MOUNT(8) System Administration MOUNT(8)
mount - mount a filesystem
mount [-h|-V]
mount [-l] [-t fstype]
mount -a [-fFnrsvw] [-t fstype] [-O optlist]
mount [-fnrsvw] [-o options] device|mountpoint
mount [-fnrsvw] [-t fstype] [-o options] device mountpoint
mount --bind|--rbind|--move olddir newdir
mount
--make-{shared|slave|private|unbindable|rshared|rslave|rprivate|runbindable}
mountpoint
All files accessible in a Unix system are arranged in one big
tree, the file hierarchy, rooted at /. These files can be spread
out over several devices. The mount command serves to attach the
filesystem found on some device to the big file tree.
Conversely, the umount(8) command will detach it again. The
filesystem is used to control how data is stored on the device or
provided in a virtual way by network or other services.
The standard form of the mount command is:
mount -t type device dir
This tells the kernel to attach the filesystem found on device
(which is of type type) at the directory dir. The option -t type
is optional. The mount command is usually able to detect a
filesystem. The root permissions are necessary to mount a
filesystem by default. See section "Non-superuser mounts" below
for more details. The previous contents (if any) and owner and
mode of dir become invisible, and as long as this filesystem
remains mounted, the pathname dir refers to the root of the
filesystem on device.
If only the directory or the device is given, for example:
mount /dir
then mount looks for a mountpoint (and if not found then for a
device) in the /etc/fstab file. It's possible to use the
--target or --source options to avoid ambiguous interpretation of
the given argument. For example:
mount --target /mountpoint
The same filesystem may be mounted more than once, and in some
cases (e.g., network filesystems) the same filesystem may be
mounted on the same mountpoint multiple times. The mount command
does not implement any policy to control this behavior. All
behavior is controlled by the kernel and it is usually specific
to the filesystem driver. The exception is --all, in this case
already mounted filesystems are ignored (see --all below for more
details).
Listing the mounts
The listing mode is maintained for backward compatibility only.
For more robust and customizable output use findmnt(8),
especially in your scripts. Note that control characters in the
mountpoint name are replaced with '?'.
The following command lists all mounted filesystems (of type
type):
mount [-l] [-t type]
The option -l adds labels to this listing. See below.
Indicating the device and filesystem
Most devices are indicated by a filename (of a block special
device), like /dev/sda1, but there are other possibilities. For
example, in the case of an NFS mount, device may look like
knuth.cwi.nl:/dir.
The device names of disk partitions are unstable; hardware
reconfiguration, and adding or removing a device can cause
changes in names. This is the reason why it's strongly
recommended to use filesystem or partition identifiers like UUID
or LABEL. Currently supported identifiers (tags):
LABEL=label
Human readable filesystem identifier. See also -L.
UUID=uuid
Filesystem universally unique identifier. The
format of the UUID is usually a series of hex
digits separated by hyphens. See also -U.
Note that mount(8) uses UUIDs as strings. The
UUIDs from the command line or from fstab(5) are
not converted to internal binary representation.
The string representation of the UUID should be
based on lower case characters.
PARTLABEL=label
Human readable partition identifier. This
identifier is independent on filesystem and does
not change by mkfs or mkswap operations It's
supported for example for GUID Partition Tables
(GPT).
PARTUUID=uuid
Partition universally unique identifier. This
identifier is independent on filesystem and does
not change by mkfs or mkswap operations It's
supported for example for GUID Partition Tables
(GPT).
ID=id Hardware block device ID as generated by udevd.
This identifier is usually based on WWN (unique
storage identifier) and assigned by the hardware
manufacturer. See ls /dev/disk/by-id for more
details, this directory and running udevd is
required. This identifier is not recommended for
generic use as the identifier is not strictly
defined and it depends on udev, udev rules and
hardware.
The command lsblk --fs provides an overview of filesystems,
LABELs and UUIDs on available block devices. The command blkid
-p <device> provides details about a filesystem on the specified
device.
Don't forget that there is no guarantee that UUIDs and labels are
really unique, especially if you move, share or copy the device.
Use lsblk -o +UUID,PARTUUID to verify that the UUIDs are really
unique in your system.
The recommended setup is to use tags (e.g. UUID=uuid) rather than
/dev/disk/by-{label,uuid,id,partuuid,partlabel} udev symlinks in
the /etc/fstab file. Tags are more readable, robust and
portable. The mount(8) command internally uses udev symlinks, so
the use of symlinks in /etc/fstab has no advantage over tags.
For more details see libblkid(3).
The proc filesystem is not associated with a special device, and
when mounting it, an arbitrary keyword—for example, proc—can be
used instead of a device specification. (The customary choice
none is less fortunate: the error message `none already mounted'
from mount can be confusing.)
The files /etc/fstab, /etc/mtab and /proc/mounts
The file /etc/fstab (see fstab(5)), may contain lines describing
what devices are usually mounted where, using which options. The
default location of the fstab(5) file can be overridden with the
--fstab path command-line option (see below for more details).
The command
mount -a [-t type] [-O optlist]
(usually given in a bootscript) causes all filesystems mentioned
in fstab (of the proper type and/or having or not having the
proper options) to be mounted as indicated, except for those
whose line contains the noauto keyword. Adding the -F option
will make mount fork, so that the filesystems are mounted in
parallel.
When mounting a filesystem mentioned in fstab or mtab, it
suffices to specify on the command line only the device, or only
the mount point.
The programs mount and umount 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.
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(8) 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 and relatime VFS entry flags via a "remount,bind"
operation. The other flags (for example filesystem-specific
flags) are silently ignored. It's impossible to change mount
options recursively (for example with -o rbind,ro).
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(8) behavior does not affect situations when "remount,bind"
is specified in the /etc/fstab file.
The move operation
Move a mounted tree to another place (atomically). The call is:
mount --move olddir newdir
This will cause the contents which previously appeared under
olddir to now be accessible under newdir. The physical location
of the files is not changed. Note that olddir has to be a
mountpoint.
Note also that moving a mount residing under a shared mount is
invalid and unsupported. Use findmnt -o TARGET,PROPAGATION to
see the current propagation flags.
Shared subtree operations
Since Linux 2.6.15 it is possible to mark a mount and its
submounts as shared, private, slave or unbindable. A shared
mount provides the ability to create mirrors of that mount such
that mounts and unmounts within any of the mirrors propagate to
the other mirror. A slave mount receives propagation from its
master, but not vice versa. A private mount carries no
propagation abilities. An unbindable mount is a private mount
which cannot be cloned through a bind operation. The detailed
semantics are documented in
Documentation/filesystems/sharedsubtree.txt file in the kernel
source tree; 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(8) does not read fstab(5) when a --make-* operation is
requested. All necessary information has to be specified on the
command line.
Note that the Linux kernel does not allow 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. This feature is
EXPERIMENTAL. The propagation flags are applied by additional
mount(2) system calls when the preceding mount operations were
successful. Note that this use case is not atomic. It is
possible to specify the propagation flags in fstab(5) as mount
options (private, slave, shared, unbindable, rprivate, rslave,
rshared, runbindable).
