MOUNT(8)                     System Administration                    MOUNT(8)

       mount - mount a filesystem

       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

       All files accessible in a Unix system are arranged in one big tree, the
       file hierarchy, rooted at /.  These files can be spread out  over  sev-
       eral  devices.  The mount command serves to attach the filesystem found
       on some device to the big file tree.  Conversely, the umount(8) command
       will  detach  it  again.  The filesystem is used to control how data is
       stored on the device or provided in a virtual way by network or another

       The standard form of the mount command is:

              mount -t type device dir

       This  tells  the kernel to attach the filesystem found on device (which
       is of type type) at the directory dir.  The option -t type is optional.
       The  mount  command  is  usually able to detect a filesystem.  The root
       permissions are necessary to mount a filesystem by default.   See  sec-
       tion  "Non-superuser mounts" below for more details.  The previous con-
       tents (if any) and owner and mode of dir become invisible, and as  long
       as this filesystem remains mounted, the pathname dir refers to the root
       of the filesystem on device.

       If only the directory or the device is given, for example:

              mount /dir

       then mount looks for a mountpoint (and if not found then for a  device)
       in  the /etc/fstab file.  It's possible to use the --target or --source
       options to avoid ambivalent interpretation of the given argument.   For

              mount --target /mountpoint

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

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

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

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

              mount [-l] [-t type]

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

   Indicating the device and filesystem
       Most  devices  are indicated by a filename (of a block special device),
       like /dev/sda1, but there are other possibilities.  For example, in the
       case  of  an  NFS mount, device may look like  It is
       also possible to indicate a block special device using  its  filesystem
       label or UUID (see the -L and -U options below), or its partition label
       or UUID.  Partition identifiers are supported for example for GUID Par-
       tition Tables (GPT).

       The device names of disk partitions are unstable; hardware reconfigura-
       tion, adding or removing a device can cause changes in names.  This  is
       the reason why it's strongly recommended to use filesystem or partition
       identifiers like UUID or LABEL.

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

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

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

       Note that mount(8) uses UUIDs as strings.  The UUIDs from  the  command
       line  or from fstab(5) are not converted to internal binary representa-
       tion.  The string representation of the UUID should be based  on  lower
       case characters.

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

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

       The command

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

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

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

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

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

       If you want to override mount options from /etc/fstab you have  to  use
       the -o option:

              mount device|dir -o options

       and  then  the  mount options from the command line will be appended to
       the list of options from /etc/fstab.  This default behaviour is  possi-
       ble  to change by command line option --options-mode.  The usual behav-
       ior is that the last option wins if there are conflicting ones.

       The mount program does not read the /etc/fstab file if both device  (or
       LABEL,  UUID,  PARTUUID or PARTLABEL) and dir are specified.  For exam-
       ple, to mount device foo at /dir:

              mount /dev/foo /dir

       This default behaviour is possible to change  by  command  line  option
       --options-source-force  to  always  read  configuration from fstab. For
       non-root users mount always read fstab configuration.

   Non-superuser mounts
       Normally, only the superuser  can  mount  filesystems.   However,  when
       fstab  contains the user option on a line, anybody can mount the corre-
       sponding filesystem.

       Thus, given a line

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

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

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

       Since  version  2.35  mount command does not exit when user permissions
       are inadequate by internal libmount security rules.  It drops suid per-
       missions  and  continue  as regular non-root user. It allows to support
       use-cases where root permissions are not necessary (e.g., fuse filesys-
       tems, user namespaces, etc).

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

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

              mount --bind olddir newdir

       or by using this fstab entry:

              /olddir /newdir none bind

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

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

       One can also remount a single file (on a single file).  It's also  pos-
       sible  to  use the bind mount to create a mountpoint from a regular di-
       rectory, for example:

              mount --bind foo foo

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

              mount --rbind olddir newdir

       Note that the filesystem mount options maintained by kernel will remain
       the same as those on the original mount point.  The userspace mount op-
       tions (e.g., _netdev) will not be copied by mount(8) and it's necessary
       explicitly specify the options on mount command line.

