MOUNT(8) System Administration MOUNT(8)
mount - mount a filesystem
mount [-l|-h|-V]
mount -a [-fFnrsvw] [-t fstype] [-O optlist]
mount [-fnrsvw] [-o options] device|dir
mount [-fnrsvw] [-t fstype] [-o options] device dir
All files accessible in a Unix system are arranged in one big tree,
the file hierarchy, rooted at /. These files can be spread out over
several devices. The mount command serves to attach the filesystem
found on some device to the big file tree. Conversely, the umount(8)
command will detach it again. The filesystem is used to control how
data is stored on the device or provided in a virtual way by network
or another services.
The standard form of the mount command is:
mount -t type device dir
This tells the kernel to attach the filesystem found on device (which
is of type type) at the directory dir. The option -t type is
optional. The mount command is usually able to detect a filesystem.
The root permissions are necessary to mount a filesystem by default.
See section "Non-superuser mounts" below for more details. The
previous contents (if any) and owner and mode of dir become
invisible, and as long as this filesystem remains mounted, the
pathname dir refers to the root of the filesystem on device.
If only the directory or the device is given, for example:
mount /dir
then mount looks for a mountpoint (and if not found then for a
device) in the /etc/fstab file. It's possible to use the --target or
--source options to avoid ambivalent interpretation of the given
argument. For example:
mount --target /mountpoint
Listing the mounts
The listing mode is maintained for backward compatibility only.
For more robust and customizable output use findmnt(8), especially in
your scripts. Note that control characters in the mountpoint name
are replaced with '?'.
The following command lists all mounted filesystems (of type type):
mount [-l] [-t type]
The option -l adds labels to this listing. See below.
Indicating the device and filesystem
Most devices are indicated by a filename (of a block special device),
like /dev/sda1, but there are other possibilities. For example, in
the case of an NFS mount, device may look like knuth.cwi.nl:/dir. It
is also possible to indicate a block special device using its
filesystem label or UUID (see the -L and -U options below), or its
partition label or UUID. Partition identifiers are supported for
example for GUID Partition Tables (GPT).
The device name of disk partitions are unstable; hardware
reconfiguration, adding or removing a device can cause change in
names. This is reason why it's strongly recommended to use filesystem
or partition identificators like UUID or LABEL.
The command lsblk --fs provides overview of filesystems, LABELs and
UUIDs on available block devices. The command blkid -p <device>
provides details about a filesystem on the specified device.
Don't forget that there is no guarantee that UUIDs and labels are
really unique, especially if you move, share or copy the device. Use
lsblk -o +UUID,PARTUUID to verify that the UUIDs are really unique in
your system.
The recommended setup is to use tags (e.g. UUID=uuid) rather than
/dev/disk/by-{label,uuid,partuuid,partlabel} udev symlinks in the
/etc/fstab file. Tags are more readable, robust and portable. The
mount(8) command internally uses udev symlinks, so the use of
symlinks in /etc/fstab has no advantage over tags. For more details
see libblkid(3).
Note that mount(8) uses UUIDs as strings. The UUIDs from the command
line or from fstab(5) are not converted to internal binary
representation. The string representation of the UUID should be
based on lower case characters.
The proc filesystem is not associated with a special device, and when
mounting it, an arbitrary keyword, such as proc can be used instead
of a device specification. (The customary choice none is less
fortunate: the error message `none already mounted' from mount can be
confusing.)
The files /etc/fstab, /etc/mtab and /proc/mounts
The file /etc/fstab (see fstab(5)), may contain lines describing what
devices are usually mounted where, using which options. The default
location of the fstab(5) file can be overridden with the --fstab path
command-line option (see below for more details).
The command
mount -a [-t type] [-O optlist]
(usually given in a bootscript) causes all filesystems mentioned in
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 noauto keyword. Adding the -F option will make mount
fork, so that the filesystems are mounted simultaneously.
When mounting a filesystem mentioned in fstab or mtab, it suffices to
specify on the command line only the device, or only the mount point.
The programs mount and umount traditionally maintained a list of
currently mounted filesystems in the file /etc/mtab. This real mtab
file is still supported, but on current Linux systems it is better to
make it a symlink to /proc/mounts instead, because a regular mtab
file maintained in userspace cannot reliably work with namespaces,
containers and other advanced Linux features.
If no arguments are given to mount, the list of mounted filesystems
is printed.
If you want to override mount options from /etc/fstab you have to use
the -o option:
mount device|dir -o options
and then the mount options from the command line will be appended to
the list of options from /etc/fstab. The usual behavior is that the
last option wins if there are conflicting ones.
The mount program does not read the /etc/fstab file if both device
(or LABEL, UUID, PARTUUID or PARTLABEL) and dir are specified. For
example, to mount device foo at /dir:
mount /dev/foo /dir
Non-superuser mounts
Normally, only the superuser can mount filesystems. However, when
fstab contains the user option on a line, anybody can mount the
corresponding filesystem.
Thus, given a line
/dev/cdrom /cd iso9660 ro,user,noauto,unhide
any user can mount the iso9660 filesystem found on an inserted CDROM
using the command:
mount /cd
Note that mount is very strict about non-root users and all paths
specified on command line are verified before fstab is parsed or a
helper program is executed. It's strongly recommended to use a valid
mountpoint to specify filesystem, otherwise mount may fail. For
example it's bad idea to use NFS or CIFS source on command line.
For more details, see fstab(5). Only the user that mounted a
filesystem can unmount it again. If any user should be able to
unmount it, then use users instead of user in the fstab line. The
owner option is similar to the user option, with the restriction that
the user must be the owner of the special file. This may be useful
e.g. for /dev/fd if a login script makes the console user owner of
this device. The group option is similar, with the restriction that
the user must be member of the group of the special file.