For example:
mount --make-private --make-unbindable /dev/sda1 /foo
is the same as:
mount /dev/sda1 /foo
mount --make-private /foo
mount --make-unbindable /foo
The full set of mount options used by an invocation of mount is
determined by first extracting the mount options for the
filesystem from the fstab table, then applying any options
specified by the -o argument, and finally applying a -r or -w
option, when present.
The 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 section EXTERNAL
HELPERS.
Command-line options available for the mount command are:
-a, --all
Mount all filesystems (of the given types) mentioned in
fstab (except for those whose line contains the noauto
keyword). The filesystems are mounted following their
order in fstab. 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 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 is possible to use the command line
option -o to alter mount options from fstab (see also
--options-mode).
Note that it is a bad practice to use mount -a for fstab
checking. The recommended solution is findmnt --verify.
-B, --bind
Remount a subtree somewhere else (so that its contents are
available in both places). See above, under Bind mounts.
-c, --no-canonicalize
Don't canonicalize paths. The mount command canonicalizes
all paths (from the command line or fstab) by default.
This option can be used together with the -f flag for
already canonicalized absolute paths. The option is
designed for mount helpers which call mount -i. It is
strongly recommended to not use this command-line option
for normal mount operations.
Note that mount(8) does not pass this option to the
/sbin/mount.type helpers.
-F, --fork
(Used in conjunction with -a.) Fork off a new incarnation
of mount for each device. This will do the mounts on
different devices or different NFS servers in parallel.
This has the advantage that it is faster; also NFS
timeouts 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 actual system
call; if it's not obvious, this ``fakes'' mounting the
filesystem. This option is useful in conjunction with the
-v flag to determine what the mount command is trying to
do. It can also be used to add entries for devices that
were mounted earlier with the -n option. The -f option
checks for an existing record in /etc/mtab and fails when
the record already exists (with a regular non-fake mount,
this check is done by the kernel).
-i, --internal-only
Don't call the /sbin/mount.filesystem helper even if it
exists.
-L, --label label
Mount the partition that has the specified label.
-l, --show-labels
Add the labels in the mount output. mount must have
permission to read the disk device (e.g. be set-user-ID
root) for this to work. One can set such a label for
ext2, ext3 or ext4 using the e2label(8) utility, or for
XFS using xfs_admin(8), or for reiserfs using
reiserfstune(8).
-M, --move
Move a subtree to some other place. See above, the
subsection The move operation.
-n, --no-mtab
Mount without writing in /etc/mtab. This is necessary for
example when /etc is on a read-only filesystem.
-N, --namespace ns
Perform the mount operation in the mount namespace
specified by ns. ns is either PID of process running in
that namespace or special file representing that
namespace.
mount(8) switches to the mount namespace when it reads
/etc/fstab, writes /etc/mtab (or writes to /run/mount) and
calls the mount(2) system call, 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
For more details, see the FILESYSTEM-INDEPENDENT MOUNT
OPTIONS and FILESYSTEM-SPECIFIC MOUNT OPTIONS sections.
--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 disables --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 mounts.
-r, --read-only
Mount the filesystem read-only. A synonym is -o ro.
Note that, depending on the filesystem type, state and
kernel behavior, the system may still write to the device.
For example, ext3 and ext4 will replay the journal if the
filesystem is dirty. To prevent this kind of write
access, you may want to mount an ext3 or ext4 filesystem
with the ro,noload mount options or set the block device
itself to read-only mode, see the blockdev(8) command.
-s Tolerate sloppy mount options rather than failing. This
will ignore mount options not supported by a filesystem
type. Not all filesystems support this option. Currently
it's supported by the mount.nfs mount helper only.
--source device
If only one argument for the mount command is given, then
the argument might be interpreted as 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(8) does not pass the option --fstab to the
/sbin/mount.type helpers, meaning that the alternative
fstab files will be invisible for the helpers. This is no
problem for normal mounts, but user (non-root) mounts
always require fstab to verify the user's rights.
-t, --types fstype
The argument following the -t is used to indicate the
filesystem type. The filesystem types which are currently
supported depend on the running kernel. See
/proc/filesystems and /lib/modules/$(uname -r)/kernel/fs
for a complete list of the filesystems. The most common
are ext2, ext3, ext4, xfs, btrfs, vfat, sysfs, proc, nfs
and cifs.
The programs mount and umount support filesystem subtypes.
The subtype is defined by a '.subtype' suffix. For
example 'fuse.sshfs'. It's recommended to use subtype
notation rather than add any prefix to the mount source
(for example 'sshfs#example.com' is deprecated).
If no -t option is given, or if the auto type is
specified, mount will try to guess the desired type.
Mount uses the blkid library for guessing the filesystem
type; if that does not turn up anything that looks
familiar, mount will try to read the file
/etc/filesystems, or, if that does not exist,
/proc/filesystems. All of the filesystem types listed
there will be tried, except for those that are labeled
"nodev" (e.g. devpts, proc and nfs). If /etc/filesystems
ends in a line with a single *, mount will read
/proc/filesystems afterwards. While trying, all
filesystem types will be mounted with the mount option
silent.
The auto type may be useful for user-mounted floppies.
Creating a file /etc/filesystems can be useful to change
the probe order (e.g., to try vfat before msdos or ext3
before ext2) or if you use a kernel module autoloader.
More than one type may be specified in a comma-separated
list, for the -t option as well as in an /etc/fstab entry.
The list of filesystem types for the -t option can be
prefixed with no to specify the filesystem types on which
no action should be taken. The prefix no has no effect
when specified in an /etc/fstab entry.
The prefix no can be meaningful with the -a option. For
example, the command
mount -a -t nomsdos,smbfs
mounts all filesystems except those of type msdos and
smbfs.
For most types all the mount program has to do is issue a
simple mount(2) system call, and no detailed knowledge of
the filesystem type is required. For a few types however
(like nfs, nfs4, cifs, smbfs, ncpfs) an ad hoc code is
necessary. The nfs, nfs4, cifs, smbfs, and ncpfs
filesystems have a separate mount program. In order to
make it possible to treat all types in a uniform way,
mount will execute the program /sbin/mount.type (if that
exists) when called with type type. Since different
versions of the smbmount program have different calling
conventions, /sbin/mount.smbfs may have to be a shell
script that sets up the desired call.
-U, --uuid uuid
Mount the partition that has the specified uuid.
-v, --verbose
Verbose mode.
-w, --rw, --read-write
Mount the filesystem read/write. Read-write is the kernel
default and the mount default is to try read-only if the
previous mount syscall with read-write flags on write-
protected devices of filesystems 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.
-V, --version
Display version information and exit.
-h, --help
Display help text and exit.
Some of these options are only useful when they appear in the
/etc/fstab file.
Some of these options could be enabled or disabled by default in
the system kernel. To check the current setting see the options
in /proc/mounts. Note that filesystems also have per-filesystem
specific default mount options (see for example tune2fs -l output
for extN filesystems).
The following options apply to any filesystem that is being
mounted (but not every filesystem actually honors them – e.g.,
the sync option today has an effect only for ext2, ext3, ext4,
fat, vfat, ufs and xfs):
async All I/O to the filesystem should be done asynchronously.