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

              mount -o bind,ro foo foo

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

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

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

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

       It's also possible to change nosuid, nodev, noexec, noatime, nodiratime
       and  relatime VFS entry flags by "remount,bind" operation.  The another
       (for example filesystem specific flags) are silently ignored.  It's im-
       possible  to  change  mount  options  recursively  (for example with -o

       mount(8) since v2.31 ignores the bind flag from /etc/fstab  on  remount
       operation  (if  "-o remount" specified on command line). This is neces-
       sary to fully control mount options on remount by command line. In  the
       previous  versions the bind flag has been always applied and it was im-
       possible to re-define mount options without interaction with  the  bind
       semantic.  This  mount(8) behavior does not affect situations when "re-
       mount,bind" is specified in the /etc/fstab file.

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

              mount --move olddir newdir

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

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

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

       Supported operations are:

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

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

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

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

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

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

       For example:

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

       is the same as:

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

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

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

       Command-line options available for the mount command are:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              See namespaces(7) for more information.

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

                     mount -a -O no_netdev

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

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

              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.

       --options-mode mode
              Controls how to combine options  from  fstab/mtab  with  options
              from  command  line.  mode can be one of ignore, append, prepend
              or replace.  For example append means that  options  from  fstab
              are  appended  to  options  from command line.  Default value is
              prepend -- it means command line  options  are  evaluated  after
              fstab options.  Note that the last option wins if there are con-
              flicting ones.

       --options-source source
              Source of default options.  source is comma  separated  list  of
              fstab,  mtab  and  disable.  disable disables fstab and mtab and
              disables --options-source-force.  Default value is fstab,mtab.

              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  exam-
              ple,  ext3 and ext4 will replay the journal if the filesystem is
              dirty.  To prevent this kind of write access, you  may  want  to
              mount  an  ext3  or ext4 filesystem with the ro,noload mount op-
              tions or set the block device itself to read-only mode, see  the
              blockdev(8) command.

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

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

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

       --target-prefix directory
              Prepend specified directory to all mount targets.   This  option
              allows  to follow fstab, but mount operations is done on another
              place, for example:

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

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

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

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

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

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

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

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

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

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

                     mount -a -t nomsdos,smbfs

              mounts all filesystems except those of type msdos and smbfs.

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

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

       -v, --verbose
              Verbose mode.

       -w, --rw, --read-write
              Mount  the  filesystem  read/write. The read-write is kernel de-
              fault.  A synonym is -o rw.

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

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

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

       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

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

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

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

              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 ear-
              lier 2.4.<x> kernel versions.  Even where xattrs are  supported,
              you  can  save  time not having to label every file by assigning
              the entire disk one security context.

              A   commonly   used    option    for    removable    media    is

              Two  other options are fscontext= and defcontext=, both of which
              are mutually exclusive of the context option.   This  means  you
              can  use  fscontext  and defcontext with each other, but neither
              can be used with context.

              The fscontext= option works for all filesystems,  regardless  of
              their  xattr support.  The fscontext option sets the overarching
              filesystem label to a specific security context.  This  filesys-
              tem  label  is separate from the individual labels on the files.
              It represents the entire filesystem for certain kinds of permis-
              sion  checks, such as during mount or file creation.  Individual
              file labels are still obtained from  the  xattrs  on  the  files
              themselves.  The context option actually sets the aggregate con-
              text that fscontext provides, in addition to supplying the  same
              label for individual files.

              You can set the default security context for unlabeled files us-
              ing defcontext= option.  This overrides the value set for  unla-
              beled  files  in  the policy and requires a filesystem that sup-
              ports xattr labeling.

              The rootcontext= option allows you to explicitly label the  root
              inode of a FS being mounted before that FS or inode becomes vis-
              ible to userspace.  This was found to be useful for things  like
              stateless linux.

