MOUNT(8)                    System Administration                   MOUNT(8)

NAME         top

       mount - mount a filesystem

SYNOPSIS         top

       mount [-l|-h|-V]

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

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

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

DESCRIPTION         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 another services.

       The standard form of the mount command is:

              mount -t type device dir

       This tells the kernel to attach the filesystem found on device (which
       is of type type) at the directory dir.  The option -t type is
       optional.  The mount command is usually able to detect a filesystem.
       The root permissions are necessary to mount a filesystem by default.
       See 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 ambivalent interpretation of the given
       argument.  For example:

              mount --target /mountpoint

   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  It
       is also possible to indicate a block special device using its
       filesystem label or UUID (see the -L and -U options below), or its
       partition label or UUID.  Partition identifiers are supported for
       example for GUID Partition Tables (GPT).

       The device name of disk partitions are unstable; hardware
       reconfiguration, adding or removing a device can cause change in
       names. This is reason why it's strongly recommended to use filesystem
       or partition identificators like UUID or LABEL.

       The command lsblk --fs provides 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,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).

       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.

       The proc filesystem is not associated with a special device, and when
       mounting it, an arbitrary keyword, such as proc can be used instead
       of a device specification.  (The customary choice none is less
       fortunate: the error message `none busy' from umount can be

   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 simultaneously.

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

       The programs mount and umount traditionally maintained a list of
       currently mounted filesystems in the file /etc/mtab.  This real mtab
       file is still supported, but on current Linux systems it is better to
       make it a symlink to /proc/mounts instead, because a regular mtab
       file maintained in userspace cannot reliably work with namespaces,
       containers and other advanced Linux features.

       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.  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, PARTUUID or PARTLABEL) and dir are specified.  For
       example, to mount device foo at /dir:

              mount /dev/foo /dir

   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 bad idea to use NFS or CIFS source on command line.

       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 member of the group of the special file.

   Bind mounts
       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.  One
       can also remount a single file (on a single file).  It's also
       possible to use the 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 is
       attached a second place by using:

              mount --rbind olddir newdir

       Note that the filesystem mount options will remain the same as those
       on the original mount point.

       mount(8) since v2.27 allows to change the mount options by passing
       the relevant options along with --bind.  For example:

              mount -o bind,ro foo foo

       This feature is not supported by the Linux kernel; it is implemented
       in userspace by an additional mount(2) remounting system call.  This
       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 by "remount,bind" operation.
       It's impossible to change mount options recursively (for example with
       -o rbind,ro).

       mount(8) since v2.31 ignores the bind flag from /etc/fstab on remount
       operation (if "-o remount" specified on command line). This is
       necessary to fully control mount options on remount by command line.
       In the 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

       Supported operations are:

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

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

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

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

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

       Since util-linux 2.23 the mount command allows to use several
       propagation flags together and 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 command mount does not pass all command-line options to the
       /sbin/mount.suffix mount helpers.  The interface between mount and
       the mount helpers is described below in the section EXTERNAL HELPERS.

       Command-line options available for the mount command are:

       -a, --all
              Mount all filesystems (of the given types) mentioned in fstab
              (except for those whose line contains the noauto keyword).
              The filesystems are mounted following their order in fstab.

              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 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

              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 go in parallel.
              A disadvantage is that the mounts are done in undefined order.
              Thus, you cannot use this option if you want to mount both
              /usr and /usr/spool.

       -f, --fake
              Causes everything to be done except for the actual system
              call; if it's not obvious, this ``fakes'' mounting the
              filesystem.  This option is useful in conjunction with the -v
              flag to 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 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.

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

                     mount -a -O no_netdev

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

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

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

                     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 FILESYSTEM-SPECIFIC MOUNT OPTIONS sections.

       -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 target (mountpoint) or source
              (device).  This option allows 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 target (mountpoint) or source
              (device).  This option allows to explicitly define that the
              argument is the mount target.

       -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 option -t as well as in an /etc/fstab entry.  The list of
              filesystem types for option -t 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. The read-write is kernel
              default.  A synonym is -o rw.

