MOUNT(8)                      System Administration                     MOUNT(8)

       mount - mount a filesystem

       mount [-h|-V]

       mount [-l] [-t fstype]

       mount -a [-fFnrsvw] [-t fstype] [-O optlist]

       mount [-fnrsvw] [-o options] device|mountpoint

       mount [-fnrsvw] [-t fstype] [-o options] device mountpoint

       mount --bind|--rbind|--move olddir newdir


       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

              mount --target /mountpoint

       The same filesystem may be mounted more than once, and in some cases
       (e.g., network filesystems) the same filesystem may be mounted on the
       same mountpoint multiple times. The mount command does not implement any
       policy to control this behavior. All behavior is controlled by the kernel
       and it is usually specific to the filesystem driver. The exception is
       --all, in this case already mounted filesystems are ignored (see --all
       below for more details).

   Listing the mounts
       The listing mode is maintained for backward compatibility only.

       For more robust and customizable output use findmnt(8), especially in
       your scripts.  Note that control characters in the mountpoint name are
       replaced with '?'.

       The following command lists all mounted filesystems (of type type):

              mount [-l] [-t type]

       The option -l adds labels to this listing.  See below.

   Indicating the device and filesystem
       Most devices are indicated by a filename (of a block special device),
       like /dev/sda1, but there are other possibilities.  For example, in the
       case of an NFS mount, device may look like

       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 (GPT).

                     Partition universally unique identifier.  This identifier
                     is independent on filesystem and does not change by mkfs or
                     mkswap operations  It's supported for example for GUID
                     Partition Tables (GPT).

              ID=id  Hardware block device ID as generated by udevd.  This
                     identifier is usually based on WWN (unique storage
                     identifier) and assigned by the hardware manufacturer.  See
                     ls /dev/disk/by-id for more details, this directory and
                     running udevd is required.  This identifier is not
                     recommended for generic use as the identifier is not
                     strictly defined and it depends on udev, udev rules and

       The command lsblk --fs provides an overview of filesystems, LABELs and
       UUIDs on available block devices.  The command blkid -p <device> provides
       details about a filesystem on the specified device.

       Don't forget that there is no guarantee that UUIDs and labels are really
       unique, especially if you move, share or copy the device.  Use lsblk -o
       +UUID,PARTUUID to verify that the UUIDs are really unique in your system.

       The recommended setup is to use tags (e.g. UUID=uuid) rather than
       /dev/disk/by-{label,uuid,id,partuuid,partlabel} udev symlinks in the
       /etc/fstab file.  Tags are more readable, robust and portable.  The
       mount(8) command internally uses udev symlinks, so the use of symlinks in
       /etc/fstab has no advantage over tags.  For more details see libblkid(3).

       The proc filesystem is not associated with a special device, and when
       mounting it, an arbitrary keyword—for example, proc—can be used instead
       of a device specification.  (The customary choice none is less fortunate:
       the error message `none already mounted' from mount can be confusing.)

   The files /etc/fstab, /etc/mtab and /proc/mounts
       The file /etc/fstab (see fstab(5)), may contain lines describing what
       devices are usually mounted where, using which options.  The default
       location of the fstab(5) file can be overridden with the --fstab path
       command-line option (see below for more details).

       The command

              mount -a [-t type] [-O optlist]

       (usually given in a bootscript) causes all filesystems mentioned in fstab
       (of the proper type and/or having or not having the proper options) to be
       mounted as indicated, except for those whose line contains the noauto
       keyword.  Adding the -F option will make mount fork, so that the
       filesystems are mounted in parallel.

       When mounting a filesystem mentioned in fstab or mtab, it suffices to
       specify on the command line only the device, or only the mount point.

       The programs mount and umount traditionally maintained a list of
       currently mounted filesystems in the file /etc/mtab.  The support for
       regular classic /etc/mtab is completely disabled at compile time by
       default, because on current Linux systems it is better to make /etc/mtab
       a symlink to /proc/mounts instead. The regular mtab file maintained in
       userspace cannot reliably work with namespaces, containers and other
       advanced Linux features.  If the regular mtab support is enabled, then
       it's possible to use the file as well as the symlink.

