RB [ \-t
.IB vfstype ]
.RB [ \-o
.IR options ]
.I 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 filesystem 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"
.br

.RE
This tells the kernel to attach the filesystem 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 filesystem remains mounted,
the pathname
.I dir
refers to the root of the filesystem on
.IR device .

.B The listing and help.
.RS
Three forms of invocation do not actually mount anything:
.TP
.B "mount \-h"
prints a help message
.TP
.B "mount \-V"
prints a version string
.TP
.BR "mount " [ -l "] [" "-t \fItype\fP" ]
lists all mounted filesystems (of type
.IR type ).
The option \-l adds the labels in this listing.
See below.
.RE

.B The device indication.
.RS
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
.B LABEL
or
.B UUID
(see the \-L and \-U options below).

The recommended setup is to use LABEL=<label> or UUID=<uuid> tags rather than
.B /dev/disk/by-{label,uuid}
udev symlinks in the /etc/fstab file. The tags are
more readable, robust and portable. The
.BR mount (8)
command internally uses udev
symlinks, so use the symlinks in /etc/fstab is not advantage over LABEL=/UUID=.
For more details see
.BR libblkid (3).

Note that
.BR mount (8)
uses UUIDs as strings. The UUIDs from command line or
.BR fstab (5)
are not converted to internal binary representation. The string representation
of the UUID should be based on lower case characters.

The
.I proc
filesystem 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.)
.RE

.B The /etc/fstab, /etc/mtab and /proc/mounts files.
.RS
The file
.I /etc/fstab
(see
.BR fstab (5)),
may contain lines describing what devices are usually
mounted where, using which options.
.LP
The command
.RS
.sp
.B mount \-a
.RB [ \-t
.IR type ]
.RB [ \-O
.IR optlist ]
.sp
.RE
(usually given in a bootscript) causes all filesystems 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
When mounting a filesystem mentioned in
.IR fstab
or
.IR mtab ,
it suffices to give only the device, or only the mount point.


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

The
.B mount
program does not read the
.I /etc/fstab
file if
.I device
(or LABEL/UUID) and
.I dir
are specified. For example:
.RS
.sp
.B "mount /dev/foo /dir"
.sp
.RE
If you want to override mount options from
.I /etc/fstab
you have to use:
.RS
.sp
.B "mount device|dir -o <options>"
.sp
.RE
and then the mount options from command line will be appended to
the list of options from
.IR /etc/fstab .
The usual behaviour is that the last option wins if there is more duplicated
options.

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
using the "user" option will fail.
.RE

.B The non-superuser mounts.
.RS
Normally, only the superuser can mount filesystems.
However, when
.I fstab
contains the
.B user
option on a line, anybody can mount the corresponding system.
.LP
Thus, given a line
.RS
.sp
.B "/dev/cdrom  /cd  iso9660  ro,user,noauto,unhide"
.sp
.RE
any user can mount the iso9660 filesystem found on his CDROM
using the command
.RS
.sp
.B "mount /dev/cdrom"
.sp
.RE
or
.RS
.sp
.B "mount /cd"
.sp
.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.
.RE


.B The bind mounts.
.RS
.\" 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
.I olddir newdir
.RE
or shortoption
.RS
.br
.B mount -B
.I olddir newdir
.RE
or fstab entry is:
.RS
.br
.I /olddir
.I /newdir
.B  none  bind
.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
.I olddir newdir
.RE
or shortoption
.RS
.br
.B mount -R
.I olddir newdir
.RE
.\" available since Linux 2.4.11.

Note that the filesystem mount options will remain the same as those
on the original mount point, and cannot be changed by passing the -o
option along with --bind/--rbind. The mount options can be
changed by a separate remount command, for example:

.RS
.br
.B mount --bind
.I olddir newdir
.br
.B mount -o remount,ro
.I newdir
.RE

Note that behavior of the remount operation depends on the /etc/mtab file. The
first command stores the 'bind' flag to the /etc/mtab file and the second
command reads the flag from the file.  If you have a system without the
/etc/mtab file or if you explicitly define source and target for the remount
command (then mount(8) does not read /etc/mtab), then you have to use bind flag
(or option) for the remount command too. For example:

.RS
.br
.B mount --bind
.I olddir newdir
.br
.B mount -o remount,ro,bind
.I olddir newdir
.RE
.RE

.B The move operation.
.RS
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
.I olddir newdir
.RE
or shortoption
.RS
.br
.B mount -M
.I olddir newdir
.RE
This will cause the contents which previously appeared under olddir to be
accessed under newdir.  The physical location of the files is not changed.
.RE

.B The shared subtrees operations.
.RS
Since Linux 2.6.15 it is possible to mark a mount and its submounts as shared,
private, slave or unbindable. A shared mount provides ability to create mirrors
of that mount such that mounts and umounts within any of the mirrors propagate
to the other mirror. A slave mount receives propagation from its master, but
any not vice-versa.  A private mount carries no propagation abilities.  A
unbindable mount is a private mount which cannot be cloned through a bind
operation. Detailed semantics is documented in Documentation/sharedsubtree.txt
file in the kernel source tree.

.RS
.nf
.BI "mount --make-shared " mountpoint
.BI "mount --make-slave " mountpoint
.BI "mount --make-private " mountpoint
.BI "mount --make-unbindable " mountpoint
.fi
.RE

The following commands allows one to recursively change the type of all the
mounts under a given mountpoint.

.RS
.nf
.BI "mount --make-rshared " mountpoint
.BI "mount --make-rslave " mountpoint
.BI "mount --make-rprivate " mountpoint
.BI "mount --make-runbindable " mountpoint
.fi
.RE
.RE

.SH COMMAND LINE OPTIONS
The full set of mount options used by an invocation of
.B mount
is determined by first extracting the
mount options for the filesystem 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.

Command line options available for the
.B mount
command:
.IP "\fB\-V, \-\-version\fP"
Output version.
.IP "\fB\-h, \-\-help\fP"
Print a help message.
.IP "\fB\-v, \-\-verbose\fP"
Verbose mode.
.IP "\fB\-a, \-\-all\fP"
Mount all filesystems (of the given types) mentioned in
.IR fstab .
.IP "\fB\-F, \-\-fork\fP"
(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 .
.IP "\fB\-f, \-\-fake\fP"
Causes everything to be done except for the actual system call; if it's not
obvious, this ``fakes'' mounting the filesystem.  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. The -f option checks for
existing record in /etc/mtab and fails when the record already
exists (with regular non-fake mount, this check is done by kernel).
.IP "\fB\-i, \-\-internal\-only\fP"
Don't call the /sbin/mount.<filesystem> helper even if it exists.
.IP "\fB\-l\fP"
Add the 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, ext3 or ext4 using the
.BR e2label (8)
utility, or for XFS using
.BR xfs_admin (8),
or for reiserfs using
.BR reiserfstune (8).
.IP "\fB\-n, \-\-no\-mtab\fP"
Mount without writing in
.IR /etc/mtab .
This is necessary for example when
.I /etc
is on a read-only filesystem.
.IP "\fB\-\-no\-canonicalize\fP"
Don't canonicalize paths. The mount command canonicalizes all paths 
(from command line or fstab) and stores canonicalized paths to the 
.IR /etc/mtab
file. This option can be used together with the
.B \-f
flag for already canonicalized absolut paths.
.IP "\fB\-p, \-\-pass\-fd \fInum\fP"
In case of a loop mount with encryption, read the passphrase from
file descriptor
.I num
instead of from the terminal.
.IP "\fB\-s\fP"
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.
.IP "\fB\-r, \-\-read\-only\fP"
Mount the filesystem read-only. A synonym is
.BR "\-o ro" .

Note that, depending on the filesystem type, state and kernel behavior, the
system may still write to the device. For example, Ext3 or ext4 will replay its
journal if the filesystem is dirty. To prevent this kind of write access, you
may want to mount ext3 or ext4 filesystem with "ro,noload" mount options or
set the block device to read-only mode, see command
.BR blockdev (8).
.IP "\fB\-w, \-\-rw\fP"
Mount the filesystem read/write. This is the default. A synonym is
.BR "\-o rw" .
.IP "\fB\-L \fIlabel\fP"
Mount the partition that has the specified
.IR label .
.IP "\fB\-U \fIuuid\fP"
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.
.IP "\fB\-t, \-\-types \fIvfstype\fP"
The argument following the
.B \-t
is used to indicate the filesystem type.  The filesystem types which are
currently supported include:
.IR adfs ,
.IR affs ,
.IR autofs ,
.IR cifs ,
.IR coda ,
.IR coherent ,
.IR cramfs ,
.IR debugfs ,
.IR devpts ,
.IR efs ,
.IR ext ,
.IR ext2 ,
.IR ext3 ,
.IR ext4 ,
.IR hfs ,
.IR hfsplus ,
.IR hpfs ,
.IR iso9660 ,
.IR jfs ,
.IR minix ,
.IR msdos ,
.IR ncpfs ,
.IR nfs ,
.IR nfs4 ,
.IR ntfs ,
.IR proc ,
.IR qnx4 ,
.IR ramfs ,
.IR reiserfs ,
.IR romfs ,
.IR squashfs ,
.IR smbfs ,
.IR sysv ,
.IR tmpfs ,
.IR ubifs ,
.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 .
Note, the real list of all supported filesystems depends on your
kernel.