(See also the sync option.)
atime Do not use the noatime feature, so the inode access time
is controlled by kernel defaults. See also the
descriptions of the relatime and strictatime mount
options.
noatime
Do not update inode access times on this filesystem (e.g.
for faster access on the news spool to speed up news
servers). This works for all inode types (directories
too), so it implies nodiratime.
auto Can be mounted with the -a option.
noauto Can only be mounted explicitly (i.e., the -a option will
not cause the filesystem to be mounted).
context=context, fscontext=context, defcontext=context, and
rootcontext=context
The context= option is useful when mounting filesystems
that do not support extended attributes, such as a floppy
or hard disk formatted with VFAT, or systems that are not
normally running under SELinux, such as an ext3 or ext4
formatted disk from a non-SELinux workstation. You can
also use context= on filesystems you do not trust, such as
a floppy. It also helps in compatibility with xattr-
supporting filesystems on earlier 2.4.<x> kernel versions.
Even where xattrs are supported, you can save time not
having to label every file by assigning the entire disk
one security context.
A commonly used option for removable media is
context="system_u:object_r:removable_t".
Two other options are fscontext= and defcontext=, both of
which are mutually exclusive of the context= option. This
means you can use fscontext and defcontext with each
other, but neither can be used with context.
The fscontext= option works for all filesystems,
regardless of their xattr support. The fscontext option
sets the overarching filesystem label to a specific
security context. This filesystem label is separate from
the individual labels on the files. It represents the
entire filesystem for certain kinds of permission checks,
such as during mount or file creation. Individual file
labels are still obtained from the xattrs on the files
themselves. The context option actually sets the
aggregate context that fscontext provides, in addition to
supplying the same label for individual files.
You can set the default security context for unlabeled
files using defcontext= option. This overrides the value
set for unlabeled files in the policy and requires a
filesystem that supports xattr labeling.
The rootcontext= option allows you to explicitly label the
root inode of a FS being mounted before that FS or inode
becomes visible to userspace. This was found to be useful
for things like stateless Linux.
Note that the kernel rejects any remount request that
includes the context option, even when unchanged from the
current context.
Warning: the context value might contain commas, in which
case the value has to be properly quoted, otherwise
mount(8) will interpret the comma as a separator between
mount options. Don't forget that the shell strips off
quotes and thus double quoting is required. For example:
mount -t tmpfs none /mnt -o \
'context="system_u:object_r:tmp_t:s0:c127,c456",noexec'
For more details, see selinux(8).
defaults
Use the default options: rw, suid, dev, exec, auto,
nouser, and async.
Note that the real set of all default mount options
depends on 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, link, unlink, symlink, mkdir, rmdir, mknod and
rename.
exec Permit execution of binaries.
noexec Do not permit direct execution of any binaries on the
mounted filesystem.
group Allow an ordinary user to mount the filesystem if one of
that user's groups matches the group of the device. This
option implies the options nosuid and nodev (unless
overridden by subsequent options, as in the option line
group,dev,suid).
iversion
Every time the inode is modified, the i_version field will
be incremented.
noiversion
Do not increment the i_version inode field.
mand Allow mandatory locks on this filesystem. See fcntl(2).
nomand Do not allow mandatory locks on this filesystem.
_netdev
The filesystem resides on a device that requires network
access (used to prevent the system from attempting to
mount these filesystems until the network has been enabled
on the system).
nofail Do not report errors for this device if it does not exist.
relatime
Update inode access times relative to modify or change
time. Access time is only updated if the previous access
time was earlier than the current modify or change time.
(Similar to noatime, but it doesn't break mutt or other
applications that need to know if a file has been read
since the last time it was modified.)
Since Linux 2.6.30, the kernel defaults to the behavior
provided by this option (unless noatime was specified),
and the strictatime option is required to obtain
traditional semantics. In addition, since Linux 2.6.30,
the file's last access time is always updated if it is
more than 1 day old.
norelatime
Do not use the relatime feature. See also the strictatime
mount option.
strictatime
Allows to explicitly request full atime updates. This
makes it possible for the kernel to default to relatime or
noatime but still allow userspace to override it. For
more details about the default system mount options see
/proc/mounts.
nostrictatime
Use the kernel's default behavior for inode access time
updates.
lazytime
Only update times (atime, mtime, ctime) on the in-memory
version of the file inode.
This mount option significantly reduces writes to the
inode table for workloads that perform frequent random
writes to preallocated files.
The on-disk timestamps are updated only when:
- the inode needs to be updated for some change unrelated
to file timestamps
- the application employs fsync(2), syncfs(2), or sync(2)
- an undeleted inode is evicted from memory
- more than 24 hours have passed since the i-node was
written to disk.
nolazytime
Do not use the lazytime feature.
suid 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.
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 mounts.
The remount functionality follows the standard way the
mount command works with options from fstab. This means
that mount does not read fstab (or mtab) only when both
device and dir are specified.
mount -o remount,rw /dev/foo /dir
After this call all old mount options are replaced and
arbitrary stuff from fstab (or mtab) is ignored, except
the loop= option which is internally generated and
maintained by the mount command.
mount -o remount,rw /dir
After this call, mount reads fstab and merges these
options with the options from the command line (-o). If
no mountpoint is found in fstab, then a remount with
unspecified source is allowed.
mount allows the use of --all to remount all already
mounted filesystems which match a specified filter (-O and
-t). For example:
mount --all -o remount,ro -t vfat
remounts all already mounted vfat filesystems in read-only
mode. Each of the filesystems is remounted by "mount -o
remount,ro /dir" semantic. This means the mount command
reads fstab or mtab and merges these options with the
options from the command line.
ro Mount the filesystem read-only.
rw Mount the filesystem read-write.
sync All I/O to the filesystem should be done synchronously.
In the case of media with a limited number of write cycles
(e.g. some flash drives), sync may cause life-cycle
shortening.
user Allow an ordinary user to mount the filesystem. The name
of the mounting user is written to the mtab file (or to
the private libmount file in /run/mount on systems without
a regular mtab) so that this same user can unmount the
filesystem again. This option implies the options noexec,
nosuid, and nodev (unless overridden by subsequent
options, as in the option line user,exec,dev,suid).
nouser Forbid an ordinary user to mount the filesystem. This is
the default; it does not imply any other options.
users Allow any user to mount and to unmount the filesystem,
even when some other ordinary user mounted it. This
option implies the options noexec, nosuid, and nodev
(unless overridden by subsequent options, as in the option
line users,exec,dev,suid).
X-* All options prefixed with "X-" are interpreted as comments
or as userspace application-specific options. These
options are not stored in user space (e.g., mtab file),
nor sent to the mount.type helpers nor to the mount(2)
system call. The suggested format is X-appname.option.
x-* The same as X-* options, but stored permanently in user
space. This means the options are also available for
umount or other operations. Note that maintaining mount
options in user space is tricky, because it's necessary
use libmount-based tools and there is no guarantee that
the options will be always available (for example after a
move mount operation or in unshared namespace).
Note that before util-linux v2.30 the x-* options have not
been maintained by libmount and stored in user space
(functionality was the same as for X-* now), but due to
the growing number of use-cases (in initrd, systemd etc.)
the functionality has been extended to keep existing fstab
configurations usable without a change.
