mount(8) — Arch manual pages

mount(8) — Arch manual pages
MOUNT(8)
System Administration
MOUNT(8)
NAME
mount - mount a filesystem
SYNOPSIS
mount
-h
-V
mount
-l
] [
-t
fstype
mount
-a
-F
] [
-fnrsvw
] [
-t
fstype
] [
-O
optlist
mount
-fnrsvw
] [
-o
options
device
mountpoint
mount
-fnrsvw
] [
-o
options
-t
fstype
device mountpoint
mount
--bind
--rbind
--move
olddir
newdir
mount
--make-
]{
shared
slave
private
unbindable
mountpoint
DESCRIPTION
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

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.) 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
COMMAND-LINE OPTIONS
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).
This option was originally designed for use in init scripts. Note that many
modern systemd-based distributions do not use
mount -a
on boot and
instead mount filesystems in a more sophisticated way using systemd units.
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 swap entries in
fstab
are silently ignored by
mount -a
. Use
swapon -a
to enable swap devices and files. See
swapon(8)
Note that it is a bad practice to use
mount -a
for
fstab
checking. The recommended solution is
findmnt
--verify
--beneath
Mount the filesystem beneath the top mount of the
specified target (mountpoint), allowing the top mount to be unmounted. This
option replaces the filesystem at the mountpoint in an atomic manner, ensuring
there is no moment when the filesystem is absent.
For example update from a Btrfs filesystem to an XFS filesystem
without ever revealing the underlying mountpoint:
mount -t btrfs /dev/sdA /mnt
mount --beneath -t xfs /dev/sdB /mnt
umount /mnt
-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
Do not canonicalize any paths or tags during the mount
process. The
mount
command automatically canonicalizes all paths (from
the command line or
fstab
). This option can be used in conjunction with
the
-f
flag for paths that are already canonicalized. This option is
intended for mount helpers that call
mount -i
. It is highly recommended
to not use this command-line option for regular mount operations. See also the
X-mount.nocanonicalize mount options.
Note that
mount
does not pass this option to the
/sbin/mount.
type
helpers.
--exclusive
Ensures that the filesystem is mounted as a unique
instance and that the filesystem superblock is not reused by the kernel. The
filesystem may be reused later if mounted without the option. The option
affects only the current mount and is allowed for non-root users as well.
See also the
--onlyonce
option. The difference between
--onlyonce
and
--exclusive
is that "onlyonce"
ensures the same source is not mounted on the same mount point; this means
mounting twice on /A is not allowed, but mounting on /A and /B is allowed.
The "exclusive" mount ensures the filesystem itself is not reused,
regardless of the mount point.
-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 the PID of the process running in
that namespace or a 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. Also, options on the command line
override options from fstab.
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 on specified mountpoint. 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). See also
--exclusive
--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
--ro
--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
Enables verbose mode. Starting from version 2.41, if the
new kernel mount API is available, it will also print kernel info
messages.
-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
Display version and exit.
FILESYSTEM-INDEPENDENT MOUNT OPTIONS
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
ext
filesystems).
Virtual Filesystem Notes
The Virtual File System (VFS) is the abstract layer in the kernel
that provides the filesystem interface to userspace programs. It also
provides an abstraction within the kernel which allows different filesystem
implementations to coexist. Some of the mount options only apply to this
layer.
The options
nosuid
noexec
nodiratime
relatime
noatime
strictatime
, and
nosymfollow
are interpreted only by the virtual-filesystem kernel layer and are applied
to the mountpoint node rather than to the filesystem itself. To get a
complete overview of filesystems and VFS options, try:
findmnt -o TARGET,VFS-OPTIONS,FS-OPTIONS
Since v2.39, libmount can use a new kernel mount interface to set
the VFS attributes recursively. For backward compatibility, this feature is
not enabled by default, even if recursive operation (e.g. rbind) has been
requested. The new option argument "recursive" can be specified,
for example:
mount -orbind,ro=recursive,noexec=recursive,nosuid /foo /bar
This recursively binds filesystems from /foo to /bar, making /bar
and all submounts read-only and noexec, but only /bar itself will be
"nosuid". The "recursive" optional argument for VFS
mount options is an EXPERIMENTAL feature.