Bind mounts
Remount part of the file hierarchy somewhere else. The call is:
mount --bind olddir newdir
or by using this fstab entry:
/olddir /newdir none bind
After this call the same contents are accessible in two places. One
can also remount a single file (on a single file). It's also
possible to use the bind mount to create a mountpoint from a regular
directory, for example:
mount --bind foo foo
The bind mount call attaches only (part of) a single filesystem, not
possible submounts. The entire file hierarchy including submounts is
attached a second place by using:
mount --rbind olddir newdir
Note that the filesystem mount options will remain the same as those
on the original mount point.
mount(8) since v2.27 allows to change the mount options by passing
the relevant options along with --bind. For example:
mount -o bind,ro foo foo
This feature is not supported by the Linux kernel; it is implemented
in userspace by an additional mount(2) remounting system call. This
solution is not atomic.
The alternative (classic) way to create a read-only bind mount is to
use the remount operation, for example:
mount --bind olddir newdir
mount -o remount,bind,ro olddir newdir
Note that a read-only bind will create a read-only mountpoint (VFS
entry), but the original filesystem superblock will still be
writable, meaning that the olddir will be writable, but the newdir
will be read-only.
It's also possible to change nosuid, nodev, noexec, noatime,
nodiratime and relatime VFS entry flags by "remount,bind" operation.
It's impossible to change mount options recursively (for example with
-o rbind,ro).
mount(8) since v2.31 ignores the bind flag from /etc/fstab on remount
operation (if "-o remount" specified on command line). This is
necessary to fully control mount options on remount by command line.
In the previous versions the bind flag has been always applied and it
was impossible to re-define mount options without interaction with
the bind semantic. This mount(8) behavior does not affect situations
when "remount,bind" is specified in the /etc/fstab file.
The move operation
Move a mounted tree to another place (atomically). The call is:
mount --move olddir newdir
This will cause the contents which previously appeared under olddir
to now be accessible under newdir. The physical location of the
files is not changed. Note that olddir has to be a mountpoint.
Note also that moving a mount residing under a shared mount is
invalid and unsupported. Use findmnt -o TARGET,PROPAGATION to see
the current propagation flags.
Shared subtree operations
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 the
ability to create mirrors of that mount such that mounts and unmounts
within any of the mirrors propagate to the other mirror. A slave
mount receives propagation from its master, but not vice versa. A
private mount carries no propagation abilities. An unbindable mount
is a private mount which cannot be cloned through a bind operation.
The detailed semantics are documented in
Documentation/filesystems/sharedsubtree.txt file in the kernel source
tree.
Supported operations are:
mount --make-shared mountpoint
mount --make-slave mountpoint
mount --make-private mountpoint
mount --make-unbindable mountpoint
The following commands allow one to recursively change the type of
all the mounts under a given mountpoint.
mount --make-rshared mountpoint
mount --make-rslave mountpoint
mount --make-rprivate mountpoint
mount --make-runbindable mountpoint
mount(8) does not read fstab(5) when a --make-* operation is
requested. All necessary information has to be specified on the
command line.
Note that the Linux kernel does not allow to change multiple
propagation flags with a single mount(2) system call, and the flags
cannot be mixed with other mount options and operations.
Since util-linux 2.23 the mount command allows to do more propagation
(topology) changes by one mount(8) call and do it also together with
other mount operations. This feature is EXPERIMENTAL. The
propagation flags are applied by additional mount(2) system calls
when the preceding mount operations were successful. Note that this
use case is not atomic. It is possible to specify the propagation
flags in fstab(5) as mount options (private, slave, shared,
unbindable, rprivate, rslave, rshared, runbindable).
For example:
mount --make-private --make-unbindable /dev/sda1 /foo
is the same as:
mount /dev/sda1 /foo
mount --make-private /foo
mount --make-unbindable /foo
The full set of mount options used by an invocation of mount is
determined by first extracting the mount options for the filesystem
from the fstab table, then applying any options specified by the -o
argument, and finally applying a -r or -w option, when present.
The command mount does not pass all command-line options to the
/sbin/mount.suffix mount helpers. The interface between mount and
the mount helpers is described below in the section EXTERNAL HELPERS.
Command-line options available for the mount command are:
-a, --all
Mount all filesystems (of the given types) mentioned in fstab
(except for those whose line contains the noauto keyword).
The filesystems are mounted following their order in fstab.
Note that it is a bad practice to use mount -a for fstab
checking. The recommended solution is findmnt --verify.
-B, --bind
Remount a subtree somewhere else (so that its contents are
available in both places). See above, under Bind mounts.
-c, --no-canonicalize
Don't canonicalize paths. The mount command canonicalizes all
paths (from command line or fstab) by default. This option
can be used together with the -f flag for already
canonicalized absolute paths. The option is designed for
mount helpers which call mount -i. It is strongly recommended
to not use this command-line option for normal mount
operations.
Note that mount(8) does not pass this option to the
/sbin/mount.type helpers.
-F, --fork
(Used in conjunction with -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
/usr and /usr/spool.
-f, --fake
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 -v
flag to determine what the 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 an
existing record in /etc/mtab and fails when the record already
exists (with a regular non-fake mount, this check is done by
the kernel).
-i, --internal-only
Don't call the /sbin/mount.filesystem helper even if it
exists.
-L, --label label
Mount the partition that has the specified label.
-l, --show-labels
Add the labels in the mount output. mount must have
permission to read the disk device (e.g. be set-user-ID root)
for this to work. One can set such a label for ext2, ext3 or
ext4 using the e2label(8) utility, or for XFS using
xfs_admin(8), or for reiserfs using reiserfstune(8).
-M, --move
Move a subtree to some other place. See above, the subsection
The move operation.
-n, --no-mtab
Mount without writing in /etc/mtab. This is necessary for
example when /etc is on a read-only filesystem.
-O, --test-opts opts
Limit the set of filesystems to which the -a option applies.
In this regard it is like the -t option except that -O is
useless without -a. For example, the command:
mount -a -O no_netdev
mounts all filesystems except those which have the option
_netdev specified in the options field in the /etc/fstab file.