              Note that specify -w on command line forces mount command to
              never try read-only mount on write-protected devices. The
              default is try read-only if the previous mount syscall with
              read-write flags failed.

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

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


       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, fat, vfat and ufs):

       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 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 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

              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
              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
              file system.

              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

       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 /proc/mounts.

              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 i-node was written
              to disk.

              Do not use the lazytime feature.

       suid   Allow set-user-ID or set-group-ID bits to take effect.

       nosuid Do not allow set-user-ID or set-group-ID bits to take effect.

       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
              semantic. See above, the subsection Bind mounts.

              The  remount  functionality follows the standard way the mount
              command works with options from fstab.  This means that  mount
              does  not  read  fstab (or mtab) only when both device and dir
              are specified.

                  mount -o remount,rw /dev/foo /dir

              After this  call  all  old  mount  options  are  replaced  and
              arbitrary  stuff  from  fstab (or mtab) is ignored, except the
              loop= option which is internally generated and  maintained  by
              the mount 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

       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

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

       x-*    The  same  as  X-* options, but stored permanently in the user
              space. It means the options are also available for  umount  or
              another  operations.  Note that maintain mount options in user
              space is tricky, because it's  necessary  use  libmount  based
              tools  and  there  is  no  guarantee  that the options will be
              always 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  have  X-* now), but due to
              growing number of use-cases  (in  initrd,  systemd  etc.)  the
              functionality  have  been  extended  to  keep  existing  fstab
              configurations usable without a change.

              Allow to make a target directory (mountpoint).   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.  The option is
              also supported as x-mount.mkdir, this notation  is  deprecated
              for mount.mkdir since v2.30.


       The following options apply only to certain filesystems.  We sort
       them by filesystem.  They all follow the -o flag.

       What options are supported depends a bit on the running kernel.  More
       info may be found in the kernel source subdirectory

   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

       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 btrfs
       Btrfs is a copy-on-write filesystem for Linux aimed at implementing
       advanced features while focusing on fault tolerance, repair, and easy

              Debugging option to force all block allocations above a
              certain byte threshold on each block device.  The value is
              specified in bytes, optionally with a K, M, or G suffix, case
              insensitive.  Default is 1MB.

              Disable/enable auto defragmentation.  Auto defragmentation
              detects small random writes into files and queues them up for
              the defrag process.  Works best for small files; not well-
              suited for large database workloads.

              These debugging options control the behavior of the integrity
              checking module(the BTRFS_FS_CHECK_INTEGRITY config option

              check_int enables the integrity checker module, which examines
              all block-write requests to ensure on-disk consistency, at a
              large memory and CPU cost.

              check_int_data includes extent data in the integrity checks,
              and implies the check_int option.

              check_int_print_mask takes a bitmask of BTRFSIC_PRINT_MASK_*
              values as defined in fs/btrfs/check-integrity.c, to control
              the integrity checker module behavior.

              See comments at the top of fs/btrfs/check-integrity.c for more

              Set the interval of periodic commit, 30 seconds by default.
              Higher values defer data being synced to permanent storage,
              with obvious consequences when the system crashes.  The upper
              bound is not forced, but a warning is printed if it's more
              than 300 seconds (5 minutes).

              Control BTRFS file data compression.  Type may be specified as
              "zlib" "lzo" or "no" (for no compression, used for
              remounting).  If no type is specified, zlib is used.  If
              compress-force is specified, all files will be compressed,
              whether or not they compress well.  If compression is enabled,
              nodatacow and nodatasum are disabled.

              Allow mounts to continue with missing devices.  A read-write
              mount may fail with too many devices missing, for example if a
              stripe member is completely missing.

              Specify a device during mount so that ioctls on the control
              device can be avoided.  Especially useful when trying to mount
              a multi-device setup as root.  May be specified multiple times
              for multiple devices.