The programs
.B mount
and
.B umount
support filesystem subtypes.  The subtype is defined by '.subtype' suffix.  For
example  'fuse.sshfs'. It's recommended to use subtype notation rather than add
any prefix to the mount source (for example 'sshfs#example.com' is
depreacated).

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, nfs4, cifs, smbfs, ncpfs) ad hoc code is
necessary. The nfs, nfs4, cifs, smbfs, and ncpfs filesystems
have a separate mount program. In order to make it possible to
treat all types in a uniform way, mount will execute the program
.BI /sbin/mount. TYPE
(if that exists) when called with type
.IR TYPE .
Since various versions of the
.B smbmount
program have different calling conventions,
.B /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.
Mount uses the blkid or volume_id library for guessing the filesystem
type; 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 filesystem types can be prefixed with
.B no
to specify the filesystem types on which no action should be taken.
(This can be meaningful with the
.B \-a
option.) For example, the command:
.RS
.RS
.sp
.B "mount \-a \-t nomsdos,ext"
.sp
.RE
mounts all filesystems except those of type
.I msdos
and
.IR ext .
.RE
.IP "\fB\-O, \-\-test-opts \fIopts\fP"
Used in conjunction with
.BR \-a ,
to limit the set of filesystems to which the
.B \-a
is applied.  Like
.B \-t
in this regard except that it is useless except in the context of
.BR \-a .
For example, the command:
.RS
.RS
.sp
.B "mount \-a \-O no_netdev"
.sp
.RE
mounts all filesystems except those which have the option
.I _netdev
specified in the options field in the
.I /etc/fstab
file.

It is different from
.B \-t
in that each option is matched exactly; a leading
.B no
at the beginning of one option does not negate the rest.

The
.B \-t
and
.B \-O
options are cumulative in effect; that is, the command
.RS
.sp
.B "mount \-a \-t ext2 \-O _netdev"
.sp
.RE
mounts all ext2 filesystems with the _netdev option, not all filesystems
that are either ext2 or have the _netdev option specified.
.RE
.IP "\fB\-o, \-\-options \fIopts\fP"
Options are specified with a
.B \-o
flag followed by a comma separated string of options. For example:
.RS
.RS
.sp
.B "mount LABEL=mydisk \-o noatime,nouser"
.sp
.RE

For more details, see
.B FILESYSTEM INDEPENDENT MOUNT OPTIONS
and
.B FILESYSTEM SPECIFIC MOUNT OPTIONS
sections.
.RE
.IP "\fB\-B, \-\-bind\fP"
Remount a subtree somewhere else (so that its contents are available
in both places). See above.
.IP "\fB\-R, \-\-rbind\fP"
Remount a subtree and all possible submounts somewhere else (so that its
contents are available in both places). See above.
.IP "\fB\-M, \-\-move\fP"
Move a subtree to some other place. See above.

.SH FILESYSTEM INDEPENDENT MOUNT OPTIONS
Some of these options are only useful when they appear in the
.I /etc/fstab
file.

Some of these options could be enabled or disabled by default
in the system kernel. To check the current setting see the options
in /proc/mounts.

The following options apply to any filesystem that is being
mounted (but not every filesystem actually honors them - e.g., the
.B sync
option today has effect only for ext2, ext3, fat, vfat and ufs):

.TP
.B async
All I/O to the filesystem should be done asynchronously. (See also the
.B sync
option.)
.TP
.B atime
Update inode access time for each access. See also the
.B strictatime
mount option.
.TP
.B noatime
Do not update inode access times on this filesystem (e.g, for faster
access on the news spool to speed up news servers).
.TP
.B auto
Can be mounted with the
.B \-a
option.
.TP
.B noauto
Can only be mounted explicitly (i.e., the
.B \-a
option will not cause the filesystem to be mounted).
.TP
\fBcontext=\fP\fIcontext\fP, \fBfscontext=\fP\fIcontext\fP, \fBdefcontext=\fP\fIcontext\fP and \fBrootcontext=\fP\fIcontext\fP
The
.BR context=
option is useful when mounting filesystems that do not support
extended attributes, such as a floppy or hard disk formatted with VFAT, or
systems that are not normally running under SELinux, such as an ext3 formatted
disk from a non-SELinux workstation. You can also use
.BR context=
on filesystems you do not trust, such as a floppy. It also helps in compatibility with
xattr-supporting filesystems on earlier 2.4.<x> kernel versions. Even where
xattrs are supported, you can save time not having to label every file by
assigning the entire disk one security context.

A commonly used option for removable media is
.BR context=system_u:object_r:removable_t .

Two other options are
.BR fscontext=
and
.BR defcontext= ,
both of which are mutually exclusive of the context option. This means you
can use fscontext and defcontext with each other, but neither can be used with
context.

The
.BR fscontext=
option works for all filesystems, regardless of their xattr
support. The fscontext option sets the overarching filesystem label to a
specific security context. This filesystem label is separate from the
individual labels on the files. It represents the entire filesystem for
certain kinds of permission checks, such as during mount or file creation.
Individual file labels are still obtained from the xattrs on the files
themselves. The context option actually sets the aggregate context that
fscontext provides, in addition to supplying the same label for individual
files.

You can set the default security context for unlabeled files using
.BR defcontext=
option. This overrides the value set for unlabeled files in the policy and requires a
filesystem that supports xattr labeling.

The
.BR rootcontext=
option allows you to explicitly label the root inode of a FS being mounted
before that FS or inode because visable to userspace. This was found to be
useful for things like stateless linux.

Note that kernel rejects any remount request that includes the context
option even if unchanged from the current context.

For more details, see
.BR selinux (8)

.TP
.B defaults
Use default options:
.BR rw ", " suid ", " dev ", " exec ", " auto ", " nouser ", and " async.
.TP
.B dev
Interpret character or block special devices on the filesystem.
.TP
.B nodev
Do not interpret character or block special devices on the file
system.
.TP
.B diratime
Update directory inode access times on this filesystem. This is the default.
.TP
.B nodiratime
Do not update directory inode access times on this filesystem.
.TP
.B dirsync
All directory updates within the filesystem should be done synchronously.
This affects the following system calls: creat, link, unlink, symlink,
mkdir, rmdir, mknod and rename.
.TP
.B exec
Permit execution of binaries.
.TP
.B noexec
Do not allow direct execution of any binaries on the mounted filesystem.
(Until recently it was possible to run binaries anyway using a command like
/lib/ld*.so /mnt/binary. This trick fails since Linux 2.4.25 / 2.6.0.)
.TP
.B group
Allow an ordinary (i.e., non-root) user to mount the filesystem if one
of his groups matches the group of the device.
This option implies the options
.BR nosuid " and " nodev
(unless overridden by subsequent options, as in the option line
.BR group,dev,suid ).
.TP
.B iversion
Every time the inode is modified, the i_version field will be incremented.
.TP
.B noiversion
Do not increment the i_version inode field.
.TP
.B mand
Allow mandatory locks on this filesystem. See
.BR fcntl (2).
.TP
.B nomand
Do not allow mandatory locks on this filesystem.
.TP
.B _netdev
The filesystem resides on a device that requires network access
(used to prevent the system from attempting to mount these filesystems
until the network has been enabled on the system).
.TP
.B nofail
Do not report errors for this device if it does not exist.
.TP
.B relatime
Update inode access times relative to modify or change time.  Access
time is only updated if the previous access time was earlier than the
current modify or change time. (Similar to noatime, but doesn't break
mutt or other applications that need to know if a file has been read
since the last time it was modified.)
.TP
.B norelatime
Do not use
.B relatime
feature. See also the
.B strictatime
mount option.
.TP
.B strictatime
Allows to explicitly requesting full atime updates. This makes it
possible for kernel to defaults to
.B relatime
or
.B noatime
but still allow userspace to override it. For more details about the default
system mount options see /proc/mounts.
.TP
.B nostrictatime
Use the kernel's default behaviour for inode access time updates.
.TP
.B suid
Allow set-user-identifier or set-group-identifier bits to take
effect.
.TP
.B nosuid
Do not allow set-user-identifier or set-group-identifier bits to take
effect. (This seems safe, but is in fact rather unsafe if you have
suidperl(1) installed.)
.TP
.B owner
Allow an ordinary (i.e., non-root) user to mount the filesystem if he
is the owner of the device.
This option implies the options
.BR nosuid " and " nodev
(unless overridden by subsequent options, as in the option line
.BR owner,dev,suid ).
.TP
.B remount
Attempt to remount an already-mounted filesystem.  This is commonly
used to change the mount flags for a filesystem, especially to make a
readonly filesystem writeable. It does not change device or mount point.

The remount functionality follows the standard way how the mount command works
with options from fstab. It means the mount command doesn't read fstab (or
mtab) only when a
.IR device
and
.IR dir
are fully specified.