X-mount.mkdir[=mode]
Allow to make a target directory (mountpoint) if it does
not exit 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 executed
without suid permissions. The option is also supported as
x-mount.mkdir, this notation is deprecated since v2.30.
nosymfollow
Do not follow symlinks when resolving paths. Symlinks can
still be created, and readlink(1), readlink(2),
realpath(1) and realpath(3) all still work properly.
This section lists options that are specific to particular
filesystems. Where possible, you should first consult
filesystem-specific manual pages for details. Some of those
pages are listed in the following table.
Filesystem(s) Manual page
btrfs btrfs(5)
cifs mount.cifs(8)
ext2, ext3, ext4 ext4(5)
fuse fuse(8)
nfs nfs(5)
tmpfs tmpfs(5)
xfs xfs(5)
Note that some of the pages listed above might be available only
after you install the respective userland tools.
The following options apply only to certain filesystems. We sort
them by filesystem. All options follow the -o flag.
What options are supported depends a bit on the running kernel.
Further information may be available in filesystem-specific files
in the kernel source subdirectory Documentation/filesystems.
Mount options for adfs
uid=value and gid=value
Set the owner and group of the files in the filesystem
(default: uid=gid=0).
ownmask=value and othmask=value
Set the permission mask for ADFS 'owner' permissions and
'other' permissions, respectively (default: 0700 and 0077,
respectively). See also
/usr/src/linux/Documentation/filesystems/adfs.rst.
Mount options for affs
uid=value and gid=value
Set the owner and group of the root of the filesystem
(default: uid=gid=0, but with option uid or gid without
specified value, the UID and GID of the current process
are taken).
setuid=value and setgid=value
Set the owner and group of all files.
mode=value
Set the mode of all files to value & 0777 disregarding the
original permissions. Add search permission to
directories that have read permission. The value is given
in octal.
protect
Do not allow any changes to the protection bits on the
filesystem.
usemp Set UID and GID of the root of the filesystem to the UID
and GID of the mount point upon the first sync or umount,
and then clear this option. Strange...
verbose
Print an informational message for each successful mount.
prefix=string
Prefix used before volume name, when following a link.
volume=string
Prefix (of length at most 30) used before '/' when
following a symbolic link.
reserved=value
(Default: 2.) Number of unused blocks at the start of the
device.
root=value
Give explicitly the location of the root block.
bs=value
Give blocksize. Allowed values are 512, 1024, 2048, 4096.
grpquota|noquota|quota|usrquota
These options are accepted but ignored. (However, quota
utilities may react to such strings in /etc/fstab.)
Mount options for debugfs
The debugfs filesystem is a pseudo filesystem, traditionally
mounted on /sys/kernel/debug. As of kernel version 3.4, debugfs
has the following options:
uid=n, gid=n
Set the owner and group of the mountpoint.
mode=value
Sets the mode of the mountpoint.
Mount options for devpts
The devpts filesystem is a pseudo filesystem, traditionally
mounted on /dev/pts. In order to acquire a pseudo terminal, a
process opens /dev/ptmx; the number of the pseudo terminal is
then made available to the process and the pseudo terminal slave
can be accessed as /dev/pts/<number>.
uid=value and gid=value
This sets the owner or the group of newly created pseudo
terminals to the specified values. When nothing is
specified, they will be set to the UID and GID of the
creating process. For example, if there is a tty group
with GID 5, then gid=5 will cause newly created pseudo
terminals to belong to the tty group.
mode=value
Set the mode of newly created pseudo terminals to the
specified value. The default is 0600. A value of
mode=620 and gid=5 makes "mesg y" the default on newly
created pseudo terminals.
newinstance
Create a private instance of the devpts filesystem, such
that indices of pseudo terminals allocated in this new
instance are independent of indices created in other
instances of devpts.
All mounts of devpts without this newinstance option share
the same set of pseudo terminal indices (i.e., legacy
mode). Each mount of devpts with the newinstance option
has a private set of pseudo terminal indices.
This option is mainly used to support containers in the
Linux kernel. It is implemented in Linux kernel versions
starting with 2.6.29. Further, this mount option is valid
only if CONFIG_DEVPTS_MULTIPLE_INSTANCES is enabled in the
kernel configuration.
To use this option effectively, /dev/ptmx must be a
symbolic link to pts/ptmx. See
Documentation/filesystems/devpts.txt in the Linux kernel
source tree for details.
ptmxmode=value
Set the mode for the new ptmx device node in the devpts
filesystem.
With the support for multiple instances of devpts (see
newinstance option above), each instance has a private
ptmx node in the root of the devpts filesystem (typically
/dev/pts/ptmx).
For compatibility with older versions of the kernel, the
default mode of the new ptmx node is 0000. ptmxmode=value
specifies a more useful mode for the ptmx node and is
highly recommended when the newinstance option is
specified.
This option is only implemented in Linux kernel versions
starting with 2.6.29. Further, this option is valid only
if CONFIG_DEVPTS_MULTIPLE_INSTANCES is enabled in the
kernel configuration.
Mount options for fat
(Note: fat is not a separate filesystem, but a common part of the
msdos, umsdos and vfat filesystems.)
blocksize={512|1024|2048}
Set blocksize (default 512). This option is obsolete.
uid=value and gid=value
Set the owner and group of all files. (Default: the UID
and GID of the current process.)
umask=value
Set the umask (the bitmask of the permissions that are not
present). The default is the umask of the current
process. The value is given in octal.
dmask=value
Set the umask applied to directories only. The default is
the umask of the current process. The value is given in
octal.
fmask=value
Set the umask applied to regular files only. The default
is the umask of the current process. The value is given
in octal.
allow_utime=value
This option controls the permission check of mtime/atime.
20 If current process is in group of file's group ID,
you can change timestamp.
2 Other users can change timestamp.
The default is set from `dmask' option. (If the directory
is writable, utime(2) is also allowed. I.e. ~dmask & 022)
Normally utime(2) checks that the current process is owner
of the file, or that it has the CAP_FOWNER capability.
But FAT filesystems don't have UID/GID on disk, so the
normal check is too inflexible. With this option you can
relax it.
check=value
Three different levels of pickiness can be chosen:
r[elaxed]
Upper and lower case are accepted and equivalent,
long name parts are truncated (e.g.
verylongname.foobar becomes verylong.foo), leading
and embedded spaces are accepted in each name part
(name and extension).
n[ormal]
Like "relaxed", but many special characters (*, ?,
<, spaces, etc.) are rejected. This is the
default.
s[trict]
Like "normal", but names that contain long parts or
special characters that are sometimes used on Linux
but are not accepted by MS-DOS (+, =, etc.) are
rejected.
codepage=value
Sets the codepage for converting to shortname characters
on FAT and VFAT filesystems. By default, codepage 437 is
used.
conv=mode
This option is obsolete and may fail or be ignored.
cvf_format=module
Forces the driver to use the CVF (Compressed Volume File)
module cvf_module instead of auto-detection. If the
kernel supports kmod, the cvf_format=xxx option also
controls on-demand CVF module loading. This option is
obsolete.
cvf_option=option
Option passed to the CVF module. This option is obsolete.
debug Turn on the debug flag. A version string and a list of
filesystem parameters will be printed (these data are also
printed if the parameters appear to be inconsistent).