              Disable/enable the discard mount option.  The discard function
              issues frequent commands to let the block device reclaim space
              freed by the filesystem.  This is useful for SSD devices,
              thinly provisioned LUNs and virtual machine images, but may
              have a significant performance impact.  (The fstrim command is
              also available to initiate batch trims from userspace.)

              Disable/enable debugging option to be more verbose in some
              ENOSPC conditions.

              Action to take when encountering a fatal error:
                "bug" - BUG() on a fatal error.  This is the default.
                "panic" - panic() on a fatal error.

              The flushoncommit mount option forces any data dirtied by a
              write in a prior transaction to commit as part of the current
              commit.  This makes the committed state a fully consistent
              view of the filesystem from the application's perspective
              (i.e., it includes all completed filesystem operations).  This
              was previously the behavior only when a snapshot is created.

              Enable free inode number caching.   Defaults to off due to an
              overflow problem when the free space CRCs don't fit inside a
              single page.

              Specify the maximum amount of space, in bytes, that can be
              inlined in a metadata B-tree leaf.  The value is specified in
              bytes, optionally with a K, M, or G suffix, case insensitive.
              In practice, this value is limited by the root sector size,
              with some space unavailable due to leaf headers.  For a 4k
              sectorsize, max inline data is ~3900 bytes.

              Specify that 1 metadata chunk should be allocated after every
              value data chunks.  Off by default.

       noacl  Enable/disable support for Posix Access Control Lists (ACLs).
              See the acl(5) manual page for more information about ACLs.

              Enable/disable the use of block-layer write barriers.  Write
              barriers ensure that certain IOs make it through the device
              cache and are on persistent storage.  If disabled on a device
              with a volatile (non-battery-backed) write-back cache, the
              nobarrier option will lead to filesystem corruption on a
              system crash or power loss.

              Enable/disable data copy-on-write for newly created files.
              This option implies nodatasum, and disables all compression.

              Enable/disable data checksumming for newly created files.
              This option implies datacow.

              Enable/disable the tree logging used for fsync and O_SYNC

              Enable autorecovery attempts if a bad tree root is found at
              mount time.  Currently this scans a list of several previous
              tree roots and tries to use the first readable.

              Force check and rebuild procedure of the UUID tree.  This
              should not normally be needed.

              Skip automatic resume of an interrupted balance operation
              after mount.  May be resumed with "btrfs balance resume."

              Disable freespace cache loading without clearing the cache.

              Force clearing and rebuilding of the disk space cache if
              something has gone wrong.

              Options to control ssd allocation schemes.  By default, BTRFS
              will enable or disable ssd allocation heuristics depending on
              whether a rotational or non-rotational disk is in use.  The
              ssd and nossd options can override this autodetection.

              The ssd_spread mount option attempts to allocate into big
              chunks of unused space, and may perform better on low-end
              ssds.  ssd_spread implies ssd, enabling all other ssd
              heuristics as well.

              Mount subvolume at path rather than the root subvolume.  The
              path is relative to the top level subvolume.

              Mount subvolume specified by an ID number rather than the root
              subvolume.  This allows mounting of subvolumes which are not
              in the root of the mounted filesystem.  You can use "btrfs
              subvolume list" to see subvolume ID numbers.

       subvolrootid=objectid  (deprecated)
              Mount subvolume specified by objectid rather than the root
              subvolume.  This allows mounting of subvolumes which are not
              in the root of the mounted filesystem.  You can use "btrfs
              subvolume show " to see the object ID for a subvolume.

              The number of worker threads to allocate.  The default number
              is equal to the number of CPUs + 2, or 8, whichever is

              Allow subvolumes to be deleted by a non-root user.  Use with

   Mount options for cifs
       See the options section of the mount.cifs(8) man page (cifs-utils
       package must be installed).

   Mount options for coherent

   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

       uid=value and gid=value
              This sets the owner or the group of newly created PTYs to the
              specified values.  When nothing is specified, they will be set
              to the UID and GID of the creating process.  For example, if
              there is a tty group with GID 5, then gid=5 will cause newly
              created PTYs to belong to the tty group.

