MOUNT(8) System Administration MOUNT(8)
NAME
mount - mount a filesystem
SYNOPSIS
mount [-l|-h|-V]
mount -a [-fFnrsvw] [-t fstype] [-O optlist]
mount [-fnrsvw] [-o options] device|dir
mount [-fnrsvw] [-t fstype] [-o options] device dir
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 sev-
eral devices. The mount command serves to attach the filesystem found
on some device to the big file tree. Conversely, the umount(8) command
will detach it again. The filesystem is used to control how data is
stored on the device or provided in a virtual way by network or another
services.
The standard form of the mount command is:
mount -t type device dir
This tells the kernel to attach the filesystem found on device (which
is of type type) at the directory dir. The option -t type is optional.
The mount command is usually able to detect a filesystem. The root
permissions are necessary to mount a filesystem by default. See sec-
tion "Non-superuser mounts" below for more details. The previous con-
tents (if any) and owner and mode of dir become invisible, and as long
as this filesystem remains mounted, the pathname dir refers to the root
of the filesystem on device.
If only the directory or the device is given, for example:
mount /dir
then mount looks for a mountpoint (and if not found then for a device)
in the /etc/fstab file. It's possible to use the --target or --source
options to avoid ambivalent interpretation of the given argument. For
example:
mount --target /mountpoint
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 more times. The mount command does not implement any
policy to control this behavior. All behavior is controlled by the ker-
nel 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. It is
also possible to indicate a block special device using its filesystem
label or UUID (see the -L and -U options below), or its partition label
or UUID. Partition identifiers are supported for example for GUID Par-
tition Tables (GPT).
The device names of disk partitions are unstable; hardware reconfigura-
tion, 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.
The command lsblk --fs provides an overview of filesystems, LABELs and
UUIDs on available block devices. The command blkid -p <device> pro-
vides details about a filesystem on the specified device.
Don't forget that there is no guarantee that UUIDs and labels are re-
ally unique, especially if you move, share or copy the device. Use ls-
blk -o +UUID,PARTUUID to verify that the UUIDs are really unique in
your system.
The recommended setup is to use tags (e.g. UUID=uuid) rather than
/dev/disk/by-{label,uuid,partuuid,partlabel} udev symlinks in the
/etc/fstab file. Tags are more readable, robust and portable. The
mount(8) command internally uses udev symlinks, so the use of symlinks
in /etc/fstab has no advantage over tags. For more details see lib-
blkid(3).
Note that mount(8) uses UUIDs as strings. The UUIDs from the command
line or from fstab(5) are not converted to internal binary representa-
tion. The string representation of the UUID should be based on lower
case characters.
The proc filesystem is not associated with a special device, and when
mounting it, an arbitrary keyword, such as proc can be used instead of
a device specification. (The customary choice none is less fortunate:
the error message `none already mounted' from mount can be confusing.)
The files /etc/fstab, /etc/mtab and /proc/mounts
The file /etc/fstab (see fstab(5)), may contain lines describing what
devices are usually mounted where, using which options. The default
location of the fstab(5) file can be overridden with the --fstab path
command-line option (see below for more details).
The command
mount -a [-t type] [-O optlist]
(usually given in a bootscript) causes all filesystems mentioned in
fstab (of the proper type and/or having or not having the proper op-
tions) to be mounted as indicated, except for those whose line contains
the noauto keyword. Adding the -F option will make mount fork, so that
the filesystems are mounted simultaneously.
When mounting a filesystem mentioned in fstab or mtab, it suffices to
specify on the command line only the device, or only the mount point.
The programs mount and umount traditionally maintained a list of cur-
rently mounted filesystems in the file /etc/mtab. The support for reg-
ular classic /etc/mtab is completely disabled in compile time by de-
fault, because on current Linux systems it is better to make it a sym-
link 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 than
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 is possi-
ble to change by command line option --options-mode. The usual behav-
ior is that the last option wins if there are conflicting ones.
