mount(8) — Linux manual page


MOUNT(8)                  System Administration                 MOUNT(8)

NAME         top

       mount - mount a filesystem

SYNOPSIS         top

       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


DESCRIPTION         top

       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

   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

              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

       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):

                     Human readable filesystem identifier. See also -L.

                     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.

                     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

                     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

              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

       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

       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

       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

       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

       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

       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

              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

              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

       -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

       -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

       -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

              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

              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-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

       --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.

              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

       --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-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

              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 '' 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

              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

              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

              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
              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

              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 \

              For more details, see selinux(8).

              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

       nodev  Do not interpret character or block special devices on the

              Update directory inode access times on this filesystem.
              This is the default.  (This option is ignored when noatime
              is set.)

              Do not update directory inode access times on this
              filesystem.  (This option is implied when noatime is set.)

              All directory updates within the filesystem should be done
              synchronously.  This affects the following system calls:
              creat, link, unlink, symlink, mkdir, rmdir, mknod and

       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

              Every time the inode is modified, the i_version field will
              be incremented.

              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.

              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.

              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.

              Do not use the relatime feature.  See also the strictatime
              mount option.

              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

              Use the kernel's default behavior for inode access time

              Only update times (atime, mtime, ctime) on the in-memory
              version of the file inode.

              This mount option significantly reduces writes to the
              inode table for workloads that perform frequent random
              writes to preallocated files.

              The on-disk timestamps are updated only when:

              - the inode needs to be updated for some change unrelated
                to file timestamps

              - the application employs fsync(2), syncfs(2), or sync(2)

              - an undeleted inode is evicted from memory

              - more than 24 hours have passed since the inode was
                written to disk.

              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).

              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

       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.

              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.

              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

   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.

              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.

              Do not allow any changes to the protection bits on the

       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...

              Print an informational message for each successful mount.

              Prefix used before volume name, when following a link.

              Prefix (of length at most 30) used before '/' when
              following a symbolic link.

              (Default: 2.) Number of unused blocks at the start of the

              Give explicitly the location of the root block.

              Give blocksize.  Allowed values are 512, 1024, 2048, 4096.

              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.

              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.

              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.

              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.


              Set the mode for the new ptmx device node in the devpts

              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

              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

              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.)

              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.)

              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.

              Set the umask applied to directories only.  The default is
              the umask of the current process.  The value is given in

              Set the umask applied to regular files only.  The default
              is the umask of the current process.  The value is given
              in octal.

              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.

              Three different levels of pickiness can be chosen:

                     Upper and lower case are accepted and equivalent,
                     long name parts are truncated (e.g.
                     verylongname.foobar becomes, leading
                     and embedded spaces are accepted in each name part
                     (name and extension).

                     Like "relaxed", but many special characters (*, ?,
                     <, spaces, etc.) are rejected.  This is the

                     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

              Sets the codepage for converting to shortname characters
              on FAT and VFAT filesystems.  By default, codepage 437 is

              This option is obsolete and may fail or be ignored.

              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

              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).

              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.

              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

              Specify FAT behavior on critical errors: panic, continue
              without doing anything, or remount the partition in read-
              only mode (default behavior).

              Specify a 12, 16 or 32 bit fat.  This overrides the
              automatic FAT type detection routine.  Use with caution!

              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

              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.

              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

       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.

              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.

              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.

              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.

              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.)

              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.

              Convert all files names to lower case, or leave them.
              (Default: case=lower.)

              This option is obsolete and may fail or being ignored.

              Do not abort mounting when certain consistency checks

   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.

              Disable the use of Microsoft Joliet extensions, even if
              available.  Cf. map.

              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:

       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.)

              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

              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.)

              Set the block size to the indicated value.  (Default:

              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.

              Select number of session on multisession CD.

              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.

              Character set to use for converting 16 bit Unicode
              characters on CD to 8 bit characters.  The default is

       utf8   Convert 16 bit Unicode characters on CD to UTF-8.

   Mount options for jfs
              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 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.

              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.

              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

              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.)

              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

   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
              Character set to use when returning file names.  Unlike
              VFAT, NTFS suppresses names that contain nonconvertible
              characters.  Deprecated.