              Set the mode of newly created PTYs to the specified value.
              The default is 0600.  A value of mode=620 and gid=5 makes
              "mesg y" the default on newly created PTYs.

              Create a private instance of devpts filesystem, such that
              indices of ptys allocated in this new instance are independent
              of indices created in other instances of devpts.

              All mounts of devpts without this newinstance option share the
              same set of pty indices (i.e legacy mode).  Each mount of
              devpts with the newinstance option has a private set of pty

              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

              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 ext2, ext3 and ext4
       See the options section of the ext2(5), ext3(5) or ext4(5) man page
       (the e2fsprogs package must be installed).

   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

              This option controls the permission check of mtime/atime.

              20     If current process is in group of file's group ID, you
                     can change timestamp.

              2      Other users can change timestamp.

              The default is set from `dmask' option. (If the directory is
              writable, utime(2) is also allowed.  I.e. ~dmask & 022)

              Normally utime(2) checks current process is owner of the file,
              or it has CAP_FOWNER capability.  But FAT filesystem doesn't
              have UID/GID on disk, so normal check is too inflexible.  With
              this option you can relax it.

              Three different levels of pickyness 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 being 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 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 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 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

       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 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 a 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,

       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 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:

              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

              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 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 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 minix

   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 nfs and nfs4
       See the options section of the nfs(5) man page (the nfs-utils package
       must be installed).

       The nfs and nfs4 implementation expects a binary argument (a struct
       nfs_mount_data) to the mount system call.  This argument is
       constructed by mount.nfs(8) and the current version of mount (2.13)
       does not know anything about nfs and nfs4.

   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

       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 proc
       uid=value and gid=value
              These options are recognized, but have no effect as far as I
              can see.

   Mount options for ramfs
       Ramfs is a memory based filesystem.  Mount it and you have it.
       Unmount it and it is gone.  There are no mount options.

   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

              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

              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

              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

              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(5) manual page.

       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 romfs

   Mount options for squashfs

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

   Mount options for sysv

   Mount options for tmpfs
              Override default maximum size of the filesystem.  The size is
              given in bytes, and rounded up to entire pages.  The default
              is half of the memory.  The size parameter also accepts a
              suffix % to limit this tmpfs instance to that percentage of
              your physical RAM: the default, when neither size nor
              nr_blocks is specified, is size=50%

              The same as size, but in blocks of PAGE_CACHE_SIZE

              The maximum number of inodes for this instance.  The default
              is half of the number of your physical RAM pages, or (on a
              machine with highmem) the number of lowmem RAM pages,
              whichever is the lower.

       The tmpfs mount options for sizing (size, nr_blocks, and nr_inodes)
       accept a suffix k, m or g for Ki, Mi, Gi (binary kilo (kibi), binary
       mega (mebi) and binary giga (gibi)) and can be changed on remount.

       mode=  Set initial permissions of the root directory.

       uid=   The user id.

       gid=   The group id.

              Set the NUMA memory allocation policy for all files in that
              instance (if the kernel CONFIG_NUMA is enabled) – which can be
              adjusted on the fly via 'mount -o remount ...'

                     prefers to allocate memory from the local node

                     prefers to allocate memory from the given Node

                     allocates memory only from nodes in NodeList

                     prefers to allocate from each node in turn

                     allocates from each node of NodeList in turn.

              The NodeList format is a comma-separated list of decimal
              numbers and ranges, a range being two "hyphen-minus"-separated
              decimal numbers, the smallest and largest node numbers in the
              range.  For example, mpol=bind:0–3,5,7,9–15

              Note that trying to mount a tmpfs with an mpol option will
              fail if the running kernel does not support NUMA; and will
              fail if its nodelist specifies a node which is not online.  If
              your system relies on that tmpfs being mounted, but from time
              to time runs a kernel built without NUMA capability (perhaps a
              safe recovery kernel), or with fewer nodes online, then it is
              advisable to omit the mpol option from automatic mount
              options.  It can be added later, when the tmpfs is already
              mounted on MountPoint, by 'mount -o
              remount,mpol=Policy:NodeList MountPoint'.