It is different from -t in that each option is matched
exactly; a leading no at the beginning of one option does not
negate the rest.
The -t and -O options are cumulative in effect; that is, the
command
mount -a -t ext2 -O _netdev
mounts all ext2 filesystems with the _netdev option, not all
filesystems that are either ext2 or have the _netdev option
specified.
-o, --options opts
Use the specified mount options. The opts argument is a
comma-separated list. For example:
mount LABEL=mydisk -o noatime,nodev,nosuid
For more details, see the FILESYSTEM-INDEPENDENT MOUNT OPTIONS
and FILESYSTEM-SPECIFIC MOUNT OPTIONS sections.
-R, --rbind
Remount a subtree and all possible submounts somewhere else
(so that its contents are available in both places). See
above, the subsection Bind mounts.
-r, --read-only
Mount the filesystem read-only. A synonym is -o ro.
Note that, depending on the filesystem type, state and kernel
behavior, the system may still write to the device. For
example, ext3 and ext4 will replay the journal if the
filesystem is dirty. To prevent this kind of write access,
you may want to mount an ext3 or ext4 filesystem with the
ro,noload mount options or set the block device itself to
read-only mode, see the blockdev(8) command.
-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. Currently it's supported
by the mount.nfs mount helper only.
--source device
If only one argument for the mount command is given then the
argument might be interpreted as target (mountpoint) or source
(device). This option allows to explicitly define that the
argument is the mount source.
--target directory
If only one argument for the mount command is given then the
argument might be interpreted as target (mountpoint) or source
(device). This option allows to explicitly define that the
argument is the mount target.
-T, --fstab path
Specifies an alternative fstab file. If path is a directory
then the files in the directory are sorted by strverscmp(3);
files that start with "." or without an .fstab extension are
ignored. The option can be specified more than once. This
option is mostly designed for initramfs or chroot scripts
where additional configuration is specified beyond standard
system configuration.
Note that mount(8) does not pass the option --fstab to the
/sbin/mount.type helpers, meaning that the alternative fstab
files will be invisible for the helpers. This is no problem
for normal mounts, but user (non-root) mounts always require
fstab to verify the user's rights.
-t, --types fstype
The argument following the -t is used to indicate the
filesystem type. The filesystem types which are currently
supported depend on the running kernel. See /proc/filesystems
and /lib/modules/$(uname -r)/kernel/fs for a complete list of
the filesystems. The most common are ext2, ext3, ext4, xfs,
btrfs, vfat, sysfs, proc, nfs and cifs.
The programs mount and umount support filesystem subtypes.
The subtype is defined by a '.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 deprecated).
If no -t option is given, or if the auto type is specified,
mount will try to guess the desired type. Mount uses the
blkid library for guessing the filesystem type; if that does
not turn up anything that looks familiar, mount will try to
read the file /etc/filesystems, or, if that does not exist,
/proc/filesystems. All of the filesystem types listed there
will be tried, except for those that are labeled "nodev" (e.g.
devpts, proc and nfs). If /etc/filesystems ends in a line
with a single *, mount will read /proc/filesystems afterwards.
While trying, all filesystem types will be mounted with the
mount option silent.
The auto type may be useful for user-mounted floppies.
Creating a file /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.
More than one type may be specified in a comma-separated list,
for option -t as well as in an /etc/fstab entry. The list of
filesystem types for option -t can be prefixed with no to
specify the filesystem types on which no action should be
taken. The prefix no has no effect when specified in an
/etc/fstab entry.
The prefix no can be meaningful with the -a option. For
example, the command
mount -a -t nomsdos,smbfs
mounts all filesystems except those of type msdos and smbfs.
For most types all the mount program has to do is issue a
simple 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) an 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
/sbin/mount.type (if that exists) when called with type type.
Since different versions of the smbmount program have
different calling conventions, /sbin/mount.smbfs may have to
be a shell script that sets up the desired call.
-U, --uuid uuid
Mount the partition that has the specified uuid.
-v, --verbose
Verbose mode.
-w, --rw, --read-write
Mount the filesystem read/write. The read-write is kernel
default. A synonym is -o rw.
Note that specify -w on command line forces mount command to
never try read-only mount on write-protected devices. The
default is try read-only if the previous mount syscall with
read-write flags failed.
-V, --version
Display version information and exit.
-h, --help
Display help text and exit.
Some of these options are only useful when they appear in the
/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. Note that filesystems also have per-filesystem
specific default mount options (see for example tune2fs -l output for
extN filesystems).
The following options apply to any filesystem that is being mounted
(but not every filesystem actually honors them – e.g., the sync
option today has an effect only for ext2, ext3, fat, vfat and ufs):
async All I/O to the filesystem should be done asynchronously. (See
also the sync option.)
atime Do not use the noatime feature, so the inode access time is
controlled by kernel defaults. See also the descriptions of
the relatime and strictatime mount options.
noatime
Do not update inode access times on this filesystem (e.g. for
faster access on the news spool to speed up news servers).
This works for all inode types (directories too), so it
implies nodiratime.
auto Can be mounted with the -a option.
noauto Can only be mounted explicitly (i.e., the -a option will not
cause the filesystem to be mounted).
context=context, fscontext=context, defcontext=context, and
rootcontext=context
The 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 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
context="system_u:object_r:removable_t".
Two other options are fscontext= and 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 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 defcontext= option. This overrides the value set for
unlabeled files in the policy and requires a filesystem that
supports xattr labeling.
The rootcontext= option allows you to explicitly label the
root inode of a FS being mounted before that FS or inode
becomes visible to userspace. This was found to be useful for
things like stateless linux.
Note that the kernel rejects any remount request that includes
the context option, even when unchanged from the current
context.
Warning: the context value might contain commas, in which case
the value has to be properly quoted, otherwise mount(8) will
interpret the comma as a separator between mount options.
