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MOUNT(8) System Administration MOUNT(8)
mount - mount a filesystem
mount [-h|-V]
mount [-l] [-t fstype]
mount -a [-fFnrsvw] [-t fstype] [-O optlist]
mount [-fnrsvw] [-o options] device|mountpoint
mount [-fnrsvw] [-t fstype] [-o options] device mountpoint
mount --bind|--rbind|--move olddir newdir
mount
--make-[shared|slave|private|unbindable|rshared|rslave|rprivate|runbindable]
mountpoint
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 other 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 ambiguous interpretation of the
given argument. For example:
mount --target /mountpoint
The same filesystem may be mounted more than once, and in some
cases (e.g., network filesystems) the same filesystem may be
mounted on the same mountpoint multiple times. The mount command
does not implement any policy to control this behavior. All
behavior is controlled by the kernel and it is usually specific
to the filesystem driver. The exception is --all, in this case
already mounted filesystems are ignored (see --all below for more
details).
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.
The device names of disk partitions are unstable; hardware
reconfiguration, and adding or removing a device can cause
changes in names. This is the reason why it’s strongly
recommended to use filesystem or partition identifiers like UUID
or LABEL. Currently supported identifiers (tags):
LABEL=label
Human readable filesystem identifier. See also -L.
UUID=uuid
Filesystem universally unique identifier. The format of the
UUID is usually a series of hex digits separated by hyphens.
See also -U.
Note that mount 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.
PARTLABEL=label
Human readable partition identifier. This identifier is
independent on filesystem and does not change by mkfs or
mkswap operations. It’s supported for example for GUID
Partition Tables (GPT).
PARTUUID=uuid
Partition universally unique identifier. This identifier is
independent on filesystem and does not change by mkfs or
mkswap operations. It’s supported for example for GUID
Partition Tables (GPT).
ID=id
Hardware block device ID as generated by udevd. This
identifier is usually based on WWN (unique storage
identifier) and assigned by the hardware manufacturer. See ls
/dev/disk/by-id for more details, this directory and running
udevd is required. This identifier is not recommended for
generic use as the identifier is not strictly defined and it
depends on udev, udev rules and hardware.
The command lsblk --fs provides an 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,id,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).
The proc filesystem is not associated with a special device, and
when mounting it, an arbitrary keyword - for example, 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 in parallel.
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(8) traditionally maintained a list
of currently mounted filesystems in the file /etc/mtab. The
support for regular classic /etc/mtab is completely disabled at
compile time by default, because on current Linux systems it is
better to make /etc/mtab a symlink to /proc/mounts instead. The
regular mtab file maintained in userspace cannot reliably work
with namespaces, containers and other advanced Linux features. If
the regular mtab support is enabled, then it’s possible to use
the file as well as the symlink.
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. This default behaviour
can be changed using the --options-mode command-line option. 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, ID, PARTUUID or PARTLABEL) and dir are
specified. For example, to mount device foo at /dir:
mount /dev/foo /dir
This default behaviour can be changed by using the
--options-source-force command-line option to always read
configuration from fstab. For non-root users mount always reads
the fstab configuration.
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 a bad idea to use NFS or CIFS source on command
line.
Since util-linux 2.35, mount does not exit when user permissions
are inadequate according to libmount’s internal security rules.
Instead, it drops suid permissions and continues as regular
non-root user. This behavior supports use-cases where root
permissions are not necessary (e.g., fuse filesystems, user
namespaces, etc).
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 a member of the group of the
special file.
The user mount option is accepted if no username is specified. If
used in the format user=someone, the option is silently ignored
and visible only for external mount helpers (/sbin/mount.<type>)
for compatibility with some network filesystems.
Bind mount operation
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.
It is important to understand that "bind" does not create any
second-class or special node in the kernel VFS. The "bind" is
just another operation to attach a filesystem. There is nowhere
stored information that the filesystem has been attached by a
"bind" operation. The olddir and newdir are independent and the
olddir may be unmounted.
One can also remount a single file (on a single file). It’s also
possible to use a 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 can be attached a second place by using:
mount --rbind olddir newdir
Note that the filesystem mount options maintained by the kernel
will remain the same as those on the original mount point. The
userspace mount options (e.g., _netdev) will not be copied by
mount and it’s necessary to explicitly specify the options on the
mount command line.