   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 file system.  Bulk-Read is an internal optimization.
              Some flashes may read faster if the data are read at one go,
              rather than at several read requests.  For example, OneNAND
              can do "read-while-load" if it reads more than one NAND page.

              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 the Optical
       Storage Technology Association, and is often used for DVD-ROM.  See
       also iso9660.

       gid=   Set the default group.

       umask= Set the default umask.  The value is given in octal.

       uid=   Set the default user.

       unhide Show otherwise hidden files.

              Show deleted files in lists.

              Unset strict conformance.

              Set the NLS character set.

       bs=    Set the block size. (May not work unless 2048.)

       novrs  Skip volume sequence recognition.

              Set the CDROM session counting from 0.  Default: last session.

              Override standard anchor location.  Default: 256.

              Override the VolumeDesc location. (unused)

              Override the PartitionDesc location. (unused)

              Set the last block of the filesystem.

              Override the fileset block location. (unused)

              Override the root directory location. (unused)

   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

              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

   Mount options for umsdos
       See mount options for msdos.  The dotsOK option is explicitly killed
       by umsdos.

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

              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),

       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 modes:

              lower  Force the short name to lower case upon display; store
                     a long name when the short name is not all upper case.

              win95  Force the short name to upper case upon display; store
                     a long name when the short name is not all upper case.

              winnt  Display the short name as is; store a long name when
                     the short name is not all lower case or all upper case.

              mixed  Display the short name as is; store a long name when
                     the short name is not all upper case.  This mode is the
                     default since Linux 2.6.32.

   Mount options for usbfs
       devuid=uid and devgid=gid and devmode=mode
              Set the owner and group and mode of the device files in the
              usbfs filesystem (default: uid=gid=0, mode=0644).  The mode is
              given in octal.

       busuid=uid and busgid=gid and busmode=mode
              Set the owner and group and mode of the bus directories in the
              usbfs filesystem (default: uid=gid=0, mode=0555).  The mode is
              given in octal.

       listuid=uid and listgid=gid and listmode=mode
              Set the owner and group and mode of the file devices (default:
              uid=gid=0, mode=0444).  The mode is given in octal.

   Mount options for xenix

   Mount options for xfs
       See the options section of the xfs(5) man page (the xfsprogs package
       must be installed).

THE LOOP DEVICE         top

       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 ext3 /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

       Since util-linux v2.29 mount command re-uses the loop device rather
       than initialize a new device if the same backing file is already used
       for some loop device with the same offset and sizelimit. This is
       necessary to avoid a filesystem corruption.

RETURN CODES         top

       mount has the following return codes (the bits can be ORed):

       0      success

       1      incorrect invocation or permissions

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

       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] [-o options] [-t

       where the suffix is the filesystem type and the -sfnvo 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 argument to the -o option.

FILES         top

       /etc/fstab        filesystem table

       /etc/mtab         table of mounted filesystems

       /etc/mtab~        lock file

       /etc/mtab.tmp     temporary file

       /etc/filesystems  a list of filesystem types to try

ENVIRONMENT         top

              overrides the default location of the fstab file (ignored for

              overrides the default location of the mtab file (ignored for

              enables libmount debug output

              enables libblkid debug output

              enables loop device setup debug output

SEE ALSO         top

       mount(2), umount(2), umount(8), fstab(5), nfs(5), xfs(5), e2label(8),
       findmnt(8), losetup(8), mke2fs(8), mountd(8), nfsd(8), swapon(8),
       tune2fs(8), xfs_admin(8)

BUGS         top

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

       Some Linux filesystems don't support -o sync nor -o dirsync (the
       ext2, ext3, 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/mounts 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 noac is used.

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

HISTORY         top

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

AUTHORS         top

       Karel Zak <>

AVAILABILITY         top

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

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
       2017-11-25.  (At that time, the date of the most recent commit that
       was found in the repository was 2017-11-23.)  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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