Don't forget that the shell strips off quotes and thus double
quoting is required. For example:
mount -t tmpfs none /mnt -o \
'context="system_u:object_r:tmp_t:s0:c127,c456",noexec'
For more details, see selinux(8).
defaults
Use the default options: rw, suid, dev, exec, auto, nouser,
and async.
Note that the real set of all default mount options depends on
kernel and filesystem type. See the beginning of this section
for more details.
dev Interpret character or block special devices on the
filesystem.
nodev Do not interpret character or block special devices on the
file system.
diratime
Update directory inode access times on this filesystem. This
is the default. (This option is ignored when noatime is set.)
nodiratime
Do not update directory inode access times on this filesystem.
(This option is implied when noatime is set.)
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.
exec Permit execution of binaries.
noexec Do not permit direct execution of any binaries on the mounted
filesystem.
group Allow an ordinary user to mount the filesystem if one of that
user's groups matches the group of the device. This option
implies the options nosuid and nodev (unless overridden by
subsequent options, as in the option line group,dev,suid).
iversion
Every time the inode is modified, the i_version field will be
incremented.
noiversion
Do not increment the i_version inode field.
mand Allow mandatory locks on this filesystem. See fcntl(2).
nomand Do not allow mandatory locks on this filesystem.
_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).
nofail Do not report errors for this device if it does not exist.
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 it doesn't break mutt or other applications that
need to know if a file has been read since the last time it
was modified.)
Since Linux 2.6.30, the kernel defaults to the behavior
provided by this option (unless noatime was specified), and
the strictatime option is required to obtain traditional
semantics. In addition, since Linux 2.6.30, the file's last
access time is always updated if it is more than 1 day old.
norelatime
Do not use the relatime feature. See also the strictatime
mount option.
strictatime
Allows to explicitly request full atime updates. This makes
it possible for the kernel to default to relatime or noatime
but still allow userspace to override it. For more details
about the default system mount options see /proc/mounts.
nostrictatime
Use the kernel's default behavior for inode access time
updates.
lazytime
Only update times (atime, mtime, ctime) on the in-memory
version of the file inode.
This mount option significantly reduces writes to the inode
table for workloads that perform frequent random writes to
preallocated files.
The on-disk timestamps are updated only when:
- the inode needs to be updated for some change unrelated to
file timestamps
- the application employs fsync(2), syncfs(2), or sync(2)
- an undeleted inode is evicted from memory
- more than 24 hours have passed since the i-node was written
to disk.
nolazytime
Do not use the lazytime feature.
suid Allow set-user-ID or set-group-ID bits to take effect.
nosuid Do not allow set-user-ID or set-group-ID bits to take effect.
silent Turn on the silent flag.
loud Turn off the silent flag.
owner Allow an ordinary user to mount the filesystem if that user is
the owner of the device. This option implies the options
nosuid and nodev (unless overridden by subsequent options, as
in the option line owner,dev,suid).
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 writable. It does
not change device or mount point.
The remount operation together with the bind flag has special
semantic. See above, the subsection Bind mounts.
The remount functionality follows the standard way the mount
command works with options from fstab. This means that mount
does not read fstab (or mtab) only when both device and dir
are specified.
mount -o remount,rw /dev/foo /dir
After this call all old mount options are replaced and
arbitrary stuff from fstab (or mtab) is ignored, except the
loop= option which is internally generated and maintained by
the mount command.
mount -o remount,rw /dir
After this call, mount reads fstab and merges these options
with the options from the command line (-o). If no mountpoint
is found in fstab, then a remount with unspecified source is
allowed.
ro Mount the filesystem read-only.
rw Mount the filesystem read-write.
sync All I/O to the filesystem should be done synchronously. In
the case of media with a limited number of write cycles (e.g.
some flash drives), sync may cause life-cycle shortening.
user Allow an ordinary user to mount the filesystem. The name of
the mounting user is written to the mtab file (or to the
private libmount file in /run/mount on systems without a
regular mtab) so that this same user can unmount the
filesystem again. This option implies the options noexec,
nosuid, and nodev (unless overridden by subsequent options, as
in the option line user,exec,dev,suid).
nouser Forbid an ordinary user to mount the filesystem. This is the
default; it does not imply any other options.
users Allow any user to mount and to unmount the filesystem, even
when some other ordinary user mounted it. This option implies
the options noexec, nosuid, and nodev (unless overridden by
subsequent options, as in the option line
users,exec,dev,suid).
X-* All options prefixed with "X-" are interpreted as comments or
as userspace application-specific options. These options are
not stored in the user space (e.g. mtab file), nor sent to the
mount.type helpers nor to the mount(2) system call. The
suggested format is X-appname.option.
x-* The same as X-* options, but stored permanently in the user
space. It means the options are also available for umount or
another operations. Note that maintain mount options in user
space is tricky, because it's necessary use libmount based
tools and there is no guarantee that the options will be
always available (for example after a move mount operation or
in unshared namespace).
Note that before util-linux v2.30 the x-* options have not
been maintained by libmount and stored in user space
(functionality was the same as have X-* now), but due to
growing number of use-cases (in initrd, systemd etc.) the
functionality have been extended to keep existing fstab
configurations usable without a change.
X-mount.mkdir[=mode]
Allow to make a target directory (mountpoint). The optional
argument mode specifies the filesystem access mode used for
mkdir(2) in octal notation. The default mode is 0755. This
functionality is supported only for root users. The option is
also supported as x-mount.mkdir, this notation is deprecated
for mount.mkdir since v2.30.
You should consult the respective man page for the filesystem first.
If you want to know what options the ext4 filesystem supports, then
check the ext4(5) man page. If that doesn't exist, you can also
check the corresponding mount page like mount.cifs(8). Note that you
might have to install the respective userland tools.
The following options apply only to certain filesystems. We sort
them by filesystem. They all follow the -o flag.