Since util-linux 2.27 mount permits changing 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, relatime and nosymfollow VFS entry flags via a
"remount,bind" operation. The other flags (for example
filesystem-specific flags) are silently ignored. The classic
mount(2) system call does not allow to change mount options
recursively (for example with -o rbind,ro). The recursive
semantic is possible with a new mount_setattr(2) kernel system
call and it’s supported since libmount from util-linux v2.39 by a
new experimental "recursive" option argument (e.g. -o
rbind,ro=recursive). For more details see the
FILESYSTEM-INDEPENDENT MOUNT OPTIONS section.
Since util-linux 2.31, mount ignores the bind flag from
/etc/fstab on a remount operation (if -o remount is specified on
command line). This is necessary to fully control mount options
on remount by command line. In 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
behavior does not affect situations when "remount,bind" is
specified in the /etc/fstab file.
Since util-linux 2.39, mount may use the new kernel mount API if
it is available. This new kernel interface provides a more
precise way to work with mountpoint attributes. For example, the
-o bind,rw operation will create a read-write node even if the
original node was read-only. This was impossible with the old
classic mount(2) syscall, where the read-only VFS flag was
inherited from the original node.
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; see also mount_namespaces(7).
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 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 changing 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 can be used to do more
propagation (topology) changes by one mount(8) call and do it
also together with other mount operations. 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 mount command 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 EXTERNAL HELPERS
section.
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.
The mount command compares filesystem source, target (and fs
root for bind mount or btrfs) to detect already mounted
filesystems. The kernel table with already mounted
filesystems is cached during mount --all. This means that all
duplicated fstab entries will be mounted.
The correct functionality depends on /proc (to detect already
mounted filesystems) and on /sys (to evaluate filesystem tags
like UUID= or LABEL=). It’s strongly recommended to mount
/proc and /sys filesystems before mount -a is executed, or
keep /proc and /sys at the beginning of fstab.
The option --all is possible to use for remount operation
too. In this case all filters (-t and -O) are applied to the
table of already mounted filesystems.
Since version 2.35 it is possible to use the command line
option -o to alter mount options from fstab (see also
--options-mode).
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 mount
operation.
-c, --no-canonicalize
Don’t canonicalize paths. The mount command canonicalizes all
paths (from the 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 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 proceed in
parallel. A disadvantage is that the order of the mount
operations is undefined. 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 mount-related
system calls. The --fake option was originally designed to
write an entry to /etc/mtab without actually mounting.
The /etc/mtab is no longer maintained in userspace, and
starting from version 2.39, the mount operation can be a
complex chain of operations with dependencies between the
syscalls. The --fake option forces libmount to skip all mount
source preparation, mount option analysis, and the actual
mounting process.
The difference between fake and non-fake execution is huge.
This is the reason why the --fake option has minimal
significance for the current mount(8) implementation and it
is maintained mostly for backward compatibility.
-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.
-m, --mkdir[=mode]
Allow to make a target directory (mountpoint) if it does not
exist yet. Alias to "-o X-mount.mkdir[=mode]", the default
mode is 0755. For more details see X-mount.mkdir below.
--map-groups, --map-users inner:_outer_:_count_
Add the specified user/group mapping to an X-mount.idmap map.
These options can be given multiple times to build up
complete mappings for users and groups. For more details see
X-mount.idmap below.
--map-users /proc/PID/ns/user
Use the specified user namespace for user and group mapping
in an id-mapped mount. This is an alias for "-o
X-mount.idmap=/proc/PID/ns/user" and cannot be used twice nor
together with the inner:_outer_:_count_ option format above.
For more details see X-mount.idmap below.
-n, --no-mtab
Mount without writing in /etc/mtab. This is necessary for
example when /etc is on a read-only filesystem.
-N, --namespace ns
Perform the mount operation in the mount namespace specified
by ns. ns is either PID of process running in that namespace
or special file representing that namespace.
mount switches to the mount namespace when it reads
/etc/fstab, writes /etc/mtab: (or writes to _/run/mount) and
calls mount(2), otherwise it runs in the original mount
namespace. This means that the target namespace does not have
to contain any libraries or other requirements necessary to
execute the mount(2) call.
See mount_namespaces(7) for more information.
-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
Note that the order of the options matters, as the last
option wins if there are conflicting ones. The options from
the command line also overwrite options from fstab by
default.