Read-only Setting Notes
The read-only setting (
ro
or
rw
) is interpreted by
the virtual-filesystem and the filesystem, and it depends on how the option
is specified on the
mount(8)
command line. For backward
compatibility, the default is to use it for both layers during standard
mount operations.
The operation "-o bind,remount,ro" is applied only to
the VFS mountpoint, while the operation "-o remount,ro" is applied
to both the VFS and filesystem superblock. This semantic allows for the
creation of a read-only mountpoint while keeping the filesystem writable
from another mountpoint.
Since version 2.41, libmount has the ability to use optional
arguments
vfs
and
fs
(e.g. ro=fs) to specify where the
read-only setting should be applied. For example, using the command:
mount -o ro=vfs /dev/sdc1 /A
will mount the filesystem as read-write on the superblock level,
but the /A node will be set as read-only. In previous versions, this
required an additional "-o bind,remount,ro" operation to achieve
the same result.
Generic Mount Options
The following options apply to any filesystem that is being
mounted, but not every filesystem actually honors them. For example, the
sync
option only has an effect on ext2, ext3, ext4, fat, vfat, ufs,
and xfs filesystems.
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. 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
recursive
vfs
fs
)]
Mount the filesystem read-only. The optional argument is
an experimental feature supported only by the file-descriptor based kernel
mount API and it is silently ignored for the old
mount(2)
syscall.
The
recursive
argument forces the VFS attribute to be
applied recursively.
The
vfs
and
fs
arguments specify the layer where the
read-only flag should be applied. The
fs
specifies the filesystem
superblock (unique filesystem instance in the kernel), and
vfs
specifies the mount node. If no attribute is specified, then both layers are
set to read-only.
For more details, please refer to the
Read-only Setting
Notes
section.
rw
recursive
vfs
fs
)]
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 to 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.nocanonicalize
type
Allows disabling of canonicalization for mount source and
target paths. By default, the
mount
command resolves
all paths to their absolute paths without symlinks. However, this behavior may
not be desired in certain situations, such as when binding a mount over a
symlink, or a symlink over a directory or another symlink. The optional
argument
type
can be either "source" or "target"
(mountpoint). If no
type
is specified, then canonicalization is
disabled for both types. This mount option does not affect the conversion of
source tags (e.g.
LABEL=
or
UUID=
) and
fstab
processing.
The command-line option
--no-canonicalize
overrides this
mount option and affects all path and tag conversions in all situations, but
for backward compatibility, it does not modify
open_tree(2)
syscall
flags and does not allow the bind-mount over a symlink use case.
Note that
mount(8)
still sanitizes and canonicalizes the
source and target paths specified on the command line by non-root users,
regardless of the X-mount.nocanonicalize setting.
X-mount.noloop
Do not create and mount a loop device, even if the source
of the mount is a regular file.
X-mount.subdir=
directory
Allow mounting a subdirectory of a filesystem instead of
the root directory. This is effective only when a new instance of a filesystem
is attached to the system. The option is silently ignored for operations like
remount, bind mount, or move.
For now, this feature is implemented by a temporary filesystem
root-directory mount in an unshared namespace and then binding the
sub-directory to the final mount point and unmounting 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
as the
id-type
prefix creates a UID-mapping,
creates a GID-mapping and omitting
id-type
or specifying
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. Please
note that in the
/etc/fstab
file, spaces are interpreted as
separators between fields. To avoid this, you must escape them using \040.
For example, X-mount.idmap=0:0:1\040500:1000:1.
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.
FILESYSTEM-SPECIFIC MOUNT OPTIONS
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)
cephfs
mount.ceph(8)
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=
, gid=
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/
.
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.
Possible values:
20
If the current process is in the group of the
file’s group ID, you can change the timestamp.
Other users can change the timestamp.
The default is set from the above
dmask
option. (If the
directory is writable,
utime(2)
is also allowed. That is: ~dmask
& 022.)
Normally
utime(2)
checks that the current process is the
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:
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).
ormal
Like "relaxed", but many special characters (*,
?, <, spaces, etc.) are rejected. This is the default.