What options are supported depends a bit on the running kernel. More
info may be found in the kernel source subdirectory
Documentation/filesystems.
Mount options for adfs
uid=value and gid=value
Set the owner and group of the files in the filesystem
(default: uid=gid=0).
ownmask=value and othmask=value
Set the permission mask for ADFS 'owner' permissions and
'other' permissions, respectively (default: 0700 and 0077,
respectively). See also
/usr/src/linux/Documentation/filesystems/adfs.txt.
Mount options for affs
uid=value and gid=value
Set the owner and group of the root of the filesystem
(default: uid=gid=0, but with option uid or gid without
specified value, the UID and GID of the current process are
taken).
setuid=value and setgid=value
Set the owner and group of all files.
mode=value
Set the mode of all files to value & 0777 disregarding the
original permissions. Add search permission to directories
that have read permission. The value is given in octal.
protect
Do not allow any changes to the protection bits on the
filesystem.
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...
verbose
Print an informational message for each successful mount.
prefix=string
Prefix used before volume name, when following a link.
volume=string
Prefix (of length at most 30) used before '/' when following a
symbolic link.
reserved=value
(Default: 2.) Number of unused blocks at the start of the
device.
root=value
Give explicitly the location of the root block.
bs=value
Give blocksize. Allowed values are 512, 1024, 2048, 4096.
grpquota|noquota|quota|usrquota
These options are accepted but ignored. (However, quota
utilities may react to such strings in /etc/fstab.)
Mount options for debugfs
The debugfs filesystem is a pseudo filesystem, traditionally mounted
on /sys/kernel/debug. As of kernel version 3.4, debugfs has the
following options:
uid=n, gid=n
Set the owner and group of the mountpoint.
mode=value
Sets the mode of the mountpoint.
Mount options for devpts
The devpts filesystem is a pseudo filesystem, traditionally mounted
on /dev/pts. In order to acquire a pseudo terminal, a process opens
/dev/ptmx; the number of the pseudo terminal is then made available
to the process and the pseudo terminal slave can be accessed as
/dev/pts/<number>.
uid=value and gid=value
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 gid=5 will cause newly
created PTYs to belong to the tty group.
mode=value
Set the mode of newly created PTYs to the specified value.
The default is 0600. A value of mode=620 and gid=5 makes
"mesg y" the default on newly created PTYs.
newinstance
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 newinstance option share the
same set of pty indices (i.e legacy mode). Each mount of
devpts with the 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, /dev/ptmx must be a symbolic
link to pts/ptmx. See Documentation/filesystems/devpts.txt in
the linux kernel source tree for details.
ptmxmode=value
Set the mode for the new ptmx device node in the devpts
filesystem.
With the support for multiple instances of devpts (see
newinstance option above), each instance has a private ptmx
node in the root of the devpts filesystem (typically
/dev/pts/ptmx).
For compatibility with older versions of the kernel, the
default mode of the new ptmx node is 0000. ptmxmode=value
specifies a more useful mode for the ptmx node and is highly
recommended when the 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.
Mount options for fat
(Note: fat is not a separate filesystem, but a common part of the
msdos, umsdos and vfat filesystems.)
blocksize={512|1024|2048}
Set blocksize (default 512). This option is obsolete.
uid=value and gid=value
Set the owner and group of all files. (Default: the UID and
GID of the current process.)
umask=value
Set the umask (the bitmask of the permissions that are not
present). The default is the umask of the current process.
The value is given in octal.
dmask=value
Set the umask applied to directories only. The default is the
umask of the current process. The value is given in octal.
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.
allow_utime=value
This option controls the permission check of mtime/atime.
20 If current process is in group of file's group ID, you
can change timestamp.
2 Other users can change timestamp.
The default is set from `dmask' option. (If the directory is
writable, utime(2) is also allowed. I.e. ~dmask & 022)
Normally 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 inflexible. With
this option you can relax it.
check=value
Three different levels of pickyness can be chosen:
r[elaxed]
Upper and lower case are accepted and equivalent, long
name parts are truncated (e.g. verylongname.foobar
becomes verylong.foo), leading and embedded spaces are
accepted in each name part (name and extension).
n[ormal]
Like "relaxed", but many special characters (*, ?, <,
spaces, etc.) are rejected. This is the default.
s[trict]
Like "normal", but names that contain long parts or
special characters that are sometimes used on Linux but
are not accepted by MS-DOS (+, =, etc.) are rejected.
codepage=value
Sets the codepage for converting to shortname characters on
FAT and VFAT filesystems. By default, codepage 437 is used.
conv=mode
This option is obsolete and may fail or being ignored.
cvf_format=module
Forces the driver to use the CVF (Compressed Volume File)
module 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.
cvf_option=option
Option passed to the CVF module. This option is obsolete.
debug Turn on the 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).
discard
If set, causes discard/TRIM commands to be issued to the block
device when blocks are freed. This is useful for SSD devices
and sparse/thinly-provisioned LUNs.
dos1xfloppy
If set, use a fallback default BIOS Parameter Block
configuration, determined by backing device size. These
static parameters match defaults assumed by DOS 1.x for 160
kiB, 180 kiB, 320 kiB, and 360 kiB floppies and floppy images.
errors={panic|continue|remount-ro}
Specify FAT behavior on critical errors: panic, continue
without doing anything, or remount the partition in read-only
mode (default behavior).
fat={12|16|32}
Specify a 12, 16 or 32 bit fat. This overrides the automatic
FAT type detection routine. Use with caution!
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.
nfs={stale_rw|nostale_ro}
Enable this only if you want to export the FAT filesystem over
NFS.
stale_rw: This option maintains an index (cache) of directory
inodes which is used by the nfs-related code to improve look-
ups. Full file operations (read/write) over NFS are supported
but with cache eviction at NFS server, this could result in
spurious ESTALE errors.
nostale_ro: This option bases the inode number and file handle
on the on-disk location of a file in the FAT directory entry.