For more details, see the FILESYSTEM-INDEPENDENT MOUNT
OPTIONS and FILESYSTEM-SPECIFIC MOUNT OPTIONS sections.
--onlyonce
Forces mount command to check if the filesystem is already
mounted. This behavior is the default for --all; otherwise,
it depends on the kernel filesystem driver. Some filesystems
may be mounted more than once on the same mount point (e.g.
tmpfs).
--options-mode mode
Controls how to combine options from fstab/mtab with options
from the command line. mode can be one of ignore, append,
prepend or replace. For example, append means that options
from fstab are appended to options from the command line. The
default value is prepend — it means command line options are
evaluated after fstab options. Note that the last option wins
if there are conflicting ones.
--options-source source
Source of default options. source is a comma-separated list
of fstab, mtab and disable. disable disables fstab and mtab
and enables --options-source-force. The default value is
fstab,mtab.
--options-source-force
Use options from fstab/mtab even if both device and dir are
specified.
-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 mount operation.
-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 the target (mountpoint) or
source (device). This option allows you 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 the target (mountpoint) or
source (device). This option allows you to explicitly define
that the argument is the mount target.
--target-prefix directory
Prepend the specified directory to all mount targets. This
option can be used to follow fstab, but mount operations are
done in another place, for example:
mount --all --target-prefix /chroot -o X-mount.mkdir
mounts all from system fstab to /chroot, all missing
mountpoint are created (due to X-mount.mkdir). See also
--fstab to use an alternative fstab.
-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 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(8) 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
libblkid(3) 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 the -t option as well as in an /etc/fstab entry.
The list of filesystem types for the -t option 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. Read-write is the kernel
default and the mount default is to try read-only if the
previous mount(2) syscall with read-write flags on
write-protected devices failed.
A synonym is -o rw.
Note that specifying -w on the command line forces mount to
never try read-only mount on write-protected devices or
already mounted read-only filesystems.
-h, --help
Display help text and exit.
-V, --version
Print version 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 options nosuid, noexec, nodiratime, relatime, noatime,
strictatime, and nosymfollow are interpreted only by the abstract
VFS kernel layer and applied to the mountpoint node rather than
to the filesystem itself. Try:
findmnt -o TARGET,VFS-OPTIONS,FS-OPTIONS
to get a complete overview of filesystems and VFS options.
The read-only setting (ro or rw) is interpreted by VFS and the
filesystem and depends on how the option is specified on the
mount(8) command line. The default is to interpret it on the
filesystem level. The operation "-o bind,remount,ro" is applied
only to the VFS mountpoint, and operation "-o remount,ro" is
applied to VFS and filesystem superblock. This semantic allows
create a read-only mountpoint but keeps the filesystem writable
from another mountpoint.
Since v2.39 libmount can use a new kernel mount interface to set
the VFS options recursive. For backward compatibility, this
feature is not enabled by default, although recursive operation
(e.g. rbind) has been requested. The new option argument
"recursive" could be specified, for example:
mount -orbind,ro=recursive,noexec=recursive,nosuid /foo /bar
recursively binds filesystems from /foo to /bar, /bar, and all
submounts will be read-only and noexec, but only /bar itself will
be "nosuid". The "recursive" optional argument for VFS mount
options is an EXPERIMENTAL feature.
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, ext4,
fat, vfat, ufs and xfs):
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 or ext4 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.
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. The special value @target can be
used to assign the current context of the target mountpoint
location.
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
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 the 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
filesystem.
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(2), link(2), unlink(2), symlink(2), mkdir(2), rmdir(2),
mknod(2) and rename(2).
exec
Permit execution of binaries and other executable files.
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). This
option was deprecated in Linux 5.15.
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 or equal to the current modify or change time.
(Similar to noatime, but it doesn’t break mutt(1) 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 inode was
written to disk.
nolazytime
Do not use the lazytime feature.
suid
Honor set-user-ID and set-group-ID bits or file capabilities
when executing programs from this filesystem.
nosuid
Do not honor set-user-ID and set-group-ID bits or file
capabilities when executing programs from this filesystem. In
addition, SELinux domain transitions require permission
nosuid_transition, which in turn needs also policy capability
nnp_nosuid_transition.
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
semantics. See above, the subsection Bind mount operation.