The mount program does not read the /etc/fstab file if both device (or
LABEL, UUID, PARTUUID or PARTLABEL) and dir are specified. For exam-
ple, to mount device foo at /dir:
mount /dev/foo /dir
This default behaviour is possible to change by command line option
--options-source-force to always read configuration from fstab. For
non-root users mount always read 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 corre-
sponding 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 spec-
ified on command line are verified before fstab is parsed or a helper
program is executed. It's strongly recommended to use a valid mount-
point to specify filesystem, otherwise mount may fail. For example it's
bad idea to use NFS or CIFS source on command line.
Since version 2.35 mount command does not exit when user permissions
are inadequate by internal libmount security rules. It drops suid per-
missions and continue as regular non-root user. It allows to support
use-cases where root permissions are not necessary (e.g., fuse filesys-
tems, user namespaces, etc).
For more details, see fstab(5). Only the user that mounted a filesys-
tem can unmount it again. If any user should be able to unmount it,
then use users instead of user in the fstab line. The owner option is
similar to the user option, with the restriction that the user must be
the owner of the special file. This may be useful e.g. for /dev/fd if
a login script makes the console user owner of this device. The group
option is similar, with the restriction that the user must be member of
the group of the special file.
Bind 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 to create any sec-
ond-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 "bind" operation. The olddir
and newdir are independent and the olddir may be umounted.
One can also remount a single file (on a single file). It's also pos-
sible to use the bind mount to create a mountpoint from a regular di-
rectory, for example:
mount --bind foo foo
The bind mount call attaches only (part of) a single filesystem, not
possible submounts. The entire file hierarchy including submounts is
attached a second place by using:
mount --rbind olddir newdir
Note that the filesystem mount options maintained by kernel will remain
the same as those on the original mount point. The userspace mount op-
tions (e.g., _netdev) will not be copied by mount(8) and it's necessary
explicitly specify the options on mount command line.
mount(8) since v2.27 allows to change the mount options by passing the
relevant options along with --bind. For example:
mount -o bind,ro foo foo
This feature is not supported by the Linux kernel; it is implemented in
userspace by an additional mount(2) remounting system call. This solu-
tion 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 en-
try), but the original filesystem superblock will still be writable,
meaning that the olddir will be writable, but the newdir will be read-
only.
It's also possible to change nosuid, nodev, noexec, noatime, nodiratime
and relatime VFS entry flags by "remount,bind" operation. The another
(for example filesystem specific flags) are silently ignored. It's im-
possible to change mount options recursively (for example with -o
rbind,ro).
mount(8) since v2.31 ignores the bind flag from /etc/fstab on remount
operation (if "-o remount" specified on command line). This is neces-
sary to fully control mount options on remount by command line. In the
previous versions the bind flag has been always applied and it was im-
possible to re-define mount options without interaction with the bind
semantic. This mount(8) behavior does not affect situations when "re-
mount,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 pri-
vate mount which cannot be cloned through a bind operation. The de-
tailed semantics are documented in Documentation/filesystems/sharedsub-
tree.txt file in the kernel source tree.
Supported operations are:
mount --make-shared mountpoint
mount --make-slave mountpoint
mount --make-private mountpoint
mount --make-unbindable mountpoint
The following commands allow one to recursively change the type of all
the mounts under a given mountpoint.
mount --make-rshared mountpoint
mount --make-rslave mountpoint
mount --make-rprivate mountpoint
mount --make-runbindable mountpoint
mount(8) does not read fstab(5) when a --make-* operation is requested.
All necessary information has to be specified on the command line.
Note that the Linux kernel does not allow to change multiple propaga-
tion flags with a single mount(2) system call, and the flags cannot be
mixed with other mount options and operations.
Since util-linux 2.23 the mount command allows to do more propagation
(topology) changes by one mount(8) call and do it also together with
other mount operations. This feature is EXPERIMENTAL. The propagation
flags are applied by additional mount(2) system calls when the preced-
ing 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 deter-
mined by first extracting the mount options for the filesystem from the
fstab table, then applying any options specified by the -o argument,
and finally applying a -r or -w option, when present.