This ensures that ESTALE will not be returned after a file is
evicted from the inode cache. However, it means that
operations such as rename, create and unlink could cause file
handles that previously pointed at one file to point at a
different file, potentially causing data corruption. For this
reason, this option also mounts the filesystem readonly.
To maintain backward compatibility, '-o nfs' is also accepted,
defaulting to stale_rw.
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.
time_offset=minutes
Set offset for conversion of timestamps from local time used
by FAT to UTC. I.e., minutes will be subtracted from each
timestamp to convert it to UTC used internally by Linux. This
is useful when the time zone set in the kernel via
settimeofday(2) is not the time zone used by the filesystem.
Note that this option still does not provide correct time
stamps in all cases in presence of DST - time stamps in a
different DST setting will be off by one hour.
quiet Turn on the quiet flag. Attempts to chown or chmod files do
not return errors, although they fail. Use with caution!
rodir FAT has the ATTR_RO (read-only) attribute. On Windows, the
ATTR_RO of the directory will just be ignored, and is used
only by applications as a flag (e.g. it's set for the
customized folder).
If you want to use ATTR_RO as read-only flag even for the
directory, set this option.
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.
sys_immutable
If set, ATTR_SYS attribute on FAT is handled as IMMUTABLE flag
on Linux. Not set by default.
flush If set, the filesystem will try to flush to disk more early
than normal. Not set by default.
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.
dots, nodots, dotsOK=[yes|no]
Various misguided attempts to force Unix or DOS conventions
onto a FAT filesystem.
Mount options for hfs
creator=cccc, type=cccc
Set the creator/type values as shown by the MacOS finder used
for creating new files. Default values: '????'.
uid=n, gid=n
Set the owner and group of all files. (Default: the UID and
GID of the current process.)
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.
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.
part=n Select partition number n from the device. Only makes sense
for CDROMs. Defaults to not parsing the partition table at
all.
quiet Don't complain about invalid mount options.
Mount options for hpfs
uid=value and gid=value
Set the owner and group of all files. (Default: the UID and
GID of the current process.)
umask=value
Set the umask (the bitmask of the permissions that are not
present). The default is the umask of the current process.
The value is given in octal.
case={lower|asis}
Convert all files names to lower case, or leave them.
(Default: case=lower.)
conv=mode
This option is obsolete and may fail or being ignored.
nocheck
Do not abort mounting when certain consistency checks fail.
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 udf filesystem.)
Normal 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).
norock Disable the use of Rock Ridge extensions, even if available.
Cf. map.
nojoliet
Disable the use of Microsoft Joliet extensions, even if
available. Cf. map.
check={r[elaxed]|s[trict]}
With check=relaxed, a filename is first converted to lower
case before doing the lookup. This is probably only
meaningful together with norock and map=normal. (Default:
check=strict.)
uid=value and gid=value
Give all files in the filesystem the indicated user or group
id, possibly overriding the information found in the Rock
Ridge extensions. (Default: uid=0,gid=0.)
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 map=off no name translation is done. See
norock. (Default: map=normal.) map=acorn is like map=normal
but also apply Acorn extensions if present.
mode=value
For non-Rock Ridge volumes, give all files the indicated mode.
(Default: read and execute permission for everybody.) Octal
mode values require a leading 0.
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.)
block={512|1024|2048}
Set the block size to the indicated value. (Default:
block=1024.)
conv=mode
This option is obsolete and may fail or being ignored.
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
16 MB.
session=x
Select number of session on multisession CD.
sbsector=xxx
Session begins from sector xxx.
The following options are the same as for vfat and specifying them
only makes sense when using discs encoded using Microsoft's Joliet
extensions.
iocharset=value
Character set to use for converting 16 bit Unicode characters
on CD to 8 bit characters. The default is iso8859-1.
utf8 Convert 16 bit Unicode characters on CD to UTF-8.
Mount options for jfs
iocharset=name
Character set to use for converting from Unicode to ASCII.
The default is to do no conversion. Use iocharset=utf8 for
UTF8 translations. This requires CONFIG_NLS_UTF8 to be set in
the kernel .config file.
resize=value
Resize the volume to 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 resize
keyword with no value will grow the volume to the full size of
the partition.
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 ends.
integrity
Default. Commit metadata changes to the journal. Use this
option to remount a volume where the nointegrity option was
previously specified in order to restore normal behavior.
errors={continue|remount-ro|panic}
Define the behavior 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.)
noquota|quota|usrquota|grpquota
These options are accepted but ignored.
Mount options for msdos
See mount options for fat. If the msdos filesystem detects an
inconsistency, it reports an error and sets the file system read-
only. The filesystem can be made writable again by remounting it.
Mount options for ncpfs
Just like nfs, the ncpfs implementation expects a binary argument (a
struct ncp_mount_data) to the mount system call. This argument is
constructed by ncpmount(8) and the current version of mount (2.12)
does not know anything about ncpfs.
Mount options for ntfs
iocharset=name
Character set to use when returning file names. Unlike VFAT,
NTFS suppresses names that contain nonconvertible characters.
Deprecated.
nls=name
New name for the option earlier called iocharset.
utf8 Use UTF-8 for converting file names.
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.
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.
uid=value, gid=value and umask=value
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.
Mount options for overlay
Since Linux 3.18 the overlay pseudo filesystem implements a union
mount for other filesystems.
An overlay filesystem combines two filesystems - an upper filesystem
and a lower filesystem. When a name exists in both filesystems, the
object in the upper filesystem is visible while the object in the
lower filesystem is either hidden or, in the case of directories,
merged with the upper object.
The lower filesystem can be any filesystem supported by Linux and
does not need to be writable. The lower filesystem can even be
another overlayfs. The upper filesystem will normally be writable
and if it is it must support the creation of trusted.* extended
attributes, and must provide a valid d_type in readdir responses, so
NFS is not suitable.