       If no arguments are given to mount, the list of mounted filesystems is

       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

       Thus, given a line

              /dev/cdrom  /cd  iso9660  ro,user,noauto,unhide

       any user can mount the iso9660 filesystem found on an inserted CDROM
       using the command:

              mount /cd

       Note that mount is very strict about non-root users and all paths
       specified on command line are verified before fstab is parsed or a helper
       program is executed. It's strongly recommended to use a valid mountpoint
       to specify filesystem, otherwise mount may fail. For example it's a bad
       idea to use NFS or CIFS source on command line.

       Since util-linux 2.35, mount does not exit when user permissions are
       inadequate according to libmount's internal security rules.  Instead, it
       drops suid permissions and continues as regular non-root user. This
       behavior supports use-cases where root permissions are not necessary
       (e.g., fuse filesystems, user namespaces, etc).

       For more details, see fstab(5).  Only the user that mounted a filesystem
       can unmount it again.  If any user should be able to unmount it, then use
       users instead of user in the fstab line.  The owner option is similar to
       the user option, with the restriction that the user must be the owner of
       the special file.  This may be useful e.g. for /dev/fd if a login script
       makes the console user owner of this device.  The group option is
       similar, with the restriction that the user must be a member of the group
       of the special file.

   Bind mount operation
       Remount part of the file hierarchy somewhere else.  The call is:

              mount --bind olddir newdir

       or by using this fstab entry:

              /olddir /newdir none bind

       After this call the same contents are accessible in two places.

       It is important to understand that "bind" does not create any second-
       class or special node in the kernel VFS. The "bind" is just another
       operation to attach a filesystem. There is nowhere stored information
       that the filesystem has been attached by a "bind" operation. The olddir
       and newdir are independent and the olddir may be unmounted.

       One can also remount a single file (on a single file).  It's also
       possible to use a bind mount to create a mountpoint from a regular
       directory, for example:

              mount --bind foo foo

       The bind mount call attaches only (part of) a single filesystem, not
       possible submounts.  The entire file hierarchy including submounts can be
       attached a second place by using:

              mount --rbind olddir newdir

       Note that the filesystem mount options maintained by the kernel will
       remain the same as those on the original mount point.  The userspace
       mount options (e.g., _netdev) will not be copied by mount and it's
       necessary to explicitly specify the options on the mount command line.

       Since util-linux 2.27 mount(8) permits changing the mount options by
       passing the relevant options along with --bind.  For example:

              mount -o bind,ro foo foo

       This feature is not supported by the Linux kernel; it is implemented in
       userspace by an additional mount(2) remounting system call.  This
       solution is not atomic.

       The alternative (classic) way to create a read-only bind mount is to use
       the remount operation, for example:

              mount --bind olddir newdir
              mount -o remount,bind,ro olddir newdir

       Note that a read-only bind will create a read-only mountpoint (VFS
       entry), but the original filesystem superblock will still be writable,
       meaning that the olddir will be writable, but the newdir will be read-

       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

       Since util-linux 2.31, mount ignores the bind flag from /etc/fstab on a
       remount operation (if "-o remount" is specified on command line).  This
       is necessary to fully control mount options on remount by command line.
       In previous versions the bind flag has been always applied and it was
       impossible to re-define mount options without interaction with the bind
       semantic. This mount(8) behavior does not affect situations when
       "remount,bind" is specified in the /etc/fstab file.

   The move operation
       Move a mounted tree to another place (atomically).  The call is:

              mount --move olddir newdir

       This will cause the contents which previously appeared under olddir to
       now be accessible under newdir.  The physical location of the files is
       not changed.  Note that olddir has to be a mountpoint.

       Note also that moving a mount residing under a shared mount is invalid
       and unsupported.  Use findmnt -o TARGET,PROPAGATION to see the current
       propagation flags.

   Shared subtree operations
       Since Linux 2.6.15 it is possible to mark a mount and its submounts as
       shared, private, slave or unbindable.  A shared mount provides the
       ability to create mirrors of that mount such that mounts and unmounts
       within any of the mirrors propagate to the other mirror.  A slave mount
       receives propagation from its master, but not vice versa.  A private
       mount carries no propagation abilities.  An unbindable mount is a private
       mount which cannot be cloned through a bind operation.  The detailed
       semantics are documented in Documentation/filesystems/sharedsubtree.txt
       file in the kernel source tree; see also mount_namespaces(7).