The command mount does not pass all command-line options to the
/sbin/mount.suffix mount helpers. The interface between mount and the
mount helpers is described below in the section EXTERNAL HELPERS.
Command-line options available for the mount command are:
-a, --all
Mount all filesystems (of the given types) mentioned in fstab
(except for those whose line contains the noauto keyword). The
filesystems are mounted following their order in fstab. 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 dur-
ing mount --all. It 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 check-
ing. The recommended solution is findmnt --verify.
-B, --bind
Remount a subtree somewhere else (so that its contents are
available in both places). See above, under Bind mounts.
-c, --no-canonicalize
Don't canonicalize paths. The mount command canonicalizes all
paths (from command line or fstab) by default. This option can
be used together with the -f flag for already canonicalized ab-
solute paths. The option is designed for mount helpers which
call mount -i. It is strongly recommended to not use this com-
mand-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 de-
vices or different NFS servers in parallel. This has the advan-
tage that it is faster; also NFS timeouts go in parallel. A
disadvantage is that the mounts are done in undefined order.
Thus, you cannot use this option if you want to mount both /usr
and /usr/spool.
-f, --fake
Causes everything to be done except for the actual system call;
if it's not obvious, this ``fakes'' mounting the filesystem.
This option is useful in conjunction with the -v flag to deter-
mine 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 regu-
lar 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 reis-
erfs 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 exam-
ple when /etc is on a read-only filesystem.
-N, --namespace ns
Perform mount in 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 namespace when it reads /etc/fstab,
writes /etc/mtab (or writes to /run/mount) and calls mount(2)
system call, otherwise it runs in the original namespace. It
means that the target namespace does not have to contain any li-
braries or another requirements necessary to execute mount(2)
command.
See 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 _net-
dev 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 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 command line. Default value is
prepend -- it means command line options are evaluated after
fstab options. Note that the last option wins if there are con-
flicting ones.
--options-source source
Source of default options. source is comma separated list of
fstab, mtab and disable. disable disables fstab and mtab and
disables --options-source-force. 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 exam-
ple, 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 op-
tions 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 ar-
gument might be interpreted as target (mountpoint) or source
(device). This option allows to explicitly define that the ar-
gument is the mount source.
--target directory
If only one argument for the mount command is given then the ar-
gument might be interpreted as target (mountpoint) or source
(device). This option allows to explicitly define that the ar-
gument is the mount target.
--target-prefix directory
Prepend specified directory to all mount targets. This option
allows to follow fstab, but mount operations is done on another
place, for example:
mount --all --target-prefix /chroot -o X-mount.mkdir
mounts all from system fstab to /chroot, all missing muontpoint
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 ig-
nored. The option can be specified more than once. This option
is mostly designed for initramfs or chroot scripts where addi-
tional configuration is specified beyond standard system config-
uration.
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/mod-
ules/$(uname -r)/kernel/fs for a complete list of the filesys-
tems. 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#ex-
ample.com' is deprecated).
If no -t option is given, or if the auto type is specified,
mount will try to guess the desired type. Mount uses the blkid
library for guessing the filesystem type; if that does not turn
up anything that looks familiar, mount will try to read the file
/etc/filesystems, or, if that does not exist, /proc/filesystems.
All of the filesystem types listed there will be tried, except
for those that are labeled "nodev" (e.g. devpts, proc and nfs).
If /etc/filesystems ends in a line with a single *, mount will
read /proc/filesystems afterwards. While trying, all filesystem
types will be mounted with the mount option silent.
The auto type may be useful for user-mounted floppies. Creating
a file /etc/filesystems can be useful to change the probe order
(e.g., to try vfat before msdos or ext3 before ext2) or if you
use a kernel module autoloader.
More than one type may be specified in a comma-separated list,
for option -t as well as in an /etc/fstab entry. The list of
filesystem types for option -t can be prefixed with no to spec-
ify the filesystem types on which no action should be taken.
The prefix no has no effect when specified in an /etc/fstab en-
try.