.BR "mount -o remount,rw /dev/foo /dir"

After this call all old mount options are replaced and arbitrary stuff from
fstab is ignored, except the loop= option which is internally generated and
maintained by the mount command.

.BR "mount -o remount,rw  /dir"

After this call mount reads fstab (or mtab) and merges these options with
options from command line (
.B -o
).
.TP
.B ro
Mount the filesystem read-only.
.TP
.B rw
Mount the filesystem read-write.
.TP
.B sync
All I/O to the filesystem should be done synchronously. In case of media with limited number of write cycles
(e.g. some flash drives) "sync" may cause life-cycle shortening.
.TP
.B user
Allow an ordinary user to mount the filesystem.
The name of the mounting user is written to mtab so that he can unmount
the filesystem again.
This option implies the options
.BR noexec ", " nosuid ", and " nodev
(unless overridden by subsequent options, as in the option line
.BR user,exec,dev,suid ).
.TP
.B nouser
Forbid an ordinary (i.e., non-root) user to mount the filesystem.
This is the default.
.TP
.B users
Allow every user to mount and unmount the filesystem.
This option implies the options
.BR noexec ", " nosuid ", and " nodev
(unless overridden by subsequent options, as in the option line
.BR users,exec,dev,suid ).

.SH "FILESYSTEM SPECIFIC MOUNT OPTIONS"
The following options apply only to certain filesystems.
We sort them by filesystem. They all follow the
.B \-o
flag.

What options are supported depends a bit on the running kernel.
More info may be found in the kernel source subdirectory
.IR Documentation/filesystems .

.SH "Mount options for adfs"
.TP
\fBuid=\fP\fIvalue\fP and \fBgid=\fP\fIvalue\fP
Set the owner and group of the files in the filesystem (default: uid=gid=0).
.TP
\fBownmask=\fP\fIvalue\fP and \fBothmask=\fP\fIvalue\fP
Set the permission mask for ADFS 'owner' permissions and 'other' permissions,
respectively (default: 0700 and 0077, respectively).
See also
.IR /usr/src/linux/Documentation/filesystems/adfs.txt .
.SH "Mount options for affs"
.TP
\fBuid=\fP\fIvalue\fP and \fBgid=\fP\fIvalue\fP
Set the owner and group of the root of the filesystem (default: uid=gid=0,
but with option
.B uid
or
.B gid
without specified value, the uid and gid of the current process are taken).
.TP
\fBsetuid=\fP\fIvalue\fP and \fBsetgid=\fP\fIvalue\fP
Set the owner and group of all files.
.TP
.BI mode= value
Set the mode of all files to
.IR value " & 0777"
disregarding the original permissions.
Add search permission to directories that have read permission.
The value is given in octal.
.TP
.B protect
Do not allow any changes to the protection bits on the filesystem.
.TP
.B usemp
Set uid and gid of the root of the filesystem to the uid and gid
of the mount point upon the first sync or umount, and then
clear this option. Strange...
.TP
.B verbose
Print an informational message for each successful mount.
.TP
.BI prefix= string
Prefix used before volume name, when following a link.
.TP
.BI volume= string
Prefix (of length at most 30) used before '/' when following a symbolic link.
.TP
.BI reserved= value
(Default: 2.) Number of unused blocks at the start of the device.
.TP
.BI root= value
Give explicitly the location of the root block.
.TP
.BI bs= value
Give blocksize. Allowed values are 512, 1024, 2048, 4096.
.TP
.BR grpquota | noquota | quota | usrquota
These options are accepted but ignored.
(However, quota utilities may react to such strings in
.IR /etc/fstab .)

.SH "Mount options for cifs"
See the options section of the
.BR mount.cifs (8)
man page (samba-client package must be installed).

.SH "Mount options for coherent"
None.

.SH "Mount options for debugfs"
The debugfs filesystem is a pseudo filesystem, traditionally mounted on
.IR /sys/kernel/debug .
.\" or just /debug
.\" present since 2.6.11
There are no mount options.

.SH "Mount options for devpts"
The devpts filesystem is a pseudo filesystem, traditionally mounted on
.IR /dev/pts .
In order to acquire a pseudo terminal, a process opens
.IR /dev/ptmx ;
the number of the pseudo terminal is then made available to the process
and the pseudo terminal slave can be accessed as
.IR /dev/pts/ <number>.
.TP
\fBuid=\fP\fIvalue\fP and \fBgid=\fP\fIvalue\fP
This sets the owner or the group of newly created PTYs to
the specified values. When nothing is specified, they will
be set to the UID and GID of the creating process.
For example, if there is a tty group with GID 5, then
.B gid=5
will cause newly created PTYs to belong to the tty group.
.TP
.BI mode= value
Set the mode of newly created PTYs to the specified value.
The default is 0600.
A value of
.B mode=620
and
.B gid=5
makes "mesg y" the default on newly created PTYs.
.TP
\fBnewinstance
Create a private instance of devpts filesystem, such that
indices of ptys allocated in this new instance are
independent of indices created in other instances of devpts.

All mounts of devpts without this
.B newinstance
option share the same set of pty indices (i.e legacy mode).
Each mount of devpts with the
.B newinstance
option has a private set of pty indices.

This option is mainly used to support containers in the
linux kernel. It is implemented in linux kernel versions
starting with 2.6.29.  Further, this mount option is valid
only if CONFIG_DEVPTS_MULTIPLE_INSTANCES is enabled in the
kernel configuration.

To use this option effectively,
.IR /dev/ptmx
must be a symbolic link to
.IR pts/ptmx.
See
.IR Documentation/filesystems/devpts.txt
in the linux kernel source tree for details.
.TP
.BI ptmxmode= value

Set the mode for the new
.IR ptmx
device node in the devpts filesystem.

With the support for multiple instances of devpts (see
.B newinstance
option above), each instance has a private
.IR ptmx
node in the root of the devpts filesystem (typically
.IR /dev/pts/ptmx).

For compatibility with older versions of the kernel, the
default mode of the new
.IR ptmx
node is 0000.
.BI ptmxmode= value
specifies a more useful mode for the
.IR ptmx
node and is highly recommended when the
.B newinstance
option is specified.

This option is only implemented in linux kernel versions
starting with 2.6.29. Further this option is valid only if
CONFIG_DEVPTS_MULTIPLE_INSTANCES is enabled in the kernel
configuration.

.SH "Mount options for ext"
None.
Note that the `ext' filesystem is obsolete. Don't use it.
Since Linux version 2.1.21 extfs is no longer part of the kernel source.

.SH "Mount options for ext2"
The `ext2' filesystem is the standard Linux filesystem.
.\" Due to a kernel bug, it may be mounted with random mount options
.\" (fixed in Linux 2.0.4).
Since Linux 2.5.46, for most mount options the default
is determined by the filesystem superblock. Set them with
.BR tune2fs (8).
.TP
.BR acl | noacl
Support POSIX Access Control Lists (or not).
.\" requires CONFIG_EXT2_FS_POSIX_ACL
.TP
.BR bsddf | minixdf
Set the behaviour for the
.I statfs
system call. The
.B minixdf
behaviour is to return in the
.I f_blocks
field the total number of blocks of the filesystem, while the
.B bsddf
behaviour (which is the default) is to subtract the overhead blocks
used by the ext2 filesystem and not available for file storage. Thus
.nf

% mount /k -o minixdf; df /k; umount /k
Filesystem   1024-blocks  Used Available Capacity Mounted on
/dev/sda6      2630655   86954  2412169      3%   /k
% mount /k -o bsddf; df /k; umount /k
Filesystem   1024-blocks  Used Available Capacity Mounted on
/dev/sda6      2543714      13  2412169      0%   /k

.fi
(Note that this example shows that one can add command line options
to the options given in
.IR /etc/fstab .)

.TP
.BR check= { none | nocheck }
No checking is done at mount time. This is the default. This is fast.
It is wise to invoke
.BR e2fsck (8)
every now and then, e.g. at boot time.
.TP
.B debug
Print debugging info upon each (re)mount.
.TP
.BR errors= { continue | remount-ro | panic }
Define the behaviour when an error is encountered.
(Either ignore errors and just mark the filesystem erroneous and continue,
or remount the filesystem read-only, or panic and halt the system.)
The default is set in the filesystem superblock, and can be
changed using
.BR tune2fs (8).
.TP
.BR grpid | bsdgroups " and " nogrpid | sysvgroups
These options define what group id a newly created file gets.
When
.BR grpid
is set, it takes the group id of the directory in which it is created;
otherwise (the default) it takes the fsgid of the current process, unless
the directory has the setgid bit set, in which case it takes the gid
from the parent directory, and also gets the setgid bit set
if it is a directory itself.
.TP
.BR grpquota | noquota | quota | usrquota
These options are accepted but ignored.
.TP
.BR nobh
Do not attach buffer_heads to file pagecache. (Since 2.5.49.)
.TP
.BR nouid32
Disables 32-bit UIDs and GIDs.  This is for interoperability with older
kernels which only store and expect 16-bit values.
.TP
.BR oldalloc " or " orlov
Use old allocator or Orlov allocator for new inodes. Orlov is default.
.TP
\fBresgid=\fP\fIn\fP and \fBresuid=\fP\fIn\fP
The ext2 filesystem reserves a certain percentage of the available
space (by default 5%, see
.BR mke2fs (8)
and
.BR tune2fs (8)).
These options determine who can use the reserved blocks.
(Roughly: whoever has the specified uid, or belongs to the specified group.)
.TP
.BI sb= n
Instead of block 1, use block
.I n
as superblock. This could be useful when the filesystem has been damaged.
(Earlier, copies of the superblock would be made every 8192 blocks: in
block 1, 8193, 16385, ... (and one got thousands of copies on
a big filesystem). Since version 1.08,
.B mke2fs
has a \-s (sparse superblock) option to reduce the number of backup
superblocks, and since version 1.15 this is the default. Note
that this may mean that ext2 filesystems created by a recent
.B mke2fs
cannot be mounted r/w under Linux 2.0.*.)
The block number here uses 1k units. Thus, if you want to use logical
block 32768 on a filesystem with 4k blocks, use "sb=131072".
.TP
.BR user_xattr | nouser_xattr
Support "user." extended attributes (or not).
.\" requires CONFIG_EXT2_FS_XATTR