The default kernel behavior for VFS mount flags
(nodev,nosuid,noexec,ro) is to reset all unspecified flags on
remount. That’s why mount(8) tries to keep the current
setting according to fstab or /proc/self/mountinfo. This
default behavior is possible to change by --options-mode. The
recursive change of the mount flags (supported since v2.39 on
systems with mount_setattr(2) syscall), for example, mount -o
remount,ro=recursive, do not use "reset-unspecified"
behavior, and it works as a simple add/remove operation and
unspecified flags are not modified.
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 it defaults to mount options from
/proc/self/mountinfo.
mount allows the use of --all to remount all already mounted
filesystems which match a specified filter (-O and -t). For
example:
mount --all -o remount,ro -t vfat
remounts all already mounted vfat filesystems in read-only
mode. Each of the filesystems is remounted by mount -o
remount,ro /dir semantic. This means the mount command reads
fstab or mtab and merges these options with the options from
the command line.
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 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 user
space. This means the options are also available for
umount(8) or other operations. Note that maintaining 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 for X-* now), but due to the
growing number of use-cases (in initrd, systemd etc.) the
functionality has been extended to keep existing fstab
configurations usable without a change.
X-mount.auto-fstypes=list
Specifies allowed or forbidden filesystem types for automatic
filesystem detection.
The list is a comma-separated list of the filesystem names.
The automatic filesystem detection is triggered by the "auto"
filesystem type or when the filesystem type is not specified.
The list follows how mount evaluates type patterns (see -t
for more details). Only specified filesystem types are
allowed, or all specified types are forbidden if the list is
prefixed by "no".
For example, X-mount.auto-fstypes="ext4,btrfs" accepts only
ext4 and btrfs, and X-mount.auto-fstypes="novfat,xfs" accepts
all filesystems except vfat and xfs.
Note that comma is used as a separator between mount options,
it means that auto-fstypes values have to be properly quoted,
don’t forget that the shell strips off quotes and thus double
quoting is required. For example:
mount -t auto -o’X-mount.auto-fstypes="noext2,ext3"'
/dev/sdc1 /mnt/test
X-mount.mkdir[=mode]
Allow to make a target directory (mountpoint) if it does not
exist yet. 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 or when mount is executed without suid
permissions. The option is also supported as x-mount.mkdir,
but this notation is deprecated since v2.30. See also --mkdir
command line option.
X-mount.subdir=directory
Allow mounting sub-directory from a filesystem instead of the
root directory. For now, this feature is implemented by
temporary filesystem root directory mount in unshared
namespace and then bind the sub-directory to the final mount
point and umount the root of the filesystem. The
sub-directory mount shows up atomically for the rest of the
system although it is implemented by multiple mount(2)
syscalls.
Note that this feature will not work in session with an
unshared private mount namespace (after unshare --mount) on
old kernels or with mount(8) without support for
file-descriptors-based mount kernel API. In this case, you
need unshare --mount --propagation shared.
This feature is EXPERIMENTAL.
X-mount.owner=username|UID, X-mount.group=group|GID
Set mountpoint's ownership after mounting. Names resolved in
the target mount namespace, see -N.
X-mount.mode=mode
Set mountpoint's mode after mounting.
X-mount.idmap=id-type:id-mount:id-host:id-range
[id-type:id-mount:id-host:id-range], X-mount.idmap=file
Use this option to create an idmapped mount. An idmapped
mount allows to change ownership of all files located under a
mount according to the ID-mapping associated with a user
namespace. The ownership change is tied to the lifetime and
localized to the relevant mount. The relevant ID-mapping can
be specified in two ways:
• A user can specify the ID-mapping directly.
The ID-mapping must be specified using the syntax
id-type:id-mount:id-host:id-range. Specifying u as the
id-type prefix creates a UID-mapping, g creates a
GID-mapping and omitting id-type or specifying b creates
both a UID- and GID-mapping. The id-mount parameter
indicates the starting ID in the new mount. The id-host
parameter indicates the starting ID in the filesystem.
The id-range parameter indicates how many IDs are to be
mapped. It is possible to specify multiple ID-mappings.
The individual ID-mappings must be separated by spaces.
For example, the ID-mapping X-mount.idmap=u:1000:0:1
g:1001:1:2 5000:1000:2 creates an idmapped mount where
UID 0 is mapped to UID 1000, GID 1 is mapped to GUID
1001, GID 2 is mapped to GID 1002, UID and GID 1000 are
mapped to 5000, and UID and GID 1001 are mapped to 5001
in the mount.