discard
If set, causes discard/TRIM commands to be issued to the
block device when blocks are freed. This is useful for
SSD devices and sparse/thinly-provisioned LUNs.
dos1xfloppy
If set, use a fallback default BIOS Parameter Block
configuration, determined by backing device size. These
static parameters match defaults assumed by DOS 1.x for
160 kiB, 180 kiB, 320 kiB, and 360 kiB floppies and floppy
images.
errors={panic|continue|remount-ro}
Specify FAT behavior on critical errors: panic, continue
without doing anything, or remount the partition in read-
only mode (default behavior).
fat={12|16|32}
Specify a 12, 16 or 32 bit fat. This overrides the
automatic FAT type detection routine. Use with caution!
iocharset=value
Character set to use for converting between 8 bit
characters and 16 bit Unicode characters. The default is
iso8859-1. Long filenames are stored on disk in Unicode
format.
nfs={stale_rw|nostale_ro}
Enable this only if you want to export the FAT filesystem
over NFS.
stale_rw: This option maintains an index (cache) of
directory inodes which is used by the nfs-related code to
improve look-ups. Full file operations (read/write) over
NFS are supported but with cache eviction at NFS server,
this could result in spurious ESTALE errors.
nostale_ro: This option bases the inode number and file
handle on the on-disk location of a file in the FAT
directory entry. This ensures that ESTALE will not be
returned after a file is evicted from the inode cache.
However, it means that operations such as rename, create
and unlink could cause file handles that previously
pointed at one file to point at a different file,
potentially causing data corruption. For this reason,
this option also mounts the filesystem readonly.
To maintain backward compatibility, '-o nfs' is also
accepted, defaulting to stale_rw.
tz=UTC This option disables the conversion of timestamps between
local time (as used by Windows on FAT) and UTC (which
Linux uses internally). This is particularly useful when
mounting devices (like digital cameras) that are set to
UTC in order to avoid the pitfalls of local time.
time_offset=minutes
Set offset for conversion of timestamps from local time
used by FAT to UTC. I.e., minutes will be subtracted from
each timestamp to convert it to UTC used internally by
Linux. This is useful when the time zone set in the
kernel via settimeofday(2) is not the time zone used by
the filesystem. Note that this option still does not
provide correct time stamps in all cases in presence of
DST - time stamps in a different DST setting will be off
by one hour.
quiet Turn on the quiet flag. Attempts to chown or chmod files
do not return errors, although they fail. Use with
caution!
rodir FAT has the ATTR_RO (read-only) attribute. On Windows,
the ATTR_RO of the directory will just be ignored, and is
used only by applications as a flag (e.g. it's set for the
customized folder).
If you want to use ATTR_RO as read-only flag even for the
directory, set this option.
showexec
If set, the execute permission bits of the file will be
allowed only if the extension part of the name is .EXE,
.COM, or .BAT. Not set by default.
sys_immutable
If set, ATTR_SYS attribute on FAT is handled as IMMUTABLE
flag on Linux. Not set by default.
flush If set, the filesystem will try to flush to disk more
early than normal. Not set by default.
usefree
Use the "free clusters" value stored on FSINFO. It'll be
used to determine number of free clusters without scanning
disk. But it's not used by default, because recent
Windows don't update it correctly in some case. If you
are sure the "free clusters" on FSINFO is correct, by this
option you can avoid scanning disk.
dots, nodots, dotsOK=[yes|no]
Various misguided attempts to force Unix or DOS
conventions onto a FAT filesystem.
Mount options for hfs
creator=cccc, type=cccc
Set the creator/type values as shown by the MacOS finder
used for creating new files. Default values: '????'.
uid=n, gid=n
Set the owner and group of all files. (Default: the UID
and GID of the current process.)
dir_umask=n, file_umask=n, umask=n
Set the umask used for all directories, all regular files,
or all files and directories. Defaults to the umask of
the current process.
session=n
Select the CDROM session to mount. Defaults to leaving
that decision to the CDROM driver. This option will fail
with anything but a CDROM as underlying device.
part=n Select partition number n from the device. Only makes
sense for CDROMs. Defaults to not parsing the partition
table at all.
quiet Don't complain about invalid mount options.
Mount options for hpfs
uid=value and gid=value
Set the owner and group of all files. (Default: the UID
and GID of the current process.)
umask=value
Set the umask (the bitmask of the permissions that are not
present). The default is the umask of the current
process. The value is given in octal.
case={lower|asis}
Convert all files names to lower case, or leave them.
(Default: case=lower.)
conv=mode
This option is obsolete and may fail or being ignored.
nocheck
Do not abort mounting when certain consistency checks
fail.
Mount options for iso9660
ISO 9660 is a standard describing a filesystem structure to be
used on CD-ROMs. (This filesystem type is also seen on some DVDs.
See also the udf filesystem.)
Normal iso9660 filenames appear in an 8.3 format (i.e., DOS-like
restrictions on filename length), and in addition all characters
are in upper case. Also there is no field for file ownership,
protection, number of links, provision for block/character
devices, etc.
Rock Ridge is an extension to iso9660 that provides all of these
UNIX-like features. Basically there are extensions to each
directory record that supply all of the additional information,
and when Rock Ridge is in use, the filesystem is
indistinguishable from a normal UNIX filesystem (except that it
is read-only, of course).
norock Disable the use of Rock Ridge extensions, even if
available. Cf. map.
nojoliet
Disable the use of Microsoft Joliet extensions, even if
available. Cf. map.
check={r[elaxed]|s[trict]}
With check=relaxed, a filename is first converted to lower
case before doing the lookup. This is probably only
meaningful together with norock and map=normal. (Default:
check=strict.)
uid=value and gid=value
Give all files in the filesystem the indicated user or
group id, possibly overriding the information found in the
Rock Ridge extensions. (Default: uid=0,gid=0.)
map={n[ormal]|o[ff]|a[corn]}
For non-Rock Ridge volumes, normal name translation maps
upper to lower case ASCII, drops a trailing `;1', and
converts `;' to `.'. With map=off no name translation is
done. See norock. (Default: map=normal.) map=acorn is
like map=normal but also apply Acorn extensions if
present.
mode=value
For non-Rock Ridge volumes, give all files the indicated
mode. (Default: read and execute permission for
everybody.) Octal mode values require a leading 0.
unhide Also show hidden and associated files. (If the ordinary
files and the associated or hidden files have the same
filenames, this may make the ordinary files inaccessible.)
block={512|1024|2048}
Set the block size to the indicated value. (Default:
block=1024.)
conv=mode
This option is obsolete and may fail or being ignored.
cruft If the high byte of the file length contains other
garbage, set this mount option to ignore the high order
bits of the file length. This implies that a file cannot
be larger than 16 MB.
session=x
Select number of session on multisession CD.
sbsector=xxx
Session begins from sector xxx.
The following options are the same as for vfat and specifying
them only makes sense when using discs encoded using Microsoft's
Joliet extensions.
iocharset=value
Character set to use for converting 16 bit Unicode
characters on CD to 8 bit characters. The default is
iso8859-1.
utf8 Convert 16 bit Unicode characters on CD to UTF-8.