A read-only overlay of two read-only filesystems may use any
filesystem type. The options lowerdir and upperdir are combined into
a merged directory by using:
mount -t overlay overlay \
-olowerdir=/lower,upperdir=/upper,workdir=/work /merged
lowerdir=directory
Any filesystem, does not need to be on a writable filesystem.
upperdir=directory
The upperdir is normally on a writable filesystem.
workdir=directory
The workdir needs to be an empty directory on the same
filesystem as upperdir.
Mount options for reiserfs
Reiserfs is a journaling filesystem.
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.
hash={rupasov|tea|r5|detect}
Choose which hash function reiserfs will use to find files
within directories.
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.
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.
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.
detect Instructs 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.
hashed_relocation
Tunes the block allocator. This may provide performance
improvements in some situations.
no_unhashed_relocation
Tunes the block allocator. This may provide performance
improvements in some situations.
noborder
Disable the border allocator algorithm invented by Yury Yu.
Rupasov. This may provide performance improvements in some
situations.
nolog Disable journaling. 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 journaling operations,
save for actual writes into its journaling area.
Implementation of nolog is a work in progress.
notail By default, reiserfs stores small files and `file tails'
directly into its tree. This confuses some utilities such as
LILO(8). This option is used to disable packing of files into
the tree.
replayonly
Replay the transactions which are in the journal, but do not
actually mount the filesystem. Mainly used by reiserfsck.
resize=number
A remount option which permits online expansion of reiserfs
partitions. Instructs reiserfs to assume that the device has
number blocks. This option is designed for use with devices
which are under logical volume management (LVM). There is a
special resizer utility which can be obtained from
ftp://ftp.namesys.com/pub/reiserfsprogs.
user_xattr
Enable Extended User Attributes. See the attr(5) manual page.
acl Enable POSIX Access Control Lists. See the acl(5) manual
page.
barrier=none / barrier=flush
This disables / enables the use of write barriers in the
journaling code. barrier=none disables, barrier=flush enables
(default). This also requires an IO stack which can support
barriers, and if reiserfs gets an error on a barrier write, it
will disable barriers 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.
Mount options for ubifs
UBIFS is a flash filesystem which works on top of UBI volumes. Note
that atime is not supported and is always turned off.
The device name may be specified as
ubiX_Y UBI device number X, volume number Y
ubiY UBI device number 0, volume number Y
ubiX:NAME
UBI device number X, volume with name NAME
ubi:NAME
UBI device number 0, volume with name NAME
Alternative ! separator may be used instead of :.
The following mount options are available:
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.
no_bulk_read
Do not bulk-read. This is the default.
chk_data_crc
Check data CRC-32 checksums. This is the default.
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.
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 none option.
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 iso9660.
gid= Set the default group.
umask= Set the default umask. The value is given in octal.
uid= Set the default user.
unhide Show otherwise hidden files.
undelete
Show deleted files in lists.
nostrict
Unset strict conformance.
iocharset
Set the NLS character set.
bs= Set the block size. (May not work unless 2048.)
novrs Skip volume sequence recognition.
session=
Set the CDROM session counting from 0. Default: last session.
anchor=
Override standard anchor location. Default: 256.
volume=
Override the VolumeDesc location. (unused)
partition=
Override the PartitionDesc location. (unused)
lastblock=
Set the last block of the filesystem.
fileset=
Override the fileset block location. (unused)
rootdir=
Override the root directory location. (unused)
Mount options for ufs
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:
old Old format of ufs, this is the default, read only.
(Don't forget to give the -r option.)
44bsd For filesystems created by a BSD-like system (NetBSD,
FreeBSD, OpenBSD).
ufs2 Used in FreeBSD 5.x supported as read-write.
5xbsd Synonym for ufs2.
sun For filesystems created by SunOS or Solaris on Sparc.
sunx86 For filesystems created by Solaris on x86.
hp For filesystems created by HP-UX, read-only.
nextstep
For filesystems created by NeXTStep (on NeXT station)
(currently read only).
nextstep-cd
For NextStep CDROMs (block_size == 2048), read-only.
openstep
For filesystems created by OpenStep (currently read
only). The same filesystem type is also used by Mac OS
X.
onerror=value
Set behavior on error:
panic If an error is encountered, cause a kernel panic.
[lock|umount|repair]
These mount options don't do anything at present; when
an error is encountered only a console message is
printed.
Mount options for umsdos
See mount options for msdos. The dotsOK option is explicitly killed
by umsdos.
Mount options for vfat
First of all, the mount options for fat are recognized. The dotsOK
option is explicitly killed by vfat. Furthermore, there are
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 invalid on the vfat
filesystem. The escape sequence that gets used, where u is
the Unicode character, is: ':', (u & 0x3f), ((u>>6) & 0x3f),
(u>>12).
posix Allow two files with names that only differ in case. This
option is obsolete.
nonumtail
First try to make a short name without sequence number, before
trying name~num.ext.
utf8 UTF8 is the filesystem safe 8-bit encoding of Unicode that is
used by the console. It can 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.
shortname=mode
Defines the behavior for creation and display of filenames
which fit into 8.3 characters. If a long name for a file
exists, it will always be the preferred one for display.
There are four modes:
lower Force the short name to lower case upon display; store
a long name when the short name is not all upper case.
win95 Force the short name to upper case upon display; store
a long name when the short name is not all upper case.
winnt Display the short name as is; store a long name when
the short name is not all lower case or all upper case.
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.
Mount options for usbfs
devuid=uid and devgid=gid and devmode=mode
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.
busuid=uid and busgid=gid and busmode=mode
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.
listuid=uid and listgid=gid and listmode=mode
Set the owner and group and mode of the file devices (default:
uid=gid=0, mode=0444). The mode is given in octal.
One further possible type is a mount via the loop device. For
example, the command
mount /tmp/disk.img /mnt -t vfat -o loop=/dev/loop3
will set up the loop device /dev/loop3 to correspond to the file
/tmp/disk.img, and then mount this device on /mnt.