The prefix no can be meaningful with the -a option. For exam-
ple, 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 filesys-
tem 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 pro-
gram. In order to make it possible to treat all types in a uni-
form way, mount will execute the program /sbin/mount.type (if
that exists) when called with type type. Since different ver-
sions of the smbmount program have different calling conven-
tions, /sbin/mount.smbfs may have to be a shell script that sets
up the desired call.
-U, --uuid uuid
Mount the partition that has the specified uuid.
-v, --verbose
Verbose mode.
-w, --rw, --read-write
Mount the filesystem read/write. The read-write is kernel de-
fault. A synonym is -o rw.
Note that specify -w on command line forces mount command to
never try read-only mount on write-protected devices. The de-
fault is try read-only if the previous mount syscall with read-
write flags failed.
-V, --version
Display version information and exit.
-h, --help
Display help text and exit.
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 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 con-
trolled 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 ear-
lier 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 filesys-
tem label is separate from the individual labels on the files.
It represents the entire filesystem for certain kinds of permis-
sion 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 con-
text that fscontext provides, in addition to supplying the same
label for individual files.
You can set the default security context for unlabeled files us-
ing defcontext= option. This overrides the value set for unla-
beled files in the policy and requires a filesystem that sup-
ports xattr labeling.
The rootcontext= option allows you to explicitly label the root
inode of a FS being mounted before that FS or inode becomes vis-
ible 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 con-
text.
Warning: the context value might contain commas, in which case
the value has to be properly quoted, otherwise mount(8) will in-
terpret the comma as a separator between mount options. Don't
forget that the shell strips off quotes and thus double quoting
is required. For example:
mount -t tmpfs none /mnt -o \
'context="system_u:object_r:tmp_t:s0:c127,c456",noexec'
For more details, see selinux(8).
defaults
Use the default options: rw, suid, dev, exec, auto, nouser, and
async.
Note that the real set of all default mount options depends on
kernel and filesystem type. See the beginning of this section
for more details.
dev Interpret character or block special devices on the filesystem.
nodev Do not interpret character or block special devices on the file
system.
diratime
Update directory inode access times on this filesystem. This is
the default. (This option is ignored when noatime is set.)
nodiratime
Do not update directory inode access times on this filesystem.
(This option is implied when noatime is set.)
dirsync
All directory updates within the filesystem should be done syn-
chronously. 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 im-
plies the options nosuid and nodev (unless overridden by subse-
quent 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 ear-
lier 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 ta-
ble for workloads that perform frequent random writes to preal-
located 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 capabili-
ties 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 com-
monly used to change the mount flags for a filesystem, espe-
cially to make a readonly filesystem writable. It does not
change device or mount point.
The remount operation together with the bind flag has special
semantic. See above, the subsection Bind mounts.
The remount functionality follows the standard way the mount
command works with options from fstab. This means that mount
does not read fstab (or mtab) only when both device and dir are
specified.
mount -o remount,rw /dev/foo /dir
After this call all old mount options are replaced and arbitrary
stuff from fstab (or mtab) is ignored, except the loop= option
which is internally generated and maintained by the mount com-
mand.
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 al-
lowed.
mount(8) allows to use --all to remount all already mounted
filesystems which match a specified filter (-O and -t). For ex-
ample:
mount --all -o remount,ro -t vfat
remounts all already mounted vfat filesystems in read-only mode.
The each of the filesystems is remounted by "mount -o remount,ro
/dir" semantic. It 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 subse-
quent options, as in the option line users,exec,dev,suid).
X-* All options prefixed with "X-" are interpreted as comments or as
userspace application-specific options. These options are not
stored in the user space (e.g., mtab file), nor sent to the
mount.type helpers nor to the mount(2) system call. The sug-
gested format is X-appname.option.
x-* The same as X-* options, but stored permanently in the user
space. It means the options are also available for umount or an-
other operations. Note that maintain mount options in user
space is tricky, because it's necessary use libmount based tools
and there is no guarantee that the options will be always avail-
able (for example after a move mount operation or in unshared
namespace).