       Supported operations are:

              mount --make-shared mountpoint
              mount --make-slave mountpoint
              mount --make-private mountpoint
              mount --make-unbindable mountpoint

       The following commands allow one to recursively change the type of all
       the mounts under a given mountpoint.

              mount --make-rshared mountpoint
              mount --make-rslave mountpoint
              mount --make-rprivate mountpoint
              mount --make-runbindable mountpoint

       mount(8) does not read fstab(5) when a --make-* operation is requested.
       All necessary information has to be specified on the command line.

       Note that the Linux kernel does not allow changing multiple propagation
       flags with a single mount(2) system call, and the flags cannot be mixed
       with other mount options and operations.

       Since util-linux 2.23 the mount command can be used to do more
       propagation (topology) changes by one mount(8) call and do it also
       together with other mount operations.  This feature is EXPERIMENTAL.  The
       propagation flags are applied by additional mount(2) system calls when
       the preceding mount operations were successful.  Note that this use case
       is not atomic.  It is possible to specify the propagation flags in
       fstab(5) as mount options (private, slave, shared, unbindable, rprivate,
       rslave, rshared, runbindable).

       For example:

              mount --make-private --make-unbindable /dev/sda1 /foo

       is the same as:

              mount /dev/sda1 /foo
              mount --make-private /foo
              mount --make-unbindable /foo

       The full set of mount options used by an invocation of mount is
       determined by first extracting the mount options for the filesystem from
       the fstab table, then applying any options specified by the -o argument,
       and finally applying a -r or -w option, when present.

       The mount command does not pass all command-line options to the
       /sbin/mount.suffix mount helpers.  The interface between mount and the
       mount helpers is described below in the section EXTERNAL HELPERS.

       Command-line options available for the mount command are:

       -a, --all
              Mount all filesystems (of the given types) mentioned in fstab
              (except for those whose line contains the noauto keyword).  The
              filesystems are mounted following their order in fstab.  The mount
              command compares filesystem source, target (and fs root for bind
              mount or btrfs) to detect already mounted filesystems. The kernel
              table with already mounted filesystems is cached during mount
              --all. This means that all duplicated fstab entries will be

              The option --all is possible to use for remount operation too. In
              this case all filters (-t and -O) are applied to the table of
              already mounted filesystems.

              Since version 2.35 is possible to use the command line option -o
              to alter mount options from fstab (see also --options-mode).

              Note that it is a bad practice to use mount -a for fstab checking.
              The recommended solution is findmnt --verify.

       -B, --bind
              Remount a subtree somewhere else (so that its contents are
              available in both places).  See above, under Bind mounts.

       -c, --no-canonicalize
              Don't canonicalize paths.  The mount command canonicalizes all
              paths (from the command line or fstab) by default.  This option
              can be used together with the -f flag for already canonicalized
              absolute paths.  The option is designed for mount helpers which
              call mount -i.  It is strongly recommended to not use this
              command-line option for normal mount operations.

              Note that mount(8) does not pass this option to the
              /sbin/mount.type helpers.

       -F, --fork
              (Used in conjunction with -a.)  Fork off a new incarnation of
              mount for each device.  This will do the mounts on different
              devices or different NFS servers in parallel.  This has the
              advantage that it is faster; also NFS timeouts proceed in
              parallel.  A disadvantage is that the order of the mount
              operations is undefined.  Thus, you cannot use this option if you
              want to mount both /usr and /usr/spool.

       -f, --fake
              Causes everything to be done except for the actual system call; if
              it's not obvious, this ``fakes'' mounting the filesystem.  This
              option is useful in conjunction with the -v flag to determine what
              the mount command is trying to do.  It can also be used to add
              entries for devices that were mounted earlier with the -n option.
              The -f option checks for an existing record in /etc/mtab and fails
              when the record already exists (with a regular non-fake mount,
              this check is done by the kernel).

       -i, --internal-only
              Don't call the /sbin/mount.filesystem helper even if it exists.

       -L, --label label
              Mount the partition that has the specified label.

       -l, --show-labels
              Add the labels in the mount output.  mount must have permission to
              read the disk device (e.g. be set-user-ID root) for this to work.
              One can set such a label for ext2, ext3 or ext4 using the
              e2label(8) utility, or for XFS using xfs_admin(8), or for reiserfs
              using reiserfstune(8).

       -M, --move
              Move a subtree to some other place.  See above, the subsection The
              move operation.

       -n, --no-mtab
              Mount without writing in /etc/mtab.  This is necessary for example
              when /etc is on a read-only filesystem.