.SH "Mount options for ext3"
The ext3 filesystem is a version of the ext2 filesystem which has been
enhanced with journalling.  It supports the same options as ext2 as
well as the following additions:
.\" .TP
.\" .BR abort
.\" Mount the filesystem in abort mode, as if a fatal error has occurred.
.TP
.BR journal=update
Update the ext3 filesystem's journal to the current format.
.TP
.BR journal=inum
When a journal already exists, this option is ignored. Otherwise, it
specifies the number of the inode which will represent the ext3 filesystem's
journal file;  ext3 will create a new journal, overwriting the old contents
of the file whose inode number is
.IR inum .
.TP
.BR noload
Do not load the ext3 filesystem's journal on mounting.
.TP
.BR data= { journal | ordered | writeback }
Specifies the journalling mode for file data.  Metadata is always journaled.
To use modes other than
.B ordered
on the root filesystem, pass the mode to the kernel as boot parameter, e.g.
.IR rootflags=data=journal .
.RS
.TP
.B journal
All data is committed into the journal prior to being written into the
main filesystem.
.TP
.B ordered
This is the default mode.  All data is forced directly out to the main file
system prior to its metadata being committed to the journal.
.TP
.B writeback
Data ordering is not preserved - data may be written into the main
filesystem after its metadata has been committed to the journal.
This is rumoured to be the highest-throughput option.  It guarantees
internal filesystem integrity, however it can allow old data to appear
in files after a crash and journal recovery.
.RE
.TP
.BR barrier=0 " / "  barrier=1 "
This enables/disables barriers.  barrier=0 disables it, barrier=1 enables it.
Write barriers enforce proper on-disk ordering of journal commits, making
volatile disk write caches safe to use, at some performance penalty.  The ext3
filesystem does not enable write barriers by default.  Be sure to enable
barriers unless your disks are battery-backed one way or another.  Otherwise
you risk filesystem corruption in case of power failure.
.TP
.BI commit= nrsec
Sync all data and metadata every
.I nrsec
seconds. The default value is 5 seconds. Zero means default.
.TP
.BR user_xattr
Enable Extended User Attributes. See the
.BR attr (5)
manual page.
.TP
.BR acl
Enable POSIX Access Control Lists. See the
.BR acl (5)
manual page.

.SH "Mount options for ext4"
The ext4 filesystem is an an advanced level of the ext3 filesystem which
incorporates scalability and reliability enhancements for supporting large
filesystem.

The options
.B journal_dev, noload, data, commit, orlov, oldalloc, [no]user_xattr
.B [no]acl, bsddf, minixdf, debug, errors, data_err, grpid, bsdgroups, nogrpid
.B sysvgroups, resgid, resuid, sb, quota, noquota, grpquota, usrquota
and
.B [no]bh
are backwardly compatible with ext3 or ext2.
.TP
.BR journal_checksum
Enable checksumming of the journal transactions.  This will allow the recovery
code in e2fsck and the kernel to detect corruption in the kernel.  It is a
compatible change and will be ignored by older kernels.
.TP
.BR journal_async_commit
Commit block can be written to disk without waiting for descriptor blocks. If
enabled older kernels cannot mount the device. This will enable
'journal_checksum' internally.
.TP
.BR journal=update
Update the ext4 filesystem's journal to the current format.
.TP
.BR barrier=0 " / "  barrier=1 " / " barrier " / " nobarrier
This enables/disables the use of write barriers in the jbd code.  barrier=0
disables, barrier=1 enables.  This also requires an IO stack which can support
barriers, and if jbd gets an error on a barrier write, it will disable again
with a warning.  Write barriers enforce proper on-disk ordering of journal
commits, making volatile disk write caches safe to use, at some performance
penalty.  If your disks are battery-backed in one way or another, disabling
barriers may safely improve performance.  The mount options "barrier" and
"nobarrier" can also be used to enable or disable barriers, for consistency
with other ext4 mount options.

The ext4 filesystem enables write barriers by default.
.TP
.BI inode_readahead= n
This tuning parameter controls the maximum number of inode table blocks that
ext4's inode table readahead algorithm will pre-read into the buffer cache.
The default value is 32 blocks.
.TP
.BI stripe= n
Number of filesystem blocks that mballoc will try to use for allocation size
and alignment. For RAID5/6 systems this should be the number of data disks *
RAID chunk size in filesystem blocks.
.TP
.BR delalloc
Deferring block allocation until write-out time.
.TP
.BR nodelalloc
Disable delayed allocation. Blocks are allocation when data is copied from user
to page cache.
.TP
.BI max_batch_time= usec
Maximum amount of time ext4 should wait for additional filesystem operations to
be batch together with a synchronous write operation. Since a synchronous
write operation is going to force a commit and then a wait for the I/O
complete, it doesn't cost much, and can be a huge throughput win, we wait for a
small amount of time to see if any other transactions can piggyback on the
synchronous write. The algorithm used is designed to automatically tune for
the speed of the disk, by measuring the amount of time (on average) that it
takes to finish committing a transaction. Call this time the "commit time".
If the time that the transaction has been running is less than the commit time,
ext4 will try sleeping for the commit time to see if other operations will join
the transaction. The commit time is capped by the max_batch_time, which
defaults to 15000us (15ms). This optimization can be turned off entirely by
setting max_batch_time to 0.
.TP
.BI min_batch_time= usec
This parameter sets the commit time (as described above) to be at least
min_batch_time. It defaults to zero microseconds. Increasing this parameter
may improve the throughput of multi-threaded, synchronous workloads on very
fast disks, at the cost of increasing latency.
.TP
.BI journal_ioprio= prio
The I/O priority (from 0 to 7, where 0 is the highest priorty) which should be
used for I/O operations submitted by kjournald2 during a commit operation.
This defaults to 3, which is a slightly higher priority than the default I/O
priority.
.TP
.BR auto_da_alloc | noauto_da_alloc
Many broken applications don't use fsync() when noauto_da_alloc
replacing existing files via patterns such as

fd = open("foo.new")/write(fd,..)/close(fd)/ rename("foo.new", "foo")

or worse yet

fd = open("foo", O_TRUNC)/write(fd,..)/close(fd).

If auto_da_alloc is enabled, ext4 will detect the replace-via-rename and
replace-via-truncate patterns and force that any delayed allocation blocks are
allocated such that at the next journal commit, in the default data=ordered
mode, the data blocks of the new file are forced to disk before the rename()
operation is committed.  This provides roughly the same level of guarantees as
ext3, and avoids the "zero-length" problem that can happen when a system
crashes before the delayed allocation blocks are forced to disk.

.SH "Mount options for fat"
(Note:
.I fat
is not a separate filesystem, but a common part of the
.IR msdos ,
.I umsdos
and
.I vfat
filesystems.)
.TP
.BR blocksize= { 512 | 1024 | 2048 }
Set blocksize (default 512). This option is obsolete.
.TP
\fBuid=\fP\fIvalue\fP and \fBgid=\fP\fIvalue\fP
Set the owner and group of all files.
(Default: the uid and gid of the current process.)
.TP
.BI umask= value
Set the umask (the bitmask of the permissions that are
.B not
present). The default is the umask of the current process.
The value is given in octal.
.TP
.BI dmask= value
Set the umask applied to directories only.
The default is the umask of the current process.
The value is given in octal.
.\" Present since Linux 2.5.43.
.TP
.BI fmask= value
Set the umask applied to regular files only.
The default is the umask of the current process.
The value is given in octal.
.\" Present since Linux 2.5.43.
.TP
.BI allow_utime= value
This option controls the permission check of mtime/atime.
.RS
.TP
.B 20
If current process is in group of file's group ID, you can change timestamp.
.TP
.B 2
Other users can change timestamp.
.PP
The default is set from `dmask' option. (If the directory is writable,
.B utime(2)
is also allowed. I.e. ~dmask & 022)