Note that before util-linux v2.30 the x-* options have not been
maintained by libmount and stored in user space (functionality
was the same as have X-* now), but due to growing number of use-
cases (in initrd, systemd etc.) the functionality have been ex-
tended 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 op-
tion is also supported as x-mount.mkdir, this notation is depre-
cated since v2.30.
FILESYSTEM-SPECIFIC MOUNT OPTIONS
You should consult the respective man page for the filesystem first.
If you want to know what options the ext4 filesystem supports, then
check the ext4(5) man page. If that doesn't exist, you can also check
the corresponding mount page like mount.cifs(8). Note that you might
have to install the respective userland tools.
The following options apply only to certain filesystems. We sort them
by filesystem. They all follow the -o flag.
What options are supported depends a bit on the running kernel. More
info may be found in the kernel source subdirectory Documenta-
tion/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, respec-
tively). See also /usr/src/linux/Documentation/filesys-
tems/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 orig-
inal 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 filesys-
tem.
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 de-
vice.
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 utili-
ties may react to such strings in /etc/fstab.)
Mount options for debugfs
The debugfs filesystem is a pseudo filesystem, traditionally mounted on
/sys/kernel/debug. As of kernel version 3.4, debugfs has the following
options:
uid=n, gid=n
Set the owner and group of the mountpoint.
mode=value
Sets the mode of the mountpoint.
Mount options for devpts
The devpts filesystem is a pseudo filesystem, traditionally mounted on
/dev/pts. In order to acquire a pseudo terminal, a process opens
/dev/ptmx; the number of the pseudo terminal is then made available to
the process and the pseudo terminal slave can be accessed as
/dev/pts/<number>.
uid=value and gid=value
This sets the owner or the group of newly created PTYs to the
specified values. When nothing is specified, they will be set
to the UID and GID of the creating process. For example, if
there is a tty group with GID 5, then gid=5 will cause newly
created PTYs to belong to the tty group.
mode=value
Set the mode of newly created PTYs to the specified value. The
default is 0600. A value of mode=620 and gid=5 makes "mesg y"
the default on newly created PTYs.
newinstance
Create a private instance of devpts filesystem, such that in-
dices of ptys allocated in this new instance are independent of
indices created in other instances of devpts.
All mounts of devpts without this newinstance option share the
same set of pty indices (i.e., legacy mode). Each mount of de-
vpts with the newinstance option has a private set of pty in-
dices.
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 CON-
FIG_DEVPTS_MULTIPLE_INSTANCES is enabled in the kernel configu-
ration.
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 filesys-
tem.
With the support for multiple instances of devpts (see newin-
stance 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 start-
ing with 2.6.29. Further, this option is valid only if CON-
FIG_DEVPTS_MULTIPLE_INSTANCES is enabled in the kernel configu-
ration.
Mount options for fat
(Note: fat is not a separate filesystem, but a common part of the ms-
dos, umsdos and vfat filesystems.)
blocksize={512|1024|2048}
Set blocksize (default 512). This option is obsolete.
uid=value and gid=value
Set the owner and group of all files. (Default: the UID and GID
of the current process.)
umask=value
Set the umask (the bitmask of the permissions that are not
present). The default is the umask of the current process. The
value is given in octal.
dmask=value
Set the umask applied to directories only. The default is the
umask of the current process. The value is given in octal.
fmask=value
Set the umask applied to regular files only. The default is the
umask of the current process. The value is given in octal.
allow_utime=value
This option controls the permission check of mtime/atime.
20 If current process is in group of file's group ID, you
can change timestamp.