       -N, --namespace ns
              Perform the mount operation in the mount namespace specified by
              ns.  ns is either PID of process running in that namespace or
              special file representing that namespace.

              mount(8) switches to the mount namespace when it reads /etc/fstab,
              writes /etc/mtab (or writes to /run/mount) and calls the mount(2)
              system call, otherwise it runs in the original mount namespace.
              This means that the target namespace does not have to contain any
              libraries or other requirements necessary to execute the mount(2)

              See mount_namespaces(7) for more information.

       -O, --test-opts opts
              Limit the set of filesystems to which the -a option applies.  In
              this regard it is like the -t option except that -O is useless
              without -a.  For example, the command:

                     mount -a -O no_netdev

              mounts all filesystems except those which have the option _netdev
              specified in the options field in the /etc/fstab file.

              It is different from -t in that each option is matched exactly; a
              leading no at the beginning of one option does not negate the

              The -t and -O options are cumulative in effect; that is, the

                     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

       -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

       --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

       -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)

       -s     Tolerate sloppy mount options rather than failing.  This will
              ignore mount options not supported by a filesystem type.  Not all
              filesystems support this option.  Currently it's supported by the
              mount.nfs mount helper only.

       --source device
              If only one argument for the mount command is given, then the
              argument might be interpreted as the target (mountpoint) or source
              (device).  This option allows you to explicitly define that the
              argument is the mount source.

       --target directory
              If only one argument for the mount command is given, then the
              argument might be interpreted as the target (mountpoint) or source
              (device).  This option allows you to explicitly define that the
              argument is the mount target.

       --target-prefix directory
              Prepend the specified directory to all mount targets.  This option
              can be used to follow fstab, but mount operations are done in
              another place, for example:

                     mount --all --target-prefix /chroot -o X-mount.mkdir

              mounts all from system fstab to /chroot, all missing mountpoint
              are created (due to X-mount.mkdir).  See also --fstab to use an
              alternative fstab.

       -T, --fstab path
              Specifies an alternative fstab file.  If path is a directory, then
              the files in the directory are sorted by strverscmp(3); files that
              start with "." or without an .fstab extension are ignored.  The
              option can be specified more than once.  This option is mostly
              designed for initramfs or chroot scripts where additional
              configuration is specified beyond standard system configuration.

              Note that mount(8) does not pass the option --fstab to the
              /sbin/mount.type helpers, meaning that the alternative fstab files
              will be invisible for the helpers.  This is no problem for normal
              mounts, but user (non-root) mounts always require fstab to verify
              the user's rights.

       -t, --types fstype
              The argument following the -t is used to indicate the filesystem
              type.  The filesystem types which are currently supported depend
              on the running kernel.  See /proc/filesystems and
              /lib/modules/$(uname -r)/kernel/fs for a complete list of the
              filesystems.  The most common are ext2, ext3, ext4, xfs, btrfs,
              vfat, sysfs, proc, nfs and cifs.

              The programs mount and umount support filesystem subtypes.  The
              subtype is defined by a '.subtype' suffix.  For example
              'fuse.sshfs'.  It's recommended to use subtype notation rather
              than add any prefix to the mount source (for example
              '' is deprecated).

              If no -t option is given, or if the auto type is specified, mount
              will try to guess the desired type.  Mount uses the blkid library
              for guessing the filesystem type; if that does not turn up
              anything that looks familiar, mount will try to read the file
              /etc/filesystems, or, if that does not exist, /proc/filesystems.
              All of the filesystem types listed there will be tried, except for
              those that are labeled "nodev" (e.g. devpts, proc and nfs).  If
              /etc/filesystems ends in a line with a single *, mount will read
              /proc/filesystems afterwards.  While trying, all filesystem types
              will be mounted with the mount option silent.

              The auto type may be useful for user-mounted floppies.  Creating a
              file /etc/filesystems can be useful to change the probe order
              (e.g., to try vfat before msdos or ext3 before ext2) or if you use
              a kernel module autoloader.

              More than one type may be specified in a comma-separated list, for
              the -t option as well as in an /etc/fstab entry.  The list of
              filesystem types for the -t option can be prefixed with no to
              specify the filesystem types on which no action should be taken.
              The prefix no has no effect when specified in an /etc/fstab entry.

              The prefix no can be meaningful with the -a option.  For example,
              the command

                     mount -a -t nomsdos,smbfs

              mounts all filesystems except those of type msdos and smbfs.