Normally
.B utime(2)
checks current process is owner of the file, or it has
CAP_FOWNER capability.  But FAT filesystem doesn't have uid/gid on disk, so
normal check is too unflexible. With this option you can relax it.
.RE
.TP
.BI check= value
Three different levels of pickyness can be chosen:
.RS
.TP
.BR r [ elaxed ]
Upper and lower case are accepted and equivalent, long name parts are
truncated (e.g.
.I verylongname.foobar
becomes
.IR verylong.foo ),
leading and embedded spaces are accepted in each name part (name and extension).
.TP
.BR n [ ormal ]
Like "relaxed", but many special characters (*, ?, <, spaces, etc.) are
rejected.  This is the default.
.TP
.BR s [ trict ]
Like "normal", but names may not contain long parts and special characters
that are sometimes used on Linux, but are not accepted by MS-DOS are
rejected. (+, =, spaces, etc.)
.RE
.TP
.BI codepage= value
Sets the codepage for converting to shortname characters on FAT
and VFAT filesystems. By default, codepage 437 is used.
.TP
.BR conv= {b [ inary ]| t [ ext ]| a [ uto ]}
The
.I fat
filesystem can perform CRLF<-->NL (MS-DOS text format to UNIX text
format) conversion in the kernel. The following conversion modes are
available:
.RS
.TP
.B binary
no translation is performed.  This is the default.
.TP
.B text
CRLF<-->NL translation is performed on all files.
.TP
.B auto
CRLF<-->NL translation is performed on all files that don't have a
"well-known binary" extension. The list of known extensions can be found at
the beginning of
.I fs/fat/misc.c
(as of 2.0, the list is: exe, com, bin, app, sys, drv, ovl, ovr, obj,
lib, dll, pif, arc, zip, lha, lzh, zoo, tar, z, arj, tz, taz, tzp, tpz,
gz, tgz, deb, gif, bmp, tif, gl, jpg, pcx, tfm, vf, gf, pk, pxl, dvi).
.PP
Programs that do computed lseeks won't like in-kernel text conversion.
Several people have had their data ruined by this translation. Beware!

For filesystems mounted in binary mode, a conversion tool
(fromdos/todos) is available. This option is obsolete.
.RE
.TP
.BI cvf_format= module
Forces the driver to use the CVF (Compressed Volume File) module
.RI cvf_ module
instead of auto-detection. If the kernel supports kmod, the
cvf_format=xxx option also controls on-demand CVF module loading.
This option is obsolete.
.TP
.BI cvf_option= option
Option passed to the CVF module. This option is obsolete.
.TP
.B debug
Turn on the
.I debug
flag.  A version string and a list of filesystem parameters will be
printed (these data are also printed if the parameters appear to be
inconsistent).
.TP
.BR fat= {12 | 16 | 32 }
Specify a 12, 16 or 32 bit fat.  This overrides
the automatic FAT type detection routine.  Use with caution!
.TP
.BI iocharset= value
Character set to use for converting between 8 bit characters
and 16 bit Unicode characters. The default is iso8859-1.
Long filenames are stored on disk in Unicode format.
.TP
.BI tz=UTC
This option disables the conversion of timestamps
between local time (as used by Windows on FAT) and UTC
(which Linux uses internally).  This is particularly
useful when mounting devices (like digital cameras)
that are set to UTC in order to avoid the pitfalls of
local time.
.TP
.B quiet
Turn on the
.I quiet
flag.  Attempts to chown or chmod files do not return errors,
although they fail. Use with caution!
.TP
.B showexec
If set, the execute permission bits of the file will be allowed only if
the extension part of the name is .EXE, .COM, or .BAT. Not set by default.
.TP
.B sys_immutable
If set, ATTR_SYS attribute on FAT is handled as IMMUTABLE flag on Linux.
Not set by default.
.TP
.B flush
If set, the filesystem will try to flush to disk more early than normal.
Not set by default.
.TP
.B usefree
Use the "free clusters" value stored on FSINFO. It'll
be used to determine number of free clusters without
scanning disk. But it's not used by default, because
recent Windows don't update it correctly in some
case. If you are sure the "free clusters" on FSINFO is
correct, by this option you can avoid scanning disk.
.TP
.BR dots ", " nodots ", " dotsOK= [ yes | no ]
Various misguided attempts to force Unix or DOS conventions
onto a FAT filesystem.

.SH "Mount options for hfs"
.TP
.BI creator= cccc ", type=" cccc
Set the creator/type values as shown by the MacOS finder
used for creating new files.  Default values: '????'.
.TP
.BI uid= n ", gid=" n
Set the owner and group of all files.
(Default: the uid and gid of the current process.)
.TP
.BI dir_umask= n ", file_umask=" n ", umask=" n
Set the umask used for all directories, all regular files, or all
files and directories.  Defaults to the umask of the current process.
.TP
.BI session= n
Select the CDROM session to mount.
Defaults to leaving that decision to the CDROM driver.
This option will fail with anything but a CDROM as underlying device.
.TP
.BI part= n
Select partition number n from the device.
Only makes sense for CDROMS.
Defaults to not parsing the partition table at all.
.TP
.B quiet
Don't complain about invalid mount options.

.SH "Mount options for hpfs"
.TP
\fBuid=\fP\fIvalue\fP and \fBgid=\fP\fIvalue\fP
Set the owner and group of all files. (Default: the uid and gid
of the current process.)
.TP
.BI umask= value
Set the umask (the bitmask of the permissions that are
.B not
present). The default is the umask of the current process.
The value is given in octal.
.TP
.BR case= { lower | asis }
Convert all files names to lower case, or leave them.
(Default:
.BR case=lower .)
.TP
.BR conv= { binary | text | auto }
For
.BR conv=text ,
delete some random CRs (in particular, all followed by NL)
when reading a file.
For
.BR conv=auto ,
choose more or less at random between
.BR conv=binary " and " conv=text .
For
.BR conv=binary ,
just read what is in the file. This is the default.
.TP
.B nocheck
Do not abort mounting when certain consistency checks fail.

.SH "Mount options for iso9660"
ISO 9660 is a standard describing a filesystem structure to be used
on CD-ROMs. (This filesystem type is also seen on some DVDs. See also the
.I udf
filesystem.)

Normal
.I iso9660
filenames appear in a 8.3 format (i.e., DOS-like restrictions on filename
length), and in addition all characters are in upper case.  Also there is
no field for file ownership, protection, number of links, provision for
block/character devices, etc.

Rock Ridge is an extension to iso9660 that provides all of these unix like
features.  Basically there are extensions to each directory record that
supply all of the additional information, and when Rock Ridge is in use,
the filesystem is indistinguishable from a normal UNIX filesystem (except
that it is read-only, of course).
.TP
.B norock
Disable the use of Rock Ridge extensions, even if available. Cf.\&
.BR map .
.TP
.B nojoliet
Disable the use of Microsoft Joliet extensions, even if available. Cf.\&
.BR map .
.TP
.BR check= { r [ elaxed ]| s [ trict ]}
With
.BR check=relaxed ,
a filename is first converted to lower case before doing the lookup.
This is probably only meaningful together with
.B norock
and
.BR map=normal .
(Default:
.BR check=strict .)
.TP
\fBuid=\fP\fIvalue\fP and \fBgid=\fP\fIvalue\fP
Give all files in the filesystem the indicated user or group id,
possibly overriding the information found in the Rock Ridge extensions.
(Default:
.BR uid=0,gid=0 .)
.TP
.BR map= { n [ ormal ]| o [ ff ]| a [ corn ]}
For non-Rock Ridge volumes, normal name translation maps upper
to lower case ASCII, drops a trailing `;1', and converts `;' to `.'.
With
.B map=off
no name translation is done. See
.BR norock .
(Default:
.BR map=normal .)
.B map=acorn
is like
.BR map=normal
but also apply Acorn extensions if present.
.TP
.BI mode= value
For non-Rock Ridge volumes, give all files the indicated mode.
(Default: read permission for everybody.)
Since Linux 2.1.37 one no longer needs to specify the mode in
decimal. (Octal is indicated by a leading 0.)
.TP
.B unhide
Also show hidden and associated files.
(If the ordinary files and the associated or hidden files have
the same filenames, this may make the ordinary files inaccessible.)
.TP
.BR block= { 512 | 1024 | 2048 }
Set the block size to the indicated value.
(Default:
.BR block=1024 .)
.TP
.BR conv= { a [ uto ]| b [ inary ]| m [ text ]| t [ ext ]}
(Default:
.BR conv=binary .)
Since Linux 1.3.54 this option has no effect anymore.
(And non-binary settings used to be very dangerous,
possibly leading to silent data corruption.)
.TP
.B cruft
If the high byte of the file length contains other garbage,
set this mount option to ignore the high order bits of the file length.
This implies that a file cannot be larger than 16MB.
.TP
.BI session= x
Select number of session on multisession CD. (Since 2.3.4.)
.TP
.BI sbsector= xxx
Session begins from sector xxx. (Since 2.3.4.)
.LP
The following options are the same as for vfat and specifying them only makes
sense when using discs encoded using Microsoft's Joliet extensions.
.TP
.BI iocharset= value
Character set to use for converting 16 bit Unicode characters on CD
to 8 bit characters. The default is iso8859-1.
.TP
.B utf8
Convert 16 bit Unicode characters on CD to UTF-8.