Mount options for jfs
iocharset=name
Character set to use for converting from Unicode to ASCII.
The default is to do no conversion. Use iocharset=utf8
for UTF8 translations. This requires CONFIG_NLS_UTF8 to
be set in the kernel .config file.
resize=value
Resize the volume to value blocks. JFS only supports
growing a volume, not shrinking it. This option is only
valid during a remount, when the volume is mounted read-
write. The resize keyword with no value will grow the
volume to the full size of the partition.
nointegrity
Do not write to the journal. The primary use of this
option is to allow for higher performance when restoring a
volume from backup media. The integrity of the volume is
not guaranteed if the system abnormally ends.
integrity
Default. Commit metadata changes to the journal. Use
this option to remount a volume where the nointegrity
option was previously specified in order to restore normal
behavior.
errors={continue|remount-ro|panic}
Define the behavior when an error is encountered. (Either
ignore errors and just mark the filesystem erroneous and
continue, or remount the filesystem read-only, or panic
and halt the system.)
noquota|quota|usrquota|grpquota
These options are accepted but ignored.
Mount options for msdos
See mount options for fat. If the msdos filesystem detects an
inconsistency, it reports an error and sets the file system read-
only. The filesystem can be made writable again by remounting
it.
Mount options for ncpfs
Just like nfs, the ncpfs implementation expects a binary argument
(a struct ncp_mount_data) to the mount system call. This
argument is constructed by ncpmount(8) and the current version of
mount (2.12) does not know anything about ncpfs.
Mount options for ntfs
iocharset=name
Character set to use when returning file names. Unlike
VFAT, NTFS suppresses names that contain nonconvertible
characters. Deprecated.
nls=name
New name for the option earlier called iocharset.
utf8 Use UTF-8 for converting file names.
uni_xlate={0|1|2}
For 0 (or `no' or `false'), do not use escape sequences
for unknown Unicode characters. For 1 (or `yes' or
`true') or 2, use vfat-style 4-byte escape sequences
starting with ":". Here 2 give a little-endian encoding
and 1 a byteswapped bigendian encoding.
posix=[0|1]
If enabled (posix=1), the filesystem distinguishes between
upper and lower case. The 8.3 alias names are presented
as hard links instead of being suppressed. This option is
obsolete.
uid=value, gid=value and umask=value
Set the file permission on the filesystem. The umask
value is given in octal. By default, the files are owned
by root and not readable by somebody else.
Mount options for overlay
Since Linux 3.18 the overlay pseudo filesystem implements a union
mount for other filesystems.
An overlay filesystem combines two filesystems - an upper
filesystem and a lower filesystem. When a name exists in both
filesystems, the object in the upper filesystem is visible while
the object in the lower filesystem is either hidden or, in the
case of directories, merged with the upper object.
The lower filesystem can be any filesystem supported by Linux and
does not need to be writable. The lower filesystem can even be
another overlayfs. The upper filesystem will normally be
writable and if it is it must support the creation of trusted.*
extended attributes, and must provide a valid d_type in readdir
responses, so NFS is not suitable.
A read-only overlay of two read-only filesystems may use any
filesystem type. The options lowerdir and upperdir are combined
into a merged directory by using:
mount -t overlay overlay \
-olowerdir=/lower,upperdir=/upper,workdir=/work /merged
lowerdir=directory
Any filesystem, does not need to be on a writable
filesystem.
upperdir=directory
The upperdir is normally on a writable filesystem.
workdir=directory
The workdir needs to be an empty directory on the same
filesystem as upperdir.
Mount options for reiserfs
Reiserfs is a journaling filesystem.
conv Instructs version 3.6 reiserfs software to mount a version
3.5 filesystem, using the 3.6 format for newly created
objects. This filesystem will no longer be compatible
with reiserfs 3.5 tools.
hash={rupasov|tea|r5|detect}
Choose which hash function reiserfs will use to find files
within directories.
rupasov
A hash invented by Yury Yu. Rupasov. It is fast
and preserves locality, mapping lexicographically
close file names to close hash values. This option
should not be used, as it causes a high probability
of hash collisions.
tea A Davis-Meyer function implemented by Jeremy
Fitzhardinge. It uses hash permuting bits in the
name. It gets high randomness and, therefore, low
probability of hash collisions at some CPU cost.
This may be used if EHASHCOLLISION errors are
experienced with the r5 hash.
r5 A modified version of the rupasov hash. It is used
by default and is the best choice unless the
filesystem has huge directories and unusual file-
name patterns.
detect Instructs mount to detect which hash function is in
use by examining the filesystem being mounted, and
to write this information into the reiserfs
superblock. This is only useful on the first mount
of an old format filesystem.
hashed_relocation
Tunes the block allocator. This may provide performance
improvements in some situations.
no_unhashed_relocation
Tunes the block allocator. This may provide performance
improvements in some situations.
noborder
Disable the border allocator algorithm invented by Yury
Yu. Rupasov. This may provide performance improvements in
some situations.
nolog Disable journaling. This will provide slight performance
improvements in some situations at the cost of losing
reiserfs's fast recovery from crashes. Even with this
option turned on, reiserfs still performs all journaling
operations, save for actual writes into its journaling
area. Implementation of nolog is a work in progress.
notail By default, reiserfs stores small files and `file tails'
directly into its tree. This confuses some utilities such
as LILO(8). This option is used to disable packing of
files into the tree.
replayonly
Replay the transactions which are in the journal, but do
not actually mount the filesystem. Mainly used by
reiserfsck.
resize=number
A remount option which permits online expansion of
reiserfs partitions. Instructs reiserfs to assume that
the device has number blocks. This option is designed for
use with devices which are under logical volume management
(LVM). There is a special resizer utility which can be
obtained from ftp://ftp.namesys.com/pub/reiserfsprogs.
user_xattr
Enable Extended User Attributes. See the attr(1) manual
page.
acl Enable POSIX Access Control Lists. See the acl(5) manual
page.
barrier=none / barrier=flush
This disables / enables the use of write barriers in the
journaling code. barrier=none disables, barrier=flush
enables (default). This also requires an IO stack which
can support barriers, and if reiserfs gets an error on a
barrier write, it will disable barriers again with a
warning. Write barriers enforce proper on-disk ordering
of journal commits, making volatile disk write caches safe
to use, at some performance penalty. If your disks are
battery-backed in one way or another, disabling barriers
may safely improve performance.
Mount options for ubifs
UBIFS is a flash filesystem which works on top of UBI volumes.
Note that atime is not supported and is always turned off.
The device name may be specified as
ubiX_Y UBI device number X, volume number Y
ubiY UBI device number 0, volume number Y
ubiX:NAME
UBI device number X, volume with name NAME
ubi:NAME
UBI device number 0, volume with name NAME
Alternative ! separator may be used instead of :.
The following mount options are available:
bulk_read
Enable bulk-read. VFS read-ahead is disabled because it
slows down the filesystem. Bulk-Read is an internal
optimization. Some flashes may read faster if the data
are read at one go, rather than at several read requests.
For example, OneNAND can do "read-while-load" if it reads
more than one NAND page.
no_bulk_read
Do not bulk-read. This is the default.
chk_data_crc
Check data CRC-32 checksums. This is the default.
no_chk_data_crc.