              Note  that  the kernel rejects any remount request that includes
              the context option, even when unchanged from  the  current  con-

              Warning:  the  context value might contain commas, in which case
              the value has to be properly quoted, otherwise mount(8) will in-
              terpret  the  comma as a separator between mount options.  Don't
              forget that the shell strips off quotes and thus double  quoting
              is required.  For example:

                     mount -t tmpfs none /mnt -o \

              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
              kernel  and  filesystem type.  See the beginning of this section
              for more details.

       dev    Interpret character or block special devices on the filesystem.

       nodev  Do not interpret character or block special devices on the  file

              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 syn-
              chronously.  This affects the  following  system  calls:  creat,
              link, unlink, symlink, mkdir, rmdir, mknod and rename.

       exec   Permit execution of binaries.

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

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

              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 ear-
              lier than the  current  modify  or  change  time.   (Similar  to
              noatime,  but  it  doesn't break mutt or other applications that
              need to know if a file has been read since the last time it  was

              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  ta-
              ble  for workloads that perform frequent random writes to preal-
              located files.

              The on-disk timestamps are updated only when:

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

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

              - an undeleted inode is evicted from memory

              - more than 24 hours have passed since the i-node was written to

              Do not use the lazytime feature.

       suid   Honor set-user-ID and set-group-ID  bits  or  file  capabilities
              when executing programs from this filesystem.

       nosuid Do not honor set-user-ID and set-group-ID bits or file capabili-
              ties when executing programs from this filesystem.

       silent Turn on the silent flag.

       loud   Turn off the silent flag.

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

              Attempt  to remount an already-mounted filesystem.  This is com-
              monly used to change the mount flags  for  a  filesystem,  espe-
              cially  to  make  a  readonly  filesystem writable.  It does not
              change device or mount point.

              The remount operation together with the bind  flag  has  special
              semantic. See above, the subsection Bind mounts.

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

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

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

                  mount -o remount,rw  /dir

              After this call, mount reads fstab and merges these options with
              the options from the command line (-o).   If  no  mountpoint  is
              found  in  fstab,  then a remount with unspecified source is al-

              mount(8) allows to use --all  to  remount  all  already  mounted
              filesystems which match a specified filter (-O and -t).  For ex-

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

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

       ro     Mount the filesystem read-only.

       rw     Mount the filesystem read-write.

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

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

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

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

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

       x-*    The  same  as  X-*  options,  but stored permanently in the user
              space. It means the options are also available for umount or an-
              other  operations.   Note  that  maintain  mount options in user
              space is tricky, because it's necessary use libmount based tools
              and there is no guarantee that the options will be always avail-
              able (for example after a move mount operation  or  in  unshared

              Note  that before util-linux v2.30 the x-* options have not been
              maintained by libmount and stored in user  space  (functionality
              was the same as have X-* now), but due to growing number of use-
              cases (in initrd, systemd etc.) the functionality have been  ex-
              tended  to  keep  existing fstab configurations usable without a

              Allow to make a target directory (mountpoint)  if  it  does  not
              exit  yet.   The optional argument mode specifies the filesystem
              access mode used for mkdir(2) in octal  notation.   The  default
              mode  is  0755.   This  functionality is supported only for root
              users or when mount executed without suid permissions.  The  op-
              tion is also supported as x-mount.mkdir, this notation is depre-
              cated since v2.30.

       You should consult the respective man page for  the  filesystem  first.
       If  you  want  to  know what options the ext4 filesystem supports, then
       check the ext4(5) man page.  If that doesn't exist, you can also  check
       the  corresponding  mount page like mount.cifs(8).  Note that you might
       have to install the respective userland tools.

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

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

   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,  respec-
              tively).    See    also    /usr/src/linux/Documentation/filesys-

   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 orig-
              inal 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 filesys-

       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 de-

              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  utili-
              ties may react to such strings in /etc/fstab.)