.SH "Mount options for jfs"
.TP
.BI iocharset= name
Character set to use for converting from Unicode to ASCII.  The default is
to do no conversion.  Use
.B iocharset=utf8
for UTF8 translations.  This requires CONFIG_NLS_UTF8 to be set in
the kernel
.I ".config"
file.
.TP
.BI resize= value
Resize the volume to
.I value
blocks. JFS only supports growing a volume, not shrinking it. This option
is only valid during a remount, when the volume is mounted read-write. The
.B resize
keyword with no value will grow the volume to the full size of the partition.
.TP
.B nointegrity
Do not write to the journal.  The primary use of this option is to allow
for higher performance when restoring a volume from backup media. The
integrity of the volume is not guaranteed if the system abnormally abends.
.TP
.B integrity
Default.  Commit metadata changes to the journal.  Use this option to remount
a volume where the
.B nointegrity
option was previously specified in order to restore normal behavior.
.TP
.BR errors= { continue | remount-ro | panic }
Define the behaviour when an error is encountered.
(Either ignore errors and just mark the filesystem erroneous and continue,
or remount the filesystem read-only, or panic and halt the system.)
.TP
.BR noquota | quota | usrquota | grpquota
These options are accepted but ignored.

.SH "Mount options for minix"
None.

.SH "Mount options for msdos"
See mount options for fat.
If the
.I msdos
filesystem detects an inconsistency, it reports an error and sets the file
system read-only. The filesystem can be made writeable again by remounting
it.

.SH "Mount options for ncpfs"
Just like
.IR nfs ", the " ncpfs
implementation expects a binary argument (a
.IR "struct ncp_mount_data" )
to the mount system call. This argument is constructed by
.BR ncpmount (8)
and the current version of
.B mount
(2.12) does not know anything about ncpfs.

.SH "Mount options for nfs and nfs4"
See the options section of the
.BR nfs (5)
man page (nfs-utils package must be installed).

The
.IR nfs " and " nfs4
implementation expects a binary argument (a
.IR "struct nfs_mount_data" )
to the mount system call. This argument is constructed by
.BR mount.nfs (8)
and the current version of
.B mount
(2.13) does not know anything about nfs and nfs4.

.SH "Mount options for ntfs"
.TP
.BI iocharset= name
Character set to use when returning file names.
Unlike VFAT, NTFS suppresses names that contain
unconvertible characters. Deprecated.
.\" since 2.5.11
.TP
.BI nls= name
New name for the option earlier called
.IR iocharset .
.\" since 2.5.11
.TP
.BR utf8
Use UTF-8 for converting file names.
.TP
.BR uni_xlate= { 0 | 1 | 2 }
For 0 (or `no' or `false'), do not use escape sequences
for unknown Unicode characters.
For 1 (or `yes' or `true') or 2, use vfat-style 4-byte escape sequences
starting with ":". Here 2 give a little-endian encoding
and 1 a byteswapped bigendian encoding.
.TP
.B posix=[0|1]
If enabled (posix=1), the filesystem distinguishes between
upper and lower case. The 8.3 alias names are presented as
hard links instead of being suppressed. This option is obsolete.
.TP
\fBuid=\fP\fIvalue\fP, \fBgid=\fP\fIvalue\fP and \fBumask=\fP\fIvalue\fP
Set the file permission on the filesystem.
The umask value is given in octal.
By default, the files are owned by root and not readable by somebody else.

.SH "Mount options for proc"
.TP
\fBuid=\fP\fIvalue\fP and \fBgid=\fP\fIvalue\fP
These options are recognized, but have no effect as far as I can see.

.SH "Mount options for ramfs"
Ramfs is a memory based filesystem. Mount it and you have it. Unmount it
and it is gone. Present since Linux 2.3.99pre4.
There are no mount options.

.SH "Mount options for reiserfs"
Reiserfs is a journaling filesystem.
.TP
.BR conv
Instructs version 3.6 reiserfs software to mount a version 3.5 filesystem,
using the 3.6 format for newly created objects. This filesystem will no
longer be compatible with reiserfs 3.5 tools.
.TP
.BR hash= { rupasov | tea | r5 | detect }
Choose which hash function reiserfs will use to find files within directories.
.RS
.TP
.B rupasov
A hash invented by Yury Yu. Rupasov.  It is fast and preserves locality,
mapping lexicographically close file names to close hash values.
This option should not be used, as it causes a high probability of hash
collisions.
.TP
.B tea
A Davis-Meyer function implemented by Jeremy Fitzhardinge.
It uses hash permuting bits in the name.  It gets high randomness
and, therefore, low probability of hash collisions at some CPU cost.
This may be used if EHASHCOLLISION errors are experienced with the r5 hash.
.TP
.B r5
A modified version of the rupasov hash. It is used by default and is
the best choice unless the filesystem has huge directories and
unusual file-name patterns.
.TP
.B detect
Instructs
.IR mount
to detect which hash function is in use by examining
the filesystem being mounted,  and to write this information into
the reiserfs superblock. This is only useful on the first mount of
an old format filesystem.
.RE
.TP
.BR hashed_relocation
Tunes the block allocator. This may provide performance improvements
in some situations.
.TP
.BR no_unhashed_relocation
Tunes the block allocator. This may provide performance improvements
in some situations.
.TP
.BR noborder
Disable the border allocator algorithm invented by Yury Yu. Rupasov.
This may provide performance improvements in some situations.
.TP
.BR nolog
Disable journalling. This will provide slight performance improvements in
some situations at the cost of losing reiserfs's fast recovery from crashes.
Even with this option turned on, reiserfs still performs all journalling
operations, save for actual writes into its journalling area.  Implementation
of
.IR nolog
is a work in progress.
.TP
.BR notail
By default, reiserfs stores small files and `file tails' directly into its
tree. This confuses some utilities such as
.BR LILO (8).
This option is used to disable packing of files into the tree.
.TP
.BR replayonly
Replay the transactions which are in the journal, but do not actually
mount the filesystem. Mainly used by
.IR reiserfsck .
.TP
.BI resize= number
A remount option which permits online expansion of reiserfs partitions.
Instructs reiserfs to assume that the device has
.I number
blocks.
This option is designed for use with devices which are under logical
volume management (LVM).
There is a special
.I resizer
utility which can be obtained from
.IR ftp://ftp.namesys.com/pub/reiserfsprogs .
.TP
.BR user_xattr
Enable Extended User Attributes. See the
.BR attr (5)
manual page.
.TP
.BR acl
Enable POSIX Access Control Lists. See the
.BR acl (5)
manual page.
.TP
.BR barrier=none " / "  barrier=flush "
This enables/disables the use of write barriers in the journaling code.
barrier=none disables it, barrier=flush enables it. Write barriers enforce
proper on-disk ordering of journal commits, making volatile disk write caches
safe to use, at some performance penalty. The reiserfs filesystem does not
enable write barriers by default. Be sure to enable barriers unless your disks
are battery-backed one way or another. Otherwise you risk filesystem
corruption in case of power failure.

.SH "Mount options for romfs"
None.

.SH "Mount options for squashfs"
None.

.SH "Mount options for smbfs"
Just like
.IR nfs ", the " smbfs
implementation expects a binary argument (a
.IR "struct smb_mount_data" )
to the mount system call. This argument is constructed by
.BR smbmount (8)
and the current version of
.B mount
(2.12) does not know anything about smbfs.

.SH "Mount options for sysv"
None.

.SH "Mount options for tmpfs"
.TP
.BI size= nbytes
Override default maximum size of the filesystem.
The size is given in bytes, and rounded up to entire pages.
The default is half of the memory. The size parameter also accepts a suffix %
to limit this tmpfs instance to that percentage of your physical RAM:
the default, when neither size nor nr_blocks is specified, is size=50%
.TP
.B nr_blocks=
The same as size, but in blocks of PAGE_CACHE_SIZE
.TP
.B nr_inodes=
The maximum number of inodes for this instance. The default
is half of the number of your physical RAM pages, or (on a
machine with highmem) the number of lowmem RAM pages,
whichever is the lower.
.PP
The tmpfs mount options for sizing (
.BR size ,
.BR nr_blocks ,
and
.BR nr_inodes )
accept a suffix
.BR k ,
.B m
or
.B g
for Ki, Mi, Gi (binary kilo, mega and giga) and can be changed on remount.