Do not check data CRC-32 checksums. With this option, the
filesystem does not check CRC-32 checksum for data, but it
does check it for the internal indexing information. This
option only affects reading, not writing. CRC-32 is
always calculated when writing the data.
compr={none|lzo|zlib}
Select the default compressor which is used when new files
are written. It is still possible to read compressed
files if mounted with the none option.
Mount options for udf
UDF is the "Universal Disk Format" filesystem defined by OSTA,
the Optical Storage Technology Association, and is often used for
DVD-ROM, frequently in the form of a hybrid UDF/ISO-9660
filesystem. It is, however, perfectly usable by itself on disk
drives, flash drives and other block devices. See also iso9660.
uid= Make all files in the filesystem belong to the given user.
uid=forget can be specified independently of (or usually
in addition to) uid=<user> and results in UDF not storing
uids to the media. In fact the recorded uid is the 32-bit
overflow uid -1 as defined by the UDF standard. The value
is given as either <user> which is a valid user name or
the corresponding decimal user id, or the special string
"forget".
gid= Make all files in the filesystem belong to the given
group. gid=forget can be specified independently of (or
usually in addition to) gid=<group> and results in UDF not
storing gids to the media. In fact the recorded gid is the
32-bit overflow gid -1 as defined by the UDF standard.
The value is given as either <group> which is a valid
group name or the corresponding decimal group id, or the
special string "forget".
umask= Mask out the given permissions from all inodes read from
the filesystem. The value is given in octal.
mode= If mode= is set the permissions of all non-directory
inodes read from the filesystem will be set to the given
mode. The value is given in octal.
dmode= If dmode= is set the permissions of all directory inodes
read from the filesystem will be set to the given dmode.
The value is given in octal.
bs= Set the block size. Default value prior to kernel version
2.6.30 was 2048. Since 2.6.30 and prior to 4.11 it was
logical device block size with fallback to 2048. Since
4.11 it is logical block size with fallback to any valid
block size between logical device block size and 4096.
For other details see the mkudffs(8) 2.0+ manpage,
sections COMPATIBILITY and BLOCK SIZE.
unhide Show otherwise hidden files.
undelete
Show deleted files in lists.
adinicb
Embed data in the inode. (default)
noadinicb
Don't embed data in the inode.
shortad
Use short UDF address descriptors.
longad Use long UDF address descriptors. (default)
nostrict
Unset strict conformance.
iocharset=
Set the NLS character set. This requires kernel compiled
with CONFIG_UDF_NLS option.
utf8 Set the UTF-8 character set.
Mount options for debugging and disaster recovery
novrs Ignore the Volume Recognition Sequence and attempt to
mount anyway.
session=
Select the session number for multi-session recorded
optical media. (default= last session)
anchor=
Override standard anchor location. (default= 256)
lastblock=
Set the last block of the filesystem.
Unused historical mount options that may be encountered and should be
removed
uid=ignore
Ignored, use uid=<user> instead.
gid=ignore
Ignored, use gid=<group> instead.
volume=
Unimplemented and ignored.
partition=
Unimplemented and ignored.
fileset=
Unimplemented and ignored.
rootdir=
Unimplemented and ignored.
Mount options for ufs
ufstype=value
UFS is a filesystem widely used in different operating
systems. The problem are differences among
implementations. Features of some implementations are
undocumented, so its hard to recognize the type of ufs
automatically. That's why the user must specify the type
of ufs by mount option. Possible values are:
old Old format of ufs, this is the default, read only.
(Don't forget to give the -r option.)
44bsd For filesystems created by a BSD-like system
(NetBSD, FreeBSD, OpenBSD).
ufs2 Used in FreeBSD 5.x supported as read-write.
5xbsd Synonym for ufs2.
sun For filesystems created by SunOS or Solaris on
Sparc.
sunx86 For filesystems created by Solaris on x86.
hp For filesystems created by HP-UX, read-only.
nextstep
For filesystems created by NeXTStep (on NeXT
station) (currently read only).
nextstep-cd
For NextStep CDROMs (block_size == 2048), read-
only.
openstep
For filesystems created by OpenStep (currently read
only). The same filesystem type is also used by
Mac OS X.
onerror=value
Set behavior on error:
panic If an error is encountered, cause a kernel panic.
[lock|umount|repair]
These mount options don't do anything at present;
when an error is encountered only a console message
is printed.
Mount options for umsdos
See mount options for msdos. The dotsOK option is explicitly
killed by umsdos.
Mount options for vfat
First of all, the mount options for fat are recognized. The
dotsOK option is explicitly killed by vfat. Furthermore, there
are
uni_xlate
Translate unhandled Unicode characters to special escaped
sequences. This lets you backup and restore filenames
that are created with any Unicode characters. Without
this option, a '?' is used when no translation is
possible. The escape character is ':' because it is
otherwise invalid on the vfat filesystem. The escape
sequence that gets used, where u is the Unicode character,
is: ':', (u & 0x3f), ((u>>6) & 0x3f), (u>>12).
posix Allow two files with names that only differ in case. This
option is obsolete.
nonumtail
First try to make a short name without sequence number,
before trying name~num.ext.
utf8 UTF8 is the filesystem safe 8-bit encoding of Unicode that
is used by the console. It can be enabled for the
filesystem with this option or disabled with utf8=0,
utf8=no or utf8=false. If `uni_xlate' gets set, UTF8 gets
disabled.
shortname=mode
Defines the behavior for creation and display of filenames
which fit into 8.3 characters. If a long name for a file
exists, it will always be the preferred one for display.
There are four modes:
lower Force the short name to lower case upon display;
store a long name when the short name is not all
upper case.
win95 Force the short name to upper case upon display;
store a long name when the short name is not all
upper case.
winnt Display the short name as is; store a long name
when the short name is not all lower case or all
upper case.
mixed Display the short name as is; store a long name
when the short name is not all upper case. This
mode is the default since Linux 2.6.32.
Mount options for usbfs
devuid=uid and devgid=gid and devmode=mode
Set the owner and group and mode of the device files in
the usbfs filesystem (default: uid=gid=0, mode=0644). The
mode is given in octal.
busuid=uid and busgid=gid and busmode=mode
Set the owner and group and mode of the bus directories in
the usbfs filesystem (default: uid=gid=0, mode=0555). The
mode is given in octal.
listuid=uid and listgid=gid and listmode=mode
Set the owner and group and mode of the file devices
(default: uid=gid=0, mode=0444). The mode is given in
octal.
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 on the device filesystem is mounted.
Requires libcryptsetup with in libmount (optionally via dlopen).
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 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.
Supported since util-linux v2.35.
For example commands:
mksquashfs /etc /tmp/etc.squashfs
dd if=/dev/zero of=/tmp/etc.hash bs=1M count=10
veritysetup format /tmp/etc.squashfs /tmp/etc.hash
openssl smime -sign -in <hash> -nocerts -inkey private.key \
-signer private.crt -noattr -binary -outform der -out /tmp/etc.p7
mount -o verity.hashdevice=/tmp/etc.hash,verity.roothash=<hash>,\
verity.roothashsig=/tmp/etc.p7 /tmp/etc.squashfs /mnt
create squashfs image from /etc directory, verity hash device and
mount verified filesystem image to /mnt. The kernel will verify
that the root hash is signed by a key from the kernel keyring if
roothashsig is used.