              For most types all the mount program has to do is issue a simple
              mount(2) system call, and no detailed knowledge of the filesystem
              type is required.  For a few types however (like nfs, nfs4, cifs,
              smbfs, ncpfs) an ad hoc code is necessary.  The nfs, nfs4, cifs,
              smbfs, and ncpfs filesystems have a separate mount program.  In
              order to make it possible to treat all types in a uniform way,
              mount will execute the program /sbin/mount.type (if that exists)
              when called with type type.  Since different versions of the
              smbmount program have different calling conventions,
              /sbin/mount.smbfs may have to be a shell script that sets up the
              desired call.

       -U, --uuid uuid
              Mount the partition that has the specified uuid.

       -v, --verbose
              Verbose mode.

       -w, --rw, --read-write
              Mount the filesystem read/write.  Read-write is the kernel default
              and the mount default is to try read-only if the previous mount
              syscall with read-write flags on write-protected devices of
              filesystems failed.

              A synonym is -o rw.

              Note that specifying -w on the command line forces mount to never
              try read-only mount on write-protected devices or already mounted
              read-only filesystems.

       -V, --version
              Display version information and exit.

       -h, --help
              Display help text and exit.

       Some of these options are only useful when they appear in the /etc/fstab

       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

       The following options apply to any filesystem that is being mounted (but
       not every filesystem actually honors them – e.g., the sync option today
       has an effect only for ext2, ext3, ext4, fat, vfat, ufs and xfs):

       async  All I/O to the filesystem should be done asynchronously.  (See
              also the sync option.)

       atime  Do not use the noatime feature, so the inode access time is
              controlled by kernel defaults.  See also the descriptions of the
              relatime and strictatime mount options.

              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

       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

              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

              Note that the real set of all default mount options depends on the
              kernel and filesystem type.  See the beginning of this section for
              more details.

       dev    Interpret character or block special devices on the filesystem.

       nodev  Do not interpret character or block special devices on the

              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 rename.

       exec   Permit execution of binaries.

       noexec Do not permit direct execution of any binaries on the mounted

       group  Allow an ordinary user to mount the filesystem if one of that
              user's groups matches the group of the device.  This option
              implies the options nosuid and nodev (unless overridden by
              subsequent options, as in the option line group,dev,suid).

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

              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

              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

              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.

              Use the kernel's default behavior for inode access time updates.

              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

              The on-disk timestamps are updated only when:

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

              - 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

              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

                  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

                  mount --all -o remount,ro -t vfat

              remounts all already mounted vfat filesystems in read-only mode.
              Each of the filesystems is remounted by "mount -o remount,ro /dir"
              semantic.  This means the mount command reads fstab or mtab and
              merges these options with the options from the command line.

       ro     Mount the filesystem read-only.

       rw     Mount the filesystem read-write.

       sync   All I/O to the filesystem should be done synchronously.  In the
              case of media with a limited number of write cycles (e.g. some
              flash drives), sync may cause life-cycle shortening.

       user   Allow an ordinary user to mount the filesystem.  The name of the
              mounting user is written to the mtab file (or to the private
              libmount file in /run/mount on systems without a regular mtab) so
              that this same user can unmount the filesystem again.  This option
              implies the options noexec, nosuid, and nodev (unless overridden
              by subsequent options, as in the option line user,exec,dev,suid).

       nouser Forbid an ordinary user to mount the filesystem.  This is the
              default; it does not imply any other options.

       users  Allow any user to mount and to unmount the filesystem, even when
              some other ordinary user mounted it.  This option implies the
              options noexec, nosuid, and nodev (unless overridden by subsequent
              options, as in the option line users,exec,dev,suid).

       X-*    All options prefixed with "X-" are interpreted as comments or as
              userspace application-specific options.  These options are not
              stored in user space (e.g., mtab file), nor sent to the mount.type
              helpers nor to the mount(2) system call.  The suggested format is

       x-*    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

              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

              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:

       ownmask=value and othmask=value
              Set the permission mask for ADFS 'owner' permissions and 'other'
              permissions, respectively (default: 0700 and 0077, respectively).
              See also /usr/src/linux/Documentation/filesystems/adfs.rst.

   Mount options for affs
       uid=value and gid=value
              Set the owner and group of the root of the filesystem (default:
              uid=gid=0, but with option uid or gid without specified value, the
              UID and GID of the current process are taken).

       setuid=value and setgid=value
              Set the owner and group of all files.