.TP
.B mode=
Set initial permissions of the root directory.
.TP
.B uid=
The user id.
.TP
.B gid=
The group id.
.TP
.B mpol=[default|prefer:Node|bind:NodeList|interleave|interleave:NodeList]
Set the NUMA memory allocation policy for all files in that
instance (if the kernel CONFIG_NUMA is enabled) - which can be adjusted on the
fly via 'mount -o remount ...'
.RS
.TP
.B default
prefers to allocate memory from the local node
.TP
.B prefer:Node
prefers to allocate memory from the given Node
.TP
.B bind:NodeList
allocates memory only from nodes in NodeList
.TP
.B interleave
prefers to allocate from each node in turn
.TP
.B interleave:NodeList
allocates from each node of NodeList in turn.
.PP
The NodeList format is a comma-separated list of decimal numbers and ranges, a
range being two hyphen-separated decimal numbers, the smallest and largest node
numbers in the range.  For example, mpol=bind:0-3,5,7,9-15

Note that trying to mount a tmpfs with an mpol option will fail if the
running kernel does not support NUMA; and will fail if its nodelist
specifies a node which is not online.  If your system relies on that
tmpfs being mounted, but from time to time runs a kernel built without
NUMA capability (perhaps a safe recovery kernel), or with fewer nodes
online, then it is advisable to omit the mpol option from automatic
mount options.  It can be added later, when the tmpfs is already mounted
on MountPoint, by 'mount -o remount,mpol=Policy:NodeList MountPoint'.
.PE

.SH "Mount options for ubifs"
UBIFS is a flash file system which works on top of UBI volumes. Note that
.B
atime
is not supported and is always turned off.
.TP
The device name may be specified as
.RS
.B ubiX_Y
UBI device number
.BR X ,
volume number
.B Y
.TP
.B ubiY
UBI device number
.BR 0 ,
volume number
.B Y
.TP
.B ubiX:NAME
UBI device number
.BR X ,
volume with name
.B NAME
.TP
.B ubi:NAME
UBI device number
.BR 0 ,
volume with name
.B NAME
.RE
Alternative
.B !
separator may be used instead of
.BR : .
.TP
The following mount options are available:
.TP
.BR bulk_read
Enable bulk-read. VFS read-ahead is disabled because it slows down the file
system. Bulk-Read is an internal optimization. Some flashes may read faster if
the data are read at one go, rather than at several read requests. For
example, OneNAND can do "read-while-load" if it reads more than one NAND page.
.TP
.BR no_bulk_read
Do not bulk-read. This is the default.
.TP
.BR chk_data_crc
Check data CRC-32 checksums. This is the default.
.TP
.BR no_chk_data_crc.
Do not check data CRC-32 checksums. With this option, the filesystem does not
check CRC-32 checksum for data, but it does check it for the internal indexing
information. This option only affects reading, not writing. CRC-32 is always
calculated when writing the data.
.TP
.BR compr= { none | lzo | zlib }
Select the default compressor which is used when new files are written. It is
still possible to read compressed files if mounted with the
.B none
option.

.SH "Mount options for udf"
udf is the "Universal Disk Format" filesystem defined by the Optical
Storage Technology Association, and is often used for DVD-ROM.
See also
.IR iso9660 .
.TP
.B gid=
Set the default group.
.TP
.B umask=
Set the default umask.
The value is given in octal.
.TP
.B uid=
Set the default user.
.TP
.B unhide
Show otherwise hidden files.
.TP
.B undelete
Show deleted files in lists.
.TP
.B nostrict
Unset strict conformance.
.\" .TP
.\" .B utf8
.\" (unused).
.TP
.B iocharset
Set the NLS character set.
.TP
.B bs=
Set the block size. (May not work unless 2048.)
.TP
.B novrs
Skip volume sequence recognition.
.TP
.B session=
Set the CDROM session counting from 0. Default: last session.
.TP
.B anchor=
Override standard anchor location. Default: 256.
.TP
.B volume=
Override the VolumeDesc location. (unused)
.TP
.B partition=
Override the PartitionDesc location. (unused)
.TP
.B lastblock=
Set the last block of the filesystem.
.TP
.B fileset=
Override the fileset block location. (unused)
.TP
.B rootdir=
Override the root directory location. (unused)

.SH "Mount options for ufs"
.TP
.BI ufstype= value
UFS is a filesystem widely used in different operating systems.
The problem are differences among implementations. Features of some
implementations are undocumented, so its hard to recognize the
type of ufs automatically.
That's why the user must specify the type of ufs by mount option.
Possible values are:
.RS
.TP
.B old
Old format of ufs, this is the default, read only.
(Don't forget to give the \-r option.)
.TP
.B 44bsd
For filesystems created by a BSD-like system (NetBSD,FreeBSD,OpenBSD).
.TP
.B sun
For filesystems created by SunOS or Solaris on Sparc.
.TP
.B sunx86
For filesystems created by Solaris on x86.
.TP
.B hp
For filesystems created by HP-UX, read-only.
.TP
.B nextstep
For filesystems created by NeXTStep (on NeXT station) (currently read only).
.TP
.B nextstep-cd
For NextStep CDROMs (block_size == 2048), read-only.
.TP
.B openstep
For filesystems created by OpenStep (currently read only).
The same filesystem type is also used by Mac OS X.
.RE

.TP
.BI onerror= value
Set behaviour on error:
.RS
.TP
.B panic
If an error is encountered, cause a kernel panic.
.TP
.RB [ lock | umount | repair ]
These mount options don't do anything at present;
when an error is encountered only a console message is printed.
.RE

.SH "Mount options for umsdos"
See mount options for msdos.
The
.B dotsOK
option is explicitly killed by
.IR umsdos .

.SH "Mount options for vfat"
First of all, the mount options for
.I fat
are recognized.
The
.B dotsOK
option is explicitly killed by
.IR vfat .
Furthermore, there are
.TP
.B uni_xlate
Translate unhandled Unicode characters to special escaped sequences.
This lets you backup and restore filenames that are created with any
Unicode characters. Without this option, a '?' is used when no
translation is possible. The escape character is ':' because it is
otherwise illegal on the vfat filesystem. The escape sequence
that gets used, where u is the unicode character,
is: ':', (u & 0x3f), ((u>>6) & 0x3f), (u>>12).
.TP
.B posix
Allow two files with names that only differ in case.
This option is obsolete.
.TP
.B nonumtail
First try to make a short name without sequence number,
before trying
.IR name~num.ext .
.TP
.B utf8
UTF8 is the filesystem safe 8-bit encoding of Unicode that is used by the
console. It can be be enabled for the filesystem with this option or disabled
with utf8=0, utf8=no or utf8=false. If `uni_xlate' gets set, UTF8 gets
disabled.
.TP
.BR shortname= { lower | win95 | winnt | mixed }

Defines the behaviour for creation and display of filenames which fit into
8.3 characters. If a long name for a file exists, it will always be
preferred display. There are four modes:
:
.RS
.TP
.I lower
Force the short name to lower case upon display; store a long name when
the short name is not all upper case.
.TP
.I win95
Force the short name to upper case upon display; store a long name when
the short name is not all upper case.
.TP
.I winnt
Display the shortname as is; store a long name when the short name is
not all lower case or all upper case.
.TP
.I mixed
Display the short name as is; store a long name when the short name is not
all upper case. This mode is the default since Linux 2.6.32.
.RE


.SH "Mount options for usbfs"
.TP
\fBdevuid=\fP\fIuid\fP and \fBdevgid=\fP\fIgid\fP and \fBdevmode=\fP\fImode\fP
Set the owner and group and mode of the device files in the usbfs filesystem
(default: uid=gid=0, mode=0644). The mode is given in octal.
.TP
\fBbusuid=\fP\fIuid\fP and \fBbusgid=\fP\fIgid\fP and \fBbusmode=\fP\fImode\fP
Set the owner and group and mode of the bus directories in the usbfs
filesystem (default: uid=gid=0, mode=0555). The mode is given in octal.
.TP
\fBlistuid=\fP\fIuid\fP and \fBlistgid=\fP\fIgid\fP and \fBlistmode=\fP\fImode\fP
Set the owner and group and mode of the file
.I devices
(default: uid=gid=0, mode=0444). The mode is given in octal.

.SH "Mount options for xenix"
None.