One further possible type is a mount via the loop device. For
example, the command
mount /tmp/disk.img /mnt -t vfat -o loop=/dev/loop3
will set up the loop device /dev/loop3 to correspond to the file
/tmp/disk.img, and then mount this device on /mnt.
If no explicit loop device is mentioned (but just an option `-o
loop' is given), then mount will try to find some unused loop
device and use that, for example
mount /tmp/disk.img /mnt -o loop
The mount command automatically creates a loop device from a
regular file if a filesystem type is not specified or the
filesystem is known for libblkid, for example:
mount /tmp/disk.img /mnt
mount -t ext4 /tmp/disk.img /mnt
This type of mount knows about three options, namely loop, offset
and sizelimit, that are really options to losetup(8). (These
options can be used in addition to those specific to the
filesystem type.)
Since Linux 2.6.25 auto-destruction of loop devices is supported,
meaning that any loop device allocated by mount will be freed by
umount independently of /etc/mtab.
You can also free a loop device by hand, using losetup -d or
umount -d.
Since util-linux v2.29, mount re-uses the loop device rather than
initializing a new device if the same backing file is already
used for some loop device with the same offset and sizelimit.
This is necessary to avoid a filesystem corruption.
mount has the following exit status values (the bits can be
ORed):
0 success
1 incorrect invocation or permissions
2 system error (out of memory, cannot fork, no more loop
devices)
4 internal mount bug
8 user interrupt
16 problems writing or locking /etc/mtab
32 mount failure
64 some mount succeeded
The command mount -a returns 0 (all succeeded), 32 (all
failed), or 64 (some failed, some succeeded).
The syntax of external mount helpers is:
/sbin/mount.suffix spec dir [-sfnv] [-N namespace] [-o
options] [-t type.subtype]
where the suffix is the filesystem type and the -sfnvoN options
have the same meaning as the normal mount options. The -t option
is used for filesystems with subtypes support (for example
/sbin/mount.fuse -t fuse.sshfs).
The command mount does not pass the mount options unbindable,
runbindable, private, rprivate, slave, rslave, shared, rshared,
auto, noauto, comment, x-*, loop, offset and sizelimit to the
mount.<suffix> helpers. All other options are used in a comma-
separated list as an argument to the -o option.
LIBMOUNT_FSTAB=<path>
overrides the default location of the fstab file (ignored
for suid)
LIBMOUNT_MTAB=<path>
overrides the default location of the mtab file (ignored
for suid)
LIBMOUNT_DEBUG=all
enables libmount debug output
LIBBLKID_DEBUG=all
enables libblkid debug output
LOOPDEV_DEBUG=all
enables loop device setup debug output
See also "The files /etc/fstab, /etc/mtab and /proc/mounts"
section above.
/etc/fstab
filesystem table
/run/mount
libmount private runtime directory
/etc/mtab
table of mounted filesystems or symlink to /proc/mounts
/etc/mtab~
lock file (unused on systems with mtab symlink)
/etc/mtab.tmp
temporary file (unused on systems with mtab symlink)
/etc/filesystems
a list of filesystem types to try
A mount command existed in Version 5 AT&T UNIX.
It is possible for a corrupted filesystem to cause a crash.
Some Linux filesystems don't support -o sync and -o dirsync (the
ext2, ext3, ext4, fat and vfat filesystems do support synchronous
updates (a la BSD) when mounted with the sync option).
The -o remount may not be able to change mount parameters (all
ext2fs-specific parameters, except sb, are changeable with a
remount, for example, but you can't change gid or umask for the
fatfs).
It is possible that the files /etc/mtab and /proc/mounts don't
match on systems with a regular mtab file. The first file is
based only on the mount command options, but the content of the
second file also depends on the kernel and others settings (e.g.
on a remote NFS server -- in certain cases the mount command may
report unreliable information about an NFS mount point and the
/proc/mount file usually contains more reliable information.)
This is another reason to replace the mtab file with a symlink to
the /proc/mounts file.
Checking files on NFS filesystems referenced by file descriptors
(i.e. the fcntl and ioctl families of functions) may lead to
inconsistent results due to the lack of a consistency check in
the kernel even if the noac mount option is used.
The loop option with the offset or sizelimit options used may
fail when using older kernels if the mount command can't confirm
that the size of the block device has been configured as
requested. This situation can be worked around by using the
losetup command manually before calling mount with the configured
loop device.
Karel Zak <kzak@redhat.com>
lsblk(1), mount(2), umount(2), filesystems(5), fstab(5), nfs(5),
xfs(5), mount_namespaces(7) xattr(7) e2label(8), findmnt(8),
losetup(8), mke2fs(8), mountd(8), nfsd(8), swapon(8), tune2fs(8),
umount(8), xfs_admin(8)
The mount command is part of the util-linux package and is
available from
https://www.kernel.org/pub/linux/utils/util-linux/.
This page is part of the util-linux (a random collection of Linux
utilities) project. Information about the project can be found
at ⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩. If you
have a bug report for this manual page, send it to
util-linux@vger.kernel.org. This page was obtained from the
project's upstream Git repository
⟨git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git⟩ on
2020-12-18. (At that time, the date of the most recent commit
that was found in the repository was 2020-12-17.) If you
discover any rendering problems in this HTML version of the page,
or you believe there is a better or more up-to-date source for
the page, or you have corrections or improvements to the
information in this COLOPHON (which is not part of the original
manual page), send a mail to man-pages@man7.org
util-linux August 2015 MOUNT(8)
Pages that refer to this page: eject(1), fusermount3(1), homectl(1), mountpoint(1), quotasync(1), systemd-mount(1), unshare(1), chown(2), fcntl(2), fsync(2), ioctl_iflags(2), mount(2), open(2), open_by_handle_at(2), umount(2), getmntent(3), getsubopt(3), fd(4), hd(4), loop(4), ram(4), autofs(5), ext4(5), filesystems(5), fstab(5), lxc.container.conf(5), namespace.conf(5), nfs(5), nfsmount.conf(5), proc(5), systemd.automount(5), systemd.exec(5), systemd.mount(5), tmpfs(5), xfs(5), bootparam(7), fanotify(7), file-hierarchy(7), hier(7), inode(7), man-pages(7), mount_namespaces(7), automount(8), btrfs-subvolume(8), e4crypt(8), e4defrag(8), findmnt(8), fsck.cramfs(8), fsck.xfs(8), fsfreeze(8), fstrim(8), lsof(8), mkfs.cramfs(8), mkfs.xfs(8), mount(8), mount.fuse3(8), mount.nfs(8), pam_namespace(8), pivot_root(8), quotaon(8), swapon(8), switch_root(8), systemd-remount-fs.service(8), tune2fs(8), umount(8), wipefs(8), xfs_admin(8), xfs_db(8), xfs_freeze(8), xfs_growfs(8), xfs_info(8), xfs_logprint(8), xfs_rtcp(8)
|
HTML rendering created 2020-12-21 by Michael Kerrisk, author of The Linux Programming Interface, maintainer of the Linux man-pages project. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|