When an ID-mapping is specified directly a new user
namespace will be allocated with the requested
ID-mapping. The newly created user namespace will be
attached to the mount.
• A user can specify a user namespace file.
The user namespace will then be attached to the mount and
the ID-mapping of the user namespace will become the
ID-mapping of the mount.
For example, X-mount.idmap=/proc/PID/ns/user will attach
the user namespace of the process PID to the mount.
nosymfollow
Do not follow symlinks when resolving paths. Symlinks can
still be created, and readlink(1), readlink(2), realpath(1),
and realpath(3) all still work properly.
This section lists options that are specific to particular
filesystems. Where possible, you should first consult
filesystem-specific manual pages for details. Some of those pages
are listed in the following table.
┌──────────────────┬───────────────┐
│ │ │
│ Filesystem(s) │ Manual page │
├──────────────────┼───────────────┤
│ │ │
│ btrfs │ btrfs(5) │
├──────────────────┼───────────────┤
│ │ │
│ cifs │ mount.cifs(8) │
├──────────────────┼───────────────┤
│ │ │
│ ext2, ext3, ext4 │ ext4(5) │
├──────────────────┼───────────────┤
│ │ │
│ fuse │ fuse(8) │
├──────────────────┼───────────────┤
│ │ │
│ nfs │ nfs(5) │
├──────────────────┼───────────────┤
│ │ │
│ tmpfs │ tmpfs(5) │
├──────────────────┼───────────────┤
│ │ │
│ xfs │ xfs(5) │
└──────────────────┴───────────────┘
Note that some of the pages listed above might be available only
after you install the respective userland tools.
The following options apply only to certain filesystems. We sort
them by filesystem. All options follow the -o flag.
What options are supported depends a bit on the running kernel.
Further information may be available in filesystem-specific files
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.rst.
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 pseudo
terminals 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 pseudo terminals to belong to the
tty group.
mode=value
Set the mode of newly created pseudo terminals to the
specified value. The default is 0600. A value of mode=620 and
gid=5 makes "mesg y" the default on newly created pseudo
terminals.
newinstance
Create a private instance of the devpts filesystem, such that
indices of pseudo terminals 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 pseudo terminal indices (i.e., legacy mode).
Each mount of devpts with the newinstance option has a
private set of pseudo terminal 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 that the current process is owner of the
file, or that it has the CAP_FOWNER capability. But FAT
filesystems don’t have UID/GID on disk, so the normal check is
too inflexible. With this option you can relax it.
check=value
Three different levels of pickiness 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 be 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 an 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 a 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(2) 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 gives 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.
userxattr
Use the "user.overlay." xattr namespace instead of
"trusted.overlay.". This is useful for unprivileged mounting
of overlayfs.
redirect_dir={on|off|follow|nofollow}
If the redirect_dir feature is enabled, then the directory
will be copied up (but not the contents). Then the
"{trusted|user}.overlay.redirect" extended attribute is set
to the path of the original location from the root of the
overlay. Finally the directory is moved to the new location.
on
Redirects are enabled.
off
Redirects are not created and only followed if
"redirect_always_follow" feature is enabled in the
kernel/module config.
follow
Redirects are not created, but followed.
nofollow
Redirects are not created and not followed (equivalent to
"redirect_dir=off" if "redirect_always_follow" feature is
not enabled).
index={on|off}
Inode index. If this feature is disabled and a file with
multiple hard links is copied up, then this will "break" the
link. Changes will not be propagated to other names referring
to the same inode.
uuid={on|off}
Can be used to replace UUID of the underlying filesystem in
file handles with null, and effectively disable UUID checks.
This can be useful in case the underlying disk is copied and
the UUID of this copy is changed. This is only applicable if
all lower/upper/work directories are on the same filesystem,
otherwise it will fallback to normal behaviour.
nfs_export={on|off}
When the underlying filesystems supports NFS export and the
"nfs_export" feature is enabled, an overlay filesystem may be
exported to NFS.
With the "nfs_export" feature, on copy_up of any lower
object, an index entry is created under the index directory.
The index entry name is the hexadecimal representation of the
copy up origin file handle. For a non-directory object, the
index entry is a hard link to the upper inode. For a
directory object, the index entry has an extended attribute
"{trusted|user}.overlay.upper" with an encoded file handle of
the upper directory inode.