              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 filesystem.

       usemp  Set UID and GID of the root of the filesystem to the UID and GID
              of the mount point upon the first sync or umount, and then clear
              this option.  Strange...

              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 device.

              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

       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

       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

              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 /dev/pts/ptmx).

              For compatibility with older versions of the kernel, the default
              mode of the new ptmx node is 0000.  ptmxmode=value specifies a
              more useful mode for the ptmx node and is highly recommended when
              the newinstance option is specified.

              This option is only implemented in Linux kernel versions starting
              with 2.6.29.  Further, this option is valid only if
              CONFIG_DEVPTS_MULTIPLE_INSTANCES is enabled in the kernel

   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 octal.

              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 default.

                     Like "normal", but names that contain long parts or special
                     characters that are sometimes used on Linux but are not
                     accepted by MS-DOS (+, =, etc.) are rejected.

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

              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 obsolete.

              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 images.

              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 format.

              Enable this only if you want to export the FAT filesystem over

              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

              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

       quiet  Turn on the quiet flag.  Attempts to chown or chmod files do not
              return errors, although they fail.  Use with caution!

       rodir  FAT has the ATTR_RO (read-only) attribute.  On Windows, the
              ATTR_RO of the directory will just be ignored, and is used only by
              applications as a flag (e.g. it's set for the customized folder).

              If you want to use ATTR_RO as read-only flag even for the
              directory, set this option.

              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

              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:

              This option is obsolete and may fail or being ignored.

              Do not abort mounting when certain consistency checks fail.

   Mount options for iso9660
       ISO 9660 is a standard describing a filesystem structure to be used on
       CD-ROMs. (This filesystem type is also seen on some DVDs.  See also the
       udf filesystem.)

       Normal iso9660 filenames appear in an 8.3 format (i.e., DOS-like
       restrictions on filename length), and in addition all characters are in
       upper case.  Also there is no field for file ownership, protection,
       number of links, provision for block/character devices, etc.

       Rock Ridge is an extension to iso9660 that provides all of these UNIX-
       like features.  Basically there are extensions to each directory record
       that supply all of the additional information, and when Rock Ridge is in
       use, the filesystem is indistinguishable from a normal UNIX filesystem
       (except that it is read-only, of course).

       norock Disable the use of Rock Ridge extensions, even if available.  Cf.

              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: check=strict.)

       uid=value and gid=value
              Give all files in the filesystem the indicated user or group id,
              possibly overriding the information found in the Rock Ridge
              extensions.  (Default: uid=0,gid=0.)

              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.

              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: block=1024.)

              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 iso8859-1.

       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

              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 behavior.

              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 it.

   Mount options for ncpfs
       Just like nfs, the ncpfs implementation expects a binary argument (a
       struct ncp_mount_data) to the mount system call.  This argument is
       constructed by ncpmount(8) and the current version of mount (2.12) does
       not know anything about ncpfs.

   Mount options for ntfs
              Character set to use when returning file names.  Unlike VFAT, NTFS
              suppresses names that contain nonconvertible characters.

              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 obsolete.

       uid=value, gid=value and umask=value
              Set the file permission on the filesystem.  The umask value is
              given in octal.  By default, the files are owned by root and not
              readable by somebody else.

   Mount options for overlay
       Since Linux 3.18 the overlay pseudo filesystem implements a union mount
       for other filesystems.

       An overlay filesystem combines two filesystems - an upper filesystem and
       a lower filesystem.  When a name exists in both filesystems, the object
       in the upper filesystem is visible while the object in the lower
       filesystem is either hidden or, in the case of directories, merged with
       the upper object.

       The lower filesystem can be any filesystem supported by Linux and does
       not need to be writable.  The lower filesystem can even be another
       overlayfs.  The upper filesystem will normally be writable and if it is
       it must support the creation of trusted.* extended attributes, and must
       provide a valid d_type in readdir responses, so NFS is not suitable.

       A read-only overlay of two read-only filesystems may use any filesystem
       type.  The options lowerdir and upperdir are combined into a merged
       directory by using:

              mount -t overlay  overlay  \
                -olowerdir=/lower,upperdir=/upper,workdir=/work  /merged

              Any filesystem, does not need to be on a writable filesystem.

              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

                     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

       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 reiserfsck.

              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 page.