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=
, gid=
Set the owner and group of all files. (Default: the UID
and GID of the current process.)
dir_umask=
, file_umask=
umask=
Set the umask used for all directories, all regular
files, or all files and directories. Defaults to the umask of the current
process.
session=
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=
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=
elaxed
]|
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=
ormal
]|
ff
]|
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=
Select number of session on a multisession CD, starting
with 0.
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 ntfs3
The ntfs3 kernel driver provides below mount options - as
documented in
iocharset=
name
This option informs the driver how to interpret path
strings and translate them to Unicode and back. If this option is not set, the
default codepage will be used (CONFIG_NLS_DEFAULT).
Example: iocharset=utf8
uid=
gid=
umask=
Controls the default permissions for files/directories
created after the NTFS volume is mounted.
dmask=
fmask=
Instead of specifying umask which applies both to files
and directories, fmask applies only to files and dmask only to
directories.
nohidden
Files with the Windows-specific HIDDEN
(FILE_ATTRIBUTE_HIDDEN) attribute will not be shown under Linux.
sys_immutable
Files with the Windows-specific SYSTEM
(FILE_ATTRIBUTE_SYSTEM) attribute will be marked as system immutable
files.
hide_dot_files
Updates the Windows-specific HIDDEN
(FILE_ATTRIBUTE_HIDDEN) attribute when creating and moving or renaming files.
Files whose names start with a dot will have the HIDDEN attribute set and
files whose names do not start with a dot will have it unset.
windows_names
Prevents the creation of files and directories with a
name not allowed by Windows, either because it contains some not allowed
character (which are the characters “ * / : < > ? \ | and those
whose code is less than 0x20), because the name (with or without extension) is
a reserved file name (CON, AUX, NUL, PRN, LPT1-9, COM1-9) or because the last
character is a space or a dot. Existing such files can still be read and
renamed.
discard
Enable support of the TRIM command for improved
performance on delete operations, which is recommended for use with the
solid-state drives (SSD).
force
Forces the driver to mount partitions even if volume is
marked dirty. Not recommended for use.
sparse
Create new files as sparse.
showmeta
Use this parameter to show all meta-files (System Files)
on a mounted NTFS partition. By default, all meta-files are hidden.
prealloc
Preallocate space for files excessively when file size is
increasing on writes. Decreases fragmentation in case of parallel write
operations to different files.
acl
Support POSIX ACLs (Access Control Lists). Effective if
supported by Kernel. Not to be confused with NTFS ACLs. The option specified
as acl enables support for POSIX ACLs.
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
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

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
, volume number
ubiY
UBI device number
, volume number
ubiX:NAME
UBI device number
, volume with name
NAME
ubi:NAME
UBI device number
, 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= 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 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= 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 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= instead.
gid=ignore
Ignored, use gid= 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
mode
s:
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.
DM-VERITY SUPPORT
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, the 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.
LOOP-DEVICE SUPPORT
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.
EXIT STATUS
mount
has the following exit status values (the bits can be
ORed):
success
incorrect invocation or permissions
system error (out of memory, cannot fork, no more loop
devices)
internal
mount
bug
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. mount
helper (since util-linux v2.41)
EXTERNAL HELPERS
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. 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.
ENVIRONMENT
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
=
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
FILES
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
HISTORY
mount
command existed in Version 5 AT&T UNIX.
BUGS
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.
AUTHORS
Karel Zak

SEE ALSO
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)
REPORTING BUGS
For bug reports, use the
issue tracker
AVAILABILITY
The
mount
command is part of the util-linux package which
can be downloaded from
Linux Kernel Archive
2026-04-01
util-linux 2.42
Package information:
Package name:
core/util-linux
Version:
2.42-1
Upstream:
Licenses:
BSD-2-Clause, BSD-3-Clause, BSD-4-Clause-UC, GPL-2.0-only, GPL-2.0-or-later, GPL-3.0-or-later, ISC, LGPL-2.1-or-later, LicenseRef-PublicDomain
Manuals:
/listing/core/util-linux/
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