If no explicit loop device is mentioned (but just an option `-o loop'
is given), then mount will try to find some unused loop device and
use that, for example
mount /tmp/disk.img /mnt -o loop
The mount command 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:
mount /tmp/disk.img /mnt
mount -t ext3 /tmp/disk.img /mnt
This type of mount knows about three options, namely loop, offset and
sizelimit, that are really options to losetup(8). (These options can
be used in addition to those specific to the filesystem type.)
Since Linux 2.6.25 auto-destruction of loop devices is supported,
meaning that any loop device allocated by mount will be freed by
umount independently of /etc/mtab.
You can also free a loop device by hand, using losetup -d or umount
-d.
Since util-linux v2.29 mount command re-uses the loop device rather
than initialize a new device if the same backing file is already used
for some loop device with the same offset and sizelimit. This is
necessary to avoid a filesystem corruption.
mount has the following return codes (the bits can be ORed):
0 success
1 incorrect invocation or permissions
2 system error (out of memory, cannot fork, no more loop
devices)
4 internal mount bug
8 user interrupt
16 problems writing or locking /etc/mtab
32 mount failure
64 some mount succeeded
The command mount -a returns 0 (all succeeded), 32 (all failed), or
64 (some failed, some succeeded).
The syntax of external mount helpers is:
/sbin/mount.suffix spec dir [-sfnv] [-o options] [-t
type.subtype]
where the suffix is the filesystem type and the -sfnvo options have
the same meaning as the normal mount options. The -t option is used
for filesystems with subtypes support (for example /sbin/mount.fuse
-t fuse.sshfs).
The command mount does not pass the mount options unbindable,
runbindable, private, rprivate, slave, rslave, shared, rshared, auto,
noauto, comment, x-*, loop, offset and sizelimit to the
mount.<suffix> helpers. All other options are used in a comma-
separated list as argument to the -o option.
/etc/fstab filesystem table
/etc/mtab table of mounted filesystems
/etc/mtab~ lock file
/etc/mtab.tmp temporary file
/etc/filesystems a list of filesystem types to try
LIBMOUNT_FSTAB=<path>
overrides the default location of the fstab file (ignored for
suid)
LIBMOUNT_MTAB=<path>
overrides the default location of the mtab file (ignored for
suid)
LIBMOUNT_DEBUG=all
enables libmount debug output
LIBBLKID_DEBUG=all
enables libblkid debug output
LOOPDEV_DEBUG=all
enables loop device setup debug output
mount(2), umount(2), umount(8), fstab(5), nfs(5), xfs(5), e2label(8),
findmnt(8), losetup(8), mke2fs(8), mountd(8), nfsd(8), swapon(8),
tune2fs(8), xfs_admin(8)
It is possible for a corrupted filesystem to cause a crash.
Some Linux filesystems don't support -o sync nor -o dirsync (the
ext2, ext3, fat and vfat filesystems do support synchronous updates
(a la BSD) when mounted with the sync option).
The -o remount may not be able to change mount parameters (all
ext2fs-specific parameters, except sb, are changeable with a remount,
for example, but you can't change gid or umask for the fatfs).
It is possible that the files /etc/mtab and /proc/mounts don't match
on systems with a regular mtab file. 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. on a remote NFS
server -- in certain cases the mount command may report unreliable
information about an NFS mount point and the /proc/mounts file
usually contains more reliable information.) This is another reason
to replace the mtab file with a symlink to the /proc/mounts file.
Checking files on NFS filesystems referenced by file descriptors
(i.e. the fcntl and ioctl families of functions) may lead to
inconsistent results due to the lack of a consistency check in the
kernel even if noac is used.
The loop option with the offset or sizelimit options used may fail
when using older kernels if the mount command can't confirm that the
size of the block device has been configured as requested. This
situation can be worked around by using the losetup command manually
before calling mount with the configured loop device.
A mount command existed in Version 5 AT&T UNIX.
Karel Zak <kzak@redhat.com>
The mount command is part of the util-linux package and is available
from https://www.kernel.org/pub/linux/utils/util-linux/.
This page is part of the util-linux (a random collection of Linux
utilities) project. Information about the project can be found at
⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩. If you have a
bug report for this manual page, send it to
util-linux@vger.kernel.org. This page was obtained from the
project's upstream Git repository
⟨git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git⟩ on
2018-02-02. (At that time, the date of the most recent commit that
was found in the repository was 2018-02-01.) If you discover any
rendering problems in this HTML version of the page, or you believe
there is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
util-linux August 2015 MOUNT(8)
Pages that refer to this page: eject(1), fusermount3(1), mountpoint(1), quotasync(1), systemd-mount(1), unshare(1), chown(2), fcntl(2), fsync(2), ioctl_iflags(2), mount(2), open(2), open_by_handle_at(2), umount(2), getmntent(3), getsubopt(3), fd(4), hd(4), loop(4), ram(4), autofs(5), ext4(5), filesystems(5), fstab(5), lxc.container.conf(5), namespace.conf(5), nfs(5), nfsmount.conf(5), proc(5), systemd.automount(5), systemd.mount(5), tmpfs(5), xfs(5), bootparam(7), fanotify(7), hier(7), inode(7), man-pages(7), automount(8), btrfs-subvolume(8), e4crypt(8), e4defrag(8), findmnt(8), fsck.cramfs(8), fsck.xfs(8), fsfreeze(8), fstrim(8), lsof(8), mkfs.cramfs(8), mkfs.xfs(8), mount(8), mount.fuse(8), mount.nfs(8), pam_namespace(8), pivot_root(8), quotaon(8), swapon(8), switch_root(8), systemd-remount-fs.service(8), tune2fs(8), umount(8), xfs_admin(8), xfs_db(8), xfs_freeze(8), xfs_growfs(8), xfs_logprint(8), xfs_rtcp(8)
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