When encoding a file handle from an overlay filesystem
object, the following rules apply
• For a non-upper object, encode a lower file handle
from lower inode
• For an indexed object, encode a lower file handle
from copy_up origin
• For a pure-upper object and for an existing
non-indexed upper object, encode an upper file handle
from upper inode
The encoded overlay file handle includes
• Header including path type information (e.g.
lower/upper)
• UUID of the underlying filesystem
• Underlying filesystem encoding of underlying inode
This encoding format is identical to the encoding format of
file handles that are stored in extended attribute
"{trusted|user}.overlay.origin". When decoding an overlay
file handle, the following steps are followed
• Find underlying layer by UUID and path type
information.
• Decode the underlying filesystem file handle to
underlying dentry.
• For a lower file handle, lookup the handle in index
directory by name.
• If a whiteout is found in index, return ESTALE. This
represents an overlay object that was deleted after
its file handle was encoded.
• For a non-directory, instantiate a disconnected
overlay dentry from the decoded underlying dentry,
the path type and index inode, if found.
• For a directory, use the connected underlying decoded
dentry, path type and index, to lookup a connected
overlay dentry.
Decoding a non-directory file handle may return a
disconnected dentry. copy_up of that disconnected dentry will
create an upper index entry with no upper alias.
When overlay filesystem has multiple lower layers, a middle
layer directory may have a "redirect" to lower directory.
Because middle layer "redirects" are not indexed, a lower
file handle that was encoded from the "redirect" origin
directory, cannot be used to find the middle or upper layer
directory. Similarly, a lower file handle that was encoded
from a descendant of the "redirect" origin directory, cannot
be used to reconstruct a connected overlay path. To mitigate
the cases of directories that cannot be decoded from a lower
file handle, these directories are copied up on encode and
encoded as an upper file handle. On an overlay filesystem
with no upper layer this mitigation cannot be used NFS export
in this setup requires turning off redirect follow (e.g.
"redirect_dir=nofollow").
The overlay filesystem does not support non-directory
connectable file handles, so exporting with the subtree_check
exportfs configuration will cause failures to lookup files
over NFS.
When the NFS export feature is enabled, all directory index
entries are verified on mount time to check that upper file
handles are not stale. This verification may cause
significant overhead in some cases.
Note: the mount options index=off,nfs_export=on are
conflicting for a read-write mount and will result in an
error.
xino={on|off|auto}
The "xino" feature composes a unique object identifier from
the real object st_ino and an underlying fsid index. The
"xino" feature uses the high inode number bits for fsid,
because the underlying filesystems rarely use the high inode
number bits. In case the underlying inode number does
overflow into the high xino bits, overlay filesystem will
fall back to the non xino behavior for that inode.
For a detailed description of the effect of this option
please refer to
https://docs.kernel.org/filesystems/overlayfs.html
metacopy={on|off}
When metadata only copy up feature is enabled, overlayfs will
only copy up metadata (as opposed to whole file), when a
metadata specific operation like chown/chmod is performed.
Full file will be copied up later when file is opened for
WRITE operation.
In other words, this is delayed data copy up operation and
data is copied up when there is a need to actually modify
data.
volatile
Volatile mounts are not guaranteed to survive a crash. It is
strongly recommended that volatile mounts are only used if
data written to the overlay can be recreated without
significant effort.
The advantage of mounting with the "volatile" option is that
all forms of sync calls to the upper filesystem are omitted.
In order to avoid a giving a false sense of safety, the
syncfs (and fsync) semantics of volatile mounts are slightly
different than that of the rest of VFS. If any writeback
error occurs on the upperdir’s filesystem after a volatile
mount takes place, all sync functions will return an error.
Once this condition is reached, the filesystem will not
recover, and every subsequent sync call will return an error,
even if the upperdir has not experience a new error since the
last sync call.
When overlay is mounted with "volatile" option, the directory
"$workdir/work/incompat/volatile" is created. During next
mount, overlay checks for this directory and refuses to mount
if present. This is a strong indicator that user should throw
away upper and work directories and create fresh one. In very
limited cases where the user knows that the system has not
crashed and contents of upperdir are intact, The "volatile"
directory can be removed.