2 Other users can change timestamp.
The default is set from `dmask' option. (If the directory is
writable, utime(2) is also allowed. I.e. ~dmask & 022)
Normally utime(2) checks current process is owner of the file,
or it has CAP_FOWNER capability. But FAT filesystem doesn't
have UID/GID on disk, so normal check is too inflexible. With
this option you can relax it.
check=value
Three different levels of pickiness can be chosen:
r[elaxed]
Upper and lower case are accepted and equivalent, long
name parts are truncated (e.g. verylongname.foobar be-
comes verylong.foo), leading and embedded spaces are ac-
cepted 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 spe-
cial characters that are sometimes used on Linux but are
not accepted by MS-DOS (+, =, etc.) are rejected.
codepage=value
Sets the codepage for converting to shortname characters on FAT
and VFAT filesystems. By default, codepage 437 is used.
conv=mode
This option is obsolete and may fail or being ignored.
cvf_format=module
Forces the driver to use the CVF (Compressed Volume File) module
cvf_module instead of auto-detection. If the kernel supports
kmod, the cvf_format=xxx option also controls on-demand CVF mod-
ule 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 filesys-
tem 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 configura-
tion, determined by backing device size. These static parame-
ters 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 (de-
fault 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 spu-
rious 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, po-
tentially 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 in-
ternally). 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 time-
stamp 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 op-
tion 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 direc-
tory, 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 de-
cision 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 re-
strictions 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 filesys-
tem (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 avail-
able. 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 to-
gether 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 ex-
tensions. (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 exten-
sions.
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 key-
word 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 op-
tion to remount a volume where the nointegrity option was previ-
ously specified in order to restore normal behavior.
errors={continue|remount-ro|panic}
Define the behavior when an error is encountered. (Either ig-
nore errors and just mark the filesystem erroneous and continue,
or remount the filesystem read-only, or panic and halt the sys-
tem.)
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 incon-
sistency, 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 con-
structed 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 un-
known 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 en-
coding.
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 di-
rectory 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 filesys-
tem 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 pre-
serves 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 filesys-
tem.
hashed_relocation
Tunes the block allocator. This may provide performance im-
provements in some situations.
no_unhashed_relocation
Tunes the block allocator. This may provide performance im-
provements in some situations.
noborder
Disable the border allocator algorithm invented by Yury Yu. Ru-
pasov. This may provide performance improvements in some situa-
tions.
nolog Disable journaling. This will provide slight performance im-
provements 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 ac-
tual writes into its journaling area. Implementation of nolog
is a work in progress.
notail By default, reiserfs stores small files and `file tails' di-
rectly 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 ac-
tually mount the filesystem. Mainly used by reiserfsck.
resize=number
A remount option which permits online expansion of reiserfs par-
titions. Instructs reiserfs to assume that the device has num-
ber 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 jour-
naling code. barrier=none disables, barrier=flush enables (de-
fault). This also requires an IO stack which can support barri-
ers, 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 barri-
ers may safely improve performance.
Mount options for ubifs
UBIFS is a flash filesystem which works on top of UBI volumes. Note
that atime is not supported and is always turned off.
The device name may be specified as
ubiX_Y UBI device number X, volume number Y
ubiY UBI device number 0, volume number Y
ubiX:NAME
UBI device number X, volume with name NAME
ubi:NAME
UBI device number 0, volume with name NAME
Alternative ! separator may be used instead of :.
The following mount options are available:
bulk_read
Enable bulk-read. VFS read-ahead is disabled because it slows
down the file system. Bulk-Read is an internal optimization.
Some flashes may read faster if the data are read at one go,
rather than at several read requests. For example, OneNAND can
do "read-while-load" if it reads more than one NAND page.
no_bulk_read
Do not bulk-read. This is the default.
chk_data_crc
Check data CRC-32 checksums. This is the default.
no_chk_data_crc.
Do not check data CRC-32 checksums. With this option, the
filesystem does not check CRC-32 checksum for data, but it does
check it for the internal indexing information. This option
only affects reading, not writing. CRC-32 is always calculated
when writing the data.
compr={none|lzo|zlib}
Select the default compressor which is used when new files are
written. It is still possible to read compressed files if
mounted with the none option.