.SH "Mount options for xfs"
.TP
.BI allocsize= size
Sets the buffered I/O end-of-file preallocation size when
doing delayed allocation writeout (default size is 64KiB).
Valid values for this option are page size (typically 4KiB)
through to 1GiB, inclusive, in power-of-2 increments.
.TP
.BR attr2 | noattr2
The options enable/disable (default is enabled) an "opportunistic"
improvement to be made in the way inline extended attributes are
stored on-disk.
When the new form is used for the first time (by setting or
removing extended attributes) the on-disk superblock feature
bit field will be updated to reflect this format being in use.
.TP
.B barrier
Enables the use of block layer write barriers for writes into
the journal and unwritten extent conversion.  This allows for
drive level write caching to be enabled, for devices that
support write barriers.
.TP
.B dmapi
Enable the DMAPI (Data Management API) event callouts.
Use with the
.B mtpt
option.
.TP
.BR grpid | bsdgroups " and " nogrpid | sysvgroups
These options define what group ID a newly created file gets.
When grpid is set, it takes the group ID of the directory in
which it is created; otherwise (the default) it takes the fsgid
of the current process, unless the directory has the setgid bit
set, in which case it takes the gid from the parent directory,
and also gets the setgid bit set if it is a directory itself.
.TP
.BI ihashsize= value
Sets the number of hash buckets available for hashing the
in-memory inodes of the specified mount point.  If a value
of zero is used, the value selected by the default algorithm
will be displayed in
.IR /proc/mounts .
.TP
.BR ikeep | noikeep
When inode clusters are emptied of inodes, keep them around
on the disk (ikeep) - this is the traditional XFS behaviour
and is still the default for now.  Using the noikeep option,
inode clusters are returned to the free space pool.
.TP
.B inode64
Indicates that XFS is allowed to create inodes at any location
in the filesystem, including those which will result in inode
numbers occupying more than 32 bits of significance.  This is
provided for backwards compatibility, but causes problems for
backup applications that cannot handle large inode numbers.
.TP
.BR largeio | nolargeio
If
.B nolargeio
is specified, the optimal I/O reported in
st_blksize by
.BR stat (2)
will be as small as possible to allow user
applications to avoid inefficient read/modify/write I/O.
If
.B largeio
is specified, a filesystem that has a
.B swidth
specified
will return the
.B swidth
value (in bytes) in st_blksize. If the
filesystem does not have a
.B swidth
specified but does specify
an
.B allocsize
then
.B allocsize
(in bytes) will be returned
instead.
If neither of these two options are specified, then filesystem
will behave as if
.B nolargeio
was specified.
.TP
.BI logbufs= value
Set the number of in-memory log buffers.  Valid numbers range
from 2-8 inclusive.
The default value is 8 buffers for any recent kernel.
.TP
.BI logbsize= value
Set the size of each in-memory log buffer.
Size may be specified in bytes, or in kilobytes with a "k" suffix.
Valid sizes for version 1 and version 2 logs are 16384 (16k) and
32768 (32k).  Valid sizes for version 2 logs also include
65536 (64k), 131072 (128k) and 262144 (256k).
The default value for any recent kernel is 32768.
.TP
\fBlogdev=\fP\fIdevice\fP and \fBrtdev=\fP\fIdevice\fP
Use an external log (metadata journal) and/or real-time device.
An XFS filesystem has up to three parts: a data section, a log section,
and a real-time section.
The real-time section is optional, and the log section can be separate
from the data section or contained within it.
Refer to
.BR xfs (5).
.TP
.BI  mtpt= mountpoint
Use with the
.B dmapi
option. The value specified here will be
included in the DMAPI mount event, and should be the path of
the actual mountpoint that is used.
.TP
.B noalign
Data allocations will not be aligned at stripe unit boundaries.
.TP
.B noatime
Access timestamps are not updated when a file is read.
.TP
.B norecovery
The filesystem will be mounted without running log recovery.
If the filesystem was not cleanly unmounted, it is likely to
be inconsistent when mounted in
.B norecovery
mode.
Some files or directories may not be accessible because of this.
Filesystems mounted
.B norecovery
must be mounted read-only or the mount will fail.
.TP
.B nouuid
Don't check for double mounted filesystems using the filesystem uuid.
This is useful to mount LVM snapshot volumes.
.TP
.B osyncisosync
Make O_SYNC writes implement true O_SYNC.  WITHOUT this option,
Linux XFS behaves as if an
.B osyncisdsync
option is used,
which will make writes to files opened with the O_SYNC flag set
behave as if the O_DSYNC flag had been used instead.
This can result in better performance without compromising
data safety.
However if this option is not in effect, timestamp updates from
O_SYNC writes can be lost if the system crashes.
If timestamp updates are critical, use the
.B osyncisosync
option.
.TP
.BR uquota | usrquota | uqnoenforce | quota
User disk quota accounting enabled, and limits (optionally)
enforced.  Refer to
.BR xfs_quota (8)
for further details.
.TP
.BR gquota | grpquota | gqnoenforce
Group disk quota accounting enabled and limits (optionally)
enforced. Refer to
.BR xfs_quota (8)
for further details.
.TP
.BR pquota | prjquota | pqnoenforce
Project disk quota accounting enabled and limits (optionally)
enforced. Refer to
.BR xfs_quota (8)
for further details.
.TP
\fBsunit=\fP\fIvalue\fP and \fBswidth=\fP\fIvalue\fP
Used to specify the stripe unit and width for a RAID device or a stripe
volume.
.I value
must be specified in 512-byte block units.
If this option is not specified and the filesystem was made on a stripe
volume or the stripe width or unit were specified for the RAID device at
mkfs time, then the mount system call will restore the value from the
superblock.
For filesystems that are made directly on RAID devices, these options can be
used to override the information in the superblock if the underlying disk
layout changes after the filesystem has been created.
The
.B swidth
option is required if the
.B sunit
option has been specified,
and must be a multiple of the
.B sunit
value.
.TP
.B swalloc
Data allocations will be rounded up to stripe width boundaries
when the current end of file is being extended and the file
size is larger than the stripe width size.

.SH "Mount options for xiafs"
None. Although nothing is wrong with xiafs, it is not used much,
and is not maintained. Probably one shouldn't use it.
Since Linux version 2.1.21 xiafs is no longer part of the kernel source.

.SH "THE LOOP DEVICE"
One further possible type is a mount via the loop device. For example,
the command
.RS
.sp
.B "mount /tmp/disk.img /mnt -t vfat -o loop=/dev/loop"
.sp
.RE
will set up the loop device
.I /dev/loop3
to correspond to the file
.IR /tmp/disk.img ,
and then mount this device on
.IR /mnt .

If no explicit loop device is mentioned
(but just an option `\fB\-o loop\fP' is given), then
.B mount
will try to find some unused loop device and use that, for example
.RS
.sp
.B "mount /tmp/disk.img /mnt -o loop"
.sp
.RE
The mount command
.B automatically
creates a loop device from a regular file if a filesystem type is
not specified or the filesystem is known for libblkid, for example:
.RS
.sp
.B "mount /tmp/disk.img /mnt"
.sp
.B "mount -t ext3 /tmp/disk.img /mnt"
.sp
.RE
This type of mount knows about four options, namely
.BR loop ", " offset ", " sizelimit " and " encryption ,
that are really options to
.BR \%losetup (8).
(These options can be used in addition to those specific
to the filesystem type.)

Since Linux 2.6.25 is supported auto-destruction of loop devices and
then any loop device allocated by
.B mount
will be freed by
.B umount
independently on
.IR /etc/mtab .

You can also free a loop device by hand, using `losetup -d' or `umount -d`.

.SH RETURN CODES
.B mount
has the following return codes (the bits can be ORed):
.TP
.BR 0
success
.TP
.BR 1
incorrect invocation or permissions
.TP
.BR 2
system error (out of memory, cannot fork, no more loop devices)
.TP
.BR 4
internal
.B mount
bug
.TP
.BR 8
user interrupt
.TP
.BR 16
problems writing or locking /etc/mtab
.TP
.BR 32
mount failure
.TP
.BR 64
some mount succeeded

.SH NOTES
The syntax of external mount helpers is:

.RS
.BI /sbin/mount. <suffix>
.I spec dir
.RB [ \-sfnv ]
.RB [ \-o
.IR options ]
.RB [ \-t
.IR type.subtype ]
.RE

where the <type> is filesystem type and \-sfnvo options have same meaning like
standard mount options. The \-t option is used  for filesystems with subtypes
support (for example /sbin/mount.fuse -t fuse.sshfs).

.SH FILES
.TP 18n
.I /etc/fstab
filesystem table
.TP
.I /etc/mtab
table of mounted filesystems
.TP
.I /etc/mtab~
lock file
.TP
.I /etc/mtab.tmp
temporary file
.TP
.I /etc/filesystems
a list of filesystem types to try

.SH "SEE ALSO"
.BR mount (2),
.BR umount (2),
.BR fstab (5),
.BR umount (8),
.BR swapon (8),
.BR nfs (5),
.BR xfs (5),
.BR e2label (8),
.BR xfs_admin (8),
.BR mountd (8),
.BR nfsd (8),
.BR mke2fs (8),
.BR tune2fs (8),
.BR losetup (8)
.SH BUGS
It is possible for a corrupted filesystem to cause a crash.
.PP
Some Linux filesystems don't support
.B "\-o sync and \-o dirsync"
(the ext2, ext3, fat and vfat filesystems
.I do
support synchronous updates (a la BSD) when mounted with the
.B sync
option).
.PP
The
.B "\-o remount"
may not be able to change mount parameters (all
.IR ext2fs -specific
parameters, except
.BR  sb ,
are changeable with a remount, for example, but you can't change
.B gid
or
.B umask
for the
.IR fatfs ).
.PP
Mount by label or uuid will work only if your devices have the names listed in
.IR /proc/partitions .
In particular, it may well fail if the kernel was compiled with devfs
but devfs is not mounted.
.PP
It is possible that files
.IR /etc/mtab
and
.IR /proc/mounts
don't match. The first file is based only on the mount command options, but the
content of the second file also depends on the kernel and others settings (e.g.
remote NFS server. In particular case the mount command may reports unreliable
information about a NFS mount point and the /proc/mounts file usually contains
more reliable information.)
.PP
Checking files on NFS filesystem referenced by file descriptors (i.e. the
.BR fcntl
and
.BR ioctl
families of functions) may lead to inconsistent result due to the lack of
consistency check in kernel even if noac is used.
.SH HISTORY
A
.B mount
command existed in Version 5 AT&T UNIX.
.SH AVAILABILITY
The mount command is part of the util-linux-ng package and is available from
ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.