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(1) 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 filesystem. 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 OSTA,
the Optical Storage Technology Association, and is often used for
DVD-ROM, frequently in the form of a hybrid UDF/ISO-9660
filesystem. It is, however, perfectly usable by itself on disk
drives, flash drives and other block devices. See also iso9660.
uid=
Make all files in the filesystem belong to the given user.
uid=forget can be specified independently of (or usually in
addition to) uid=<user> and results in UDF not storing uids
to the media. In fact the recorded uid is the 32-bit overflow
uid -1 as defined by the UDF standard. The value is given as
either <user> which is a valid user name or the corresponding
decimal user id, or the special string "forget".
gid=
Make all files in the filesystem belong to the given group.
gid=forget can be specified independently of (or usually in
addition to) gid=<group> and results in UDF not storing gids
to the media. In fact the recorded gid is the 32-bit overflow
gid -1 as defined by the UDF standard. The value is given as
either <group> which is a valid group name or the
corresponding decimal group id, or the special string
"forget".
umask=
Mask out the given permissions from all inodes read from the
filesystem. The value is given in octal.
mode=
If mode= is set the permissions of all non-directory inodes
read from the filesystem will be set to the given mode. The
value is given in octal.
dmode=
If dmode= is set the permissions of all directory inodes read
from the filesystem will be set to the given dmode. The value
is given in octal.
bs=
Set the block size. Default value prior to kernel version
2.6.30 was 2048. Since 2.6.30 and prior to 4.11 it was
logical device block size with fallback to 2048. Since 4.11
it is logical block size with fallback to any valid block
size between logical device block size and 4096.
For other details see the mkudffs(8) 2.0+ manpage, see the
COMPATIBILITY and BLOCK SIZE sections.
unhide
Show otherwise hidden files.
undelete
Show deleted files in lists.
adinicb
Embed data in the inode. (default)
noadinicb
Don’t embed data in the inode.
shortad
Use short UDF address descriptors.
longad
Use long UDF address descriptors. (default)
nostrict
Unset strict conformance.
iocharset=
Set the NLS character set. This requires kernel compiled with
CONFIG_UDF_NLS option.
utf8
Set the UTF-8 character set.
Mount options for debugging and disaster recovery
novrs
Ignore the Volume Recognition Sequence and attempt to mount
anyway.
session=
Select the session number for multi-session recorded optical
media. (default= last session)
anchor=
Override standard anchor location. (default= 256)
lastblock=
Set the last block of the filesystem.
Unused historical mount options that may be encountered and should be
removed
uid=ignore
Ignored, use uid=<user> instead.
gid=ignore
Ignored, use gid=<group> instead.
volume=
Unimplemented and ignored.
partition=
Unimplemented and ignored.
fileset=
Unimplemented and ignored.
rootdir=
Unimplemented and ignored.
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 macOS.
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.
The device-mapper verity target provides read-only transparent
integrity checking of block devices using kernel crypto API. The
mount command can open the dm-verity device and do the integrity
verification before the device filesystem is mounted. Requires
libcryptsetup with in libmount (optionally via dlopen(3)). If
libcryptsetup supports extracting the root hash of an already
mounted device, existing devices will be automatically reused in
case of a match. Mount options for dm-verity:
verity.hashdevice=path
Path to the hash tree device associated with the source
volume to pass to dm-verity.
verity.roothash=hex
Hex-encoded hash of the root of verity.hashdevice. Mutually
exclusive with verity.roothashfile.
verity.roothashfile=path
Path to file containing the hex-encoded hash of the root of
verity.hashdevice. Mutually exclusive with verity.roothash.
verity.hashoffset=offset
If the hash tree device is embedded in the source volume,
offset (default: 0) is used by dm-verity to get to the tree.
verity.fecdevice=path
Path to the Forward Error Correction (FEC) device associated
with the source volume to pass to dm-verity. Optional.
Requires kernel built with CONFIG_DM_VERITY_FEC.
verity.fecoffset=offset
If the FEC device is embedded in the source volume, offset
(default: 0) is used by dm-verity to get to the FEC area.
Optional.
verity.fecroots=value
Parity bytes for FEC (default: 2). Optional.
verity.roothashsig=path
Path to pkcs7(1ssl) signature of root hash hex string.
Requires crypt_activate_by_signed_key() from cryptsetup and
kernel built with CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG. For
device reuse, signatures have to be either used by all mounts
of a device or by none. Optional.
verity.oncorruption=ignore|restart|panic
Instruct the kernel to ignore, reboot or panic when
corruption is detected. By default the I/O operation simply
fails. Requires Linux 4.1 or newer, and libcrypsetup 2.3.4 or
newer. Optional.