              New name for the option earlier called iocharset.

       utf8   Use UTF-8 for converting file names.

              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.

              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

       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

              Any filesystem, does not need to be on a writable

              The upperdir is normally on a writable filesystem.

              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.

              Choose which hash function reiserfs will use to find files
              within directories.

                     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.

              Tunes the block allocator.  This may provide performance
              improvements in some situations.

              Tunes the block allocator.  This may provide performance
              improvements in some situations.

              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.

              Replay the transactions which are in the journal, but do
              not actually mount the filesystem.  Mainly used by

              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

              Enable Extended User Attributes.  See the attr(1) manual

       acl    Enable POSIX Access Control Lists.  See the acl(5) manual

       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

                     UBI device number X, volume with name NAME

                     UBI device number 0, volume with name NAME

       Alternative !  separator may be used instead of :.

       The following mount options are available:

              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.

              Do not bulk-read.  This is the default.

              Check data CRC-32 checksums.  This is the default.

              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.

              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

       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.

              Show deleted files in lists.

              Embed data in the inode. (default)

              Don't embed data in the inode.

              Use short UDF address descriptors.

       longad Use long UDF address descriptors. (default)

              Unset strict conformance.

              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.

              Select the session number for multi-session recorded
              optical media. (default= last session)

              Override standard anchor location. (default= 256)

              Set the last block of the filesystem.

   Unused historical mount options that may be encountered and should be
              Ignored, use uid=<user> instead.

              Ignored, use gid=<group> instead.

              Unimplemented and ignored.

              Unimplemented and ignored.

              Unimplemented and ignored.

              Unimplemented and ignored.

   Mount options for ufs
              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

              sunx86 For filesystems created by Solaris on x86.

              hp     For filesystems created by HP-UX, read-only.

                     For filesystems created by NeXTStep (on NeXT
                     station) (currently read only).

                     For NextStep CDROMs (block_size == 2048), read-

                     For filesystems created by OpenStep (currently read
                     only).  The same filesystem type is also used by
                     Mac OS X.

              Set behavior on error:

              panic  If an error is encountered, cause a kernel panic.

                     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

              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.

              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

              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

DM-VERITY SUPPORT (experimental)         top

       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:

              Path to the hash tree device associated with the source
              volume to pass to dm-verity.

              Hex-encoded hash of the root of verity.hashdevice Mutually
              exclusive with verity.roothashfile.

              Path to file containing the hex-encoded hash of the root
              of verity.hashdevice.  Mutually exclusive with

              If the hash tree device is embedded in the source volume,
              offset (default: 0) is used by dm-verity to get to the

              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.

              If the FEC device is embedded in the source volume, offset
              (default: 0) is used by dm-verity to get to the FEC area.

              Parity bytes for FEC (default: 2). Optional.

              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.

EXIT STATUS         top

       mount has the following exit status values (the bits can be

       0      success

       1      incorrect invocation or permissions

       2      system error (out of memory, cannot fork, no more loop

       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.

ENVIRONMENT         top

              overrides the default location of the fstab file (ignored
              for suid)

              overrides the default location of the mtab file (ignored
              for suid)

              enables libmount debug output

              enables libblkid debug output

              enables loop device setup debug output

FILES         top

       See also "The files /etc/fstab, /etc/mtab and /proc/mounts"
       section above.

              filesystem table

              libmount private runtime directory

              table of mounted filesystems or symlink to /proc/mounts

              lock file (unused on systems with mtab symlink)

              temporary file (unused on systems with mtab symlink)

              a list of filesystem types to try

HISTORY         top

       A mount command existed in Version 5 AT&T UNIX.

BUGS         top

       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

       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.

AUTHORS         top

       Karel Zak <>

SEE ALSO         top

       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)

AVAILABILITY         top

       The mount command is part of the util-linux package and is
       available from

COLOPHON         top

       This page is part of the util-linux (a random collection of Linux
       utilities) project.  Information about the project can be found
       at ⟨⟩.  If you
       have a bug report for this manual page, send it to  This page was obtained from the
       project's upstream Git repository
       ⟨git://⟩ on
       2021-03-21.  (At that time, the date of the most recent commit
       that was found in the repository was 2021-03-19.)  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

util-linux                     August 2015                      MOUNT(8)

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