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

       barrier=none / barrier=flush
              This disables / enables the use of write barriers in the
              journaling code.  barrier=none disables, barrier=flush enables
              (default).  This also requires an IO stack which can support
              barriers, and if reiserfs gets an error on a barrier write, it
              will disable barriers again with a warning.  Write barriers
              enforce proper on-disk ordering of journal commits, making
              volatile disk write caches safe to use, at some performance
              penalty.  If your disks are battery-backed in one way or another,
              disabling barriers may safely improve performance.

   Mount options for ubifs
       UBIFS is a flash filesystem which works on top of UBI volumes.  Note that
       atime is not supported and is always turned off.

       The device name may be specified as

              ubiX_Y UBI device number X, volume number Y

              ubiY   UBI device number 0, volume number Y

                     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 "forget".

       gid=   Make all files in the filesystem belong to the given group.
              gid=forget can be specified independently of (or usually in
              addition to) gid=<group> and results in UDF not storing gids to
              the media. In fact the recorded gid is the 32-bit overflow gid -1
              as defined by the UDF standard.  The value is given as either
              <group> which is a valid group name or the corresponding decimal
              group id, or the special string "forget".

       umask= Mask out the given permissions from all inodes read from the
              filesystem.  The value is given in octal.

       mode=  If mode= is set the permissions of all non-directory inodes read
              from the filesystem will be set to the given mode. The value is
              given in octal.

       dmode= If dmode= is set the permissions of all directory inodes read from
              the filesystem will be set to the given dmode. The value is given
              in octal.

       bs=    Set the block size. Default value prior to kernel version 2.6.30
              was 2048. Since 2.6.30 and prior to 4.11 it was logical device
              block size with fallback to 2048. Since 4.11 it is logical block
              size with fallback to any valid block size between logical device
              block size and 4096.

              For other details see the mkudffs(8) 2.0+ manpage, sections

       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

              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 removed
              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 Sparc.

              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-only.

                     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

   Mount options for vfat
       First of all, the mount options for fat are recognized.  The dotsOK
       option is explicitly killed by vfat.  Furthermore, there are

              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 disabled.

              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

              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

       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 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 verity.roothash.

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

              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.

       mount has the following exit status values (the bits can be ORed):

       0      success

       1      incorrect invocation or permissions

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

       4      internal mount bug

       8      user interrupt

       16     problems writing or locking /etc/mtab

       32     mount failure

       64     some mount succeeded

              The command mount -a returns 0 (all succeeded), 32 (all failed),
              or 64 (some failed, some succeeded).

       The syntax of external mount helpers is:

           /sbin/mount.suffix spec dir [-sfnv] [-N namespace] [-o options] [-t

       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

       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.

              overrides the default location of the fstab file (ignored for

              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

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

       /etc/fstab        filesystem table

       /run/mount        libmount private runtime directory

       /etc/mtab         table of mounted filesystems or symlink to /proc/mounts

       /etc/mtab~        lock file (unused on systems with mtab symlink)

       /etc/mtab.tmp     temporary file (unused on systems with mtab symlink)

       /etc/filesystems  a list of filesystem types to try

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

       It is possible for a corrupted filesystem to cause a crash.

       Some Linux filesystems don't support -o sync and -o dirsync (the ext2,
       ext3, ext4, fat and vfat filesystems do support synchronous updates (a la
       BSD) when mounted with the sync option).

       The -o remount may not be able to change mount parameters (all ext2fs-
       specific parameters, except sb, are changeable with a remount, for
       example, but you can't change gid or umask for the fatfs).

       It is possible that the files /etc/mtab and /proc/mounts don't match on
       systems with a regular mtab file.  The first file is based only on the
       mount command options, but the content of the second file also depends on
       the kernel and others settings (e.g. on a remote NFS server -- in certain
       cases the mount command may report unreliable information about an NFS
       mount point and the /proc/mount file usually contains more reliable
       information.)  This is another reason to replace the mtab file with a
       symlink to the /proc/mounts file.

       Checking files on NFS filesystems referenced by file descriptors (i.e.
       the fcntl and ioctl families of functions) may lead to inconsistent
       results due to the lack of a consistency check in the kernel even if the
       noac mount option is used.

       The loop option with the offset or sizelimit options used may fail when
       using older kernels if the mount command can't confirm that the size of
       the block device has been configured as requested.  This situation can be
       worked around by using the losetup command manually before calling mount
       with the configured loop device.

       Karel Zak <>

       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),

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

util-linux                         August 2015                          MOUNT(8)