Supported since util-linux v2.35.
For example commands:
mksquashfs /etc /tmp/etc.raw
veritysetup format /tmp/etc.raw /tmp/etc.verity --root-hash-file=/tmp/etc.roothash
openssl smime -sign -in /tmp/etc.roothash -nocerts -inkey private.key \
-signer private.crt -noattr -binary -outform der -out /tmp/etc.roothash.p7s
mount -o verity.hashdevice=/tmp/etc.verity,verity.roothashfile=/tmp/etc.roothash,\
verity.roothashsig=/tmp/etc.roothash.p7s /tmp/etc.raw /mnt
create squashfs image from /etc directory, verity hash device and
mount verified filesystem image to /mnt. The kernel will verify
that the root hash is signed by a key from the kernel keyring if
roothashsig is used.
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 ext4 /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 re-uses the loop device rather than
initializing 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 exit status values (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).
126
failed to execute external /sbin/mount.<type> mount helper
(since util-linux v2.41)
The syntax of external mount helpers is:
/sbin/mount.suffix spec dir [-sfnv] [-N namespace] [-o options]
[-t type.subtype]
where the suffix is the filesystem type and the -sfnvoN 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 an argument to the -o option.
The exit status value of the helper is returned as the exit
status of mount(8). The value 126 is sed if the mount helper
program is found, but the execl() failed.
LIBMOUNT_FORCE_MOUNT2={always|never|auto}
force to use classic mount(2) system call (requires support
for new file descriptors based mount API). The default is
auto; in this case, libmount tries to be smart and use
classic mount(2) only for well-known issues. If the new mount
API is unavailable, libmount can still use traditional
mount(2), although LIBMOUNT_FORCE_MOUNT2 is set to never.
LIBMOUNT_FSTAB=<path>
overrides the default location of the fstab 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
See also "The files /etc/fstab, /etc/mtab and /proc/mounts"
section above.
/etc/fstab
filesystem table
/run/mount
libmount private runtime directory
/etc/mtab
table of mounted filesystems or symlink to /proc/mounts
/etc/mtab~
lock file (unused on systems with mtab symlink)
/etc/mtab.tmp
temporary file (unused on systems with mtab symlink)
/etc/filesystems
a list of filesystem types to try
A mount command existed in Version 5 AT&T UNIX.
It is possible for a corrupted filesystem to cause a crash.
Some Linux filesystems don’t support -o sync and -o dirsync (the
ext2, ext3, ext4, 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/mount 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 the noac mount option 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(8) command manually before calling mount with the
configured loop device.
Karel Zak <[email protected]>
mount(2), umount(2), filesystems(5), fstab(5), nfs(5), xfs(5),
mount_namespaces(7), xattr(7), e2label(8), findmnt(8),
losetup(8), lsblk(8), mke2fs(8), mountd(8), nfsd(8), swapon(8),
tune2fs(8), umount(8), xfs_admin(8)
For bug reports, use the issue tracker at
https://github.com/util-linux/util-linux/issues.
The mount command is part of the util-linux package which can be
downloaded from Linux Kernel Archive
<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
[email protected]. This page was obtained from the
project's upstream Git repository
⟨git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git⟩ on
2024-06-14. (At that time, the date of the most recent commit
that was found in the repository was 2024-06-10.) 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 [email protected]
util-linux 2.41.devel-537-e... 2024-06-13 MOUNT(8)
Pages that refer to this page: eject(1), fusermount3(1), homectl(1), mountpoint(1), quotasync(1), systemd-dissect(1), systemd-mount(1), unshare(1), chown(2), fcntl(2), FS_IOC_SETFLAGS(2const), fsync(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), nfs(5), nfsmount.conf(5), proc(5), proc_filesystems(5), repart.d(5), systemd.automount(5), systemd.exec(5), systemd.mount(5), tmpfs(5), xfs(5), bootparam(7), fanotify(7), file-hierarchy(7), hier(7), inode(7), man-pages(7), mount_namespaces(7), spufs(7), automount(8), blkid(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), mount(8), mount.fuse3(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), wipefs(8), xfs_admin(8), xfs_db(8), xfs_freeze(8), xfs_growfs(8), xfs_info(8), xfs_logprint(8), xfs_rtcp(8)
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