Mount options for udf
UDF is the "Universal Disk Format" filesystem defined by OSTA, the Op-
tical Storage Technology Association, and is often used for DVD-ROM,
frequently in the form of a hybrid UDF/ISO-9660 filesystem. It is, how-
ever, 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 ad-
dition 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 ad-
dition 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 de-
vice block size and 4096.
For other details see the mkudffs(8) 2.0+ manpage, sections COM-
PATIBILITY 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 any-
way.
session=
Select the session number for multi-session recorded optical me-
dia. (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 re-
moved
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 op-
tion is explicitly killed by vfat. Furthermore, there are
uni_xlate
Translate unhandled Unicode characters to special escaped se-
quences. 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 char-
acter, is: ':', (u & 0x3f), ((u>>6) & 0x3f), (u>>12).
posix Allow two files with names that only differ in case. This op-
tion 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 de-
fault 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 us-
bfs 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 (experimental)
The device-mapper verity target provides read-only transparent integ-
rity checking of block devices using kernel crypto API. The mount com-
mand can open the dm-verity device and do the integrity verification
before on the device filesystem is mounted. Requires libcryptsetup
with in libmount. 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 ex-
clusive with verity.roothashfile.
verity.roothashfile=path
Path to file containing the hex-encoded hash of the root of ver-
ity.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 (de-
fault: 0) is used by dm-verity to get to the FEC area. Optional.
verity.fecroots=value
Parity bytes for FEC (default: 2). 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
mount -o verity.hashdevice=/tmp/etc.hash,verity.roothash=<hash> /tmp/etc.squashfs /mnt
create squashfs image from /etc directory, verity hash device and mount
verified filesystem image to /mnt.
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, mean-
ing that any loop device allocated by mount will be freed by umount in-
dependently of /etc/mtab.
You can also free a loop device by hand, using losetup -d or umount -d.
Since util-linux v2.29 mount command re-uses the loop device rather
than initialize a new device if the same backing file is already used
for some loop device with the same offset and sizelimit. This is neces-
sary to avoid a filesystem corruption.
RETURN CODES
mount has the following return codes (the bits can be ORed):
0 success
1 incorrect invocation or permissions
2 system error (out of memory, cannot fork, no more loop devices)
4 internal mount bug
8 user interrupt
16 problems writing or locking /etc/mtab
32 mount failure
64 some mount succeeded
The command mount -a returns 0 (all succeeded), 32 (all failed),
or 64 (some failed, some succeeded).
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, runbind-
able, private, rprivate, slave, rslave, shared, rshared, auto, noauto,
comment, x-*, loop, offset and sizelimit to the mount.<suffix> helpers.
All other options are used in a comma-separated list as argument to the
-o option.
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
ENVIRONMENT
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
mount(2), umount(2), umount(8), fstab(5), nfs(5), xfs(5), e2label(8),
findmnt(8), losetup(8), mke2fs(8), mountd(8), nfsd(8), swapon(8),
tune2fs(8), xfs_admin(8)
BUGS
It is possible for a corrupted filesystem to cause a crash.
Some Linux filesystems don't support -o sync nor -o dirsync (the ext2,
ext3, 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 ex-
ample, but you can't change gid or umask for the fatfs).
It is possible that the files /etc/mtab and /proc/mounts don't match on
systems with a regular mtab file. The first file is based only on the
mount command options, but the content of the second file also depends
on the kernel and others settings (e.g. on a remote NFS server -- in
certain cases the mount command may report unreliable information about
an NFS mount point and the /proc/mounts file usually contains more re-
liable 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 re-
sults due to the lack of a consistency check in the kernel even if noac
is used.
The loop option with the offset or sizelimit options used may fail when
using older kernels if the mount command can't confirm that the size of
the block device has been configured as requested. This situation can
be worked around by using the losetup command manually before calling
mount with the configured loop device.
HISTORY
A mount command existed in Version 5 AT&T UNIX.
AUTHORS
Karel Zak <kzak@redhat.com>
AVAILABILITY
The mount command is part of the util-linux package and is available
from https://www.kernel.org/pub/linux/utils/util-linux/.
util-linux August 2015 MOUNT(8)