   Mount options for debugfs
       The debugfs filesystem is a pseudo filesystem, traditionally mounted on
       /sys/kernel/debug.  As of kernel version 3.4, debugfs has the following

       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 in-
              dices of ptys allocated in this new instance are independent  of
              indices created in other instances of devpts.

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

              This option is mainly used to support containers  in  the  linux
              kernel.   It  is  implemented  in linux kernel versions starting
              with 2.6.29.  Further, this mount option is valid only  if  CON-
              FIG_DEVPTS_MULTIPLE_INSTANCES  is enabled in the kernel configu-

              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 filesys-

              With  the  support  for multiple instances of devpts (see newin-
              stance option above), each instance has a private ptmx  node  in
              the root of the devpts filesystem (typically /dev/pts/ptmx).

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

              This option is only implemented in linux kernel versions  start-
              ing  with  2.6.29.   Further,  this option is valid only if CON-
              FIG_DEVPTS_MULTIPLE_INSTANCES is enabled in the kernel  configu-

   Mount options for fat
       (Note:  fat  is not a separate filesystem, but a common part of the ms-
       dos, 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 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 pickiness can be chosen:

                     Upper and lower case are accepted  and  equivalent,  long
                     name  parts  are  truncated (e.g. verylongname.foobar be-
                     comes, leading and embedded spaces are  ac-
                     cepted 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  spe-
                     cial  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 mod-
              ule 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 filesys-
              tem  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  configura-
              tion,  determined  by backing device size.  These static parame-
              ters match defaults assumed by DOS 1.x for 160 kiB, 180 kiB, 320
              kiB, and 360 kiB floppies and floppy images.

              Specify FAT behavior on critical errors: panic, continue without
              doing anything, or remount the partition in read-only mode  (de-
              fault 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 spu-
              rious ESTALE errors.

              nostale_ro:  This  option bases the inode number and file handle
              on the on-disk location of a file in the  FAT  directory  entry.
              This  ensures  that  ESTALE will not be returned after a file is
              evicted from the inode cache.  However, it means that operations
              such  as rename, create and unlink could cause file handles that
              previously pointed at one file to point at a different file, po-
              tentially causing data corruption.  For this reason, this option
              also mounts the filesystem readonly.

              To maintain backward compatibility, '-o nfs' is  also  accepted,
              defaulting to stale_rw.

       tz=UTC This  option disables the conversion of timestamps between local
              time (as used by Windows on FAT) and UTC (which Linux  uses  in-
              ternally).   This  is  particularly useful when mounting devices
              (like digital cameras) that are set to UTC in order to avoid the
              pitfalls of local time.

              Set  offset for conversion of timestamps from local time used by
              FAT to UTC.  I.e., minutes will be subtracted  from  each  time-
              stamp  to  convert  it to UTC used internally by Linux.  This is
              useful when the time zone set in the kernel via  settimeofday(2)
              is not the time zone used by the filesystem.  Note that this op-
              tion still does not provide correct time stamps in all cases  in
              presence of DST - time stamps in a different DST setting will be
              off by one hour.

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

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

              If you want to use ATTR_RO as read-only flag even for the direc-
              tory, 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 de-
              cision to the CDROM driver.  This option will fail with anything
              but a CDROM as underlying device.

       part=n Select partition number n from the device.  Only makes sense for
              CDROMs.  Defaults to not parsing the partition table at all.

       quiet  Don't complain about invalid mount options.

   Mount options for hpfs
       uid=value and gid=value
              Set  the owner and group of all files. (Default: the UID and GID
              of the current process.)

              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 re-
       strictions on filename length), and in addition all characters  are  in
       upper  case.   Also  there  is no field for file ownership, protection,
       number of links, provision for block/character devices, etc.

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

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

              Disable  the  use of Microsoft Joliet extensions, even if avail-
              able.  Cf. map.

              With check=relaxed, a filename is first converted to lower  case
              before  doing  the lookup.  This is probably only meaningful to-
              gether with norock and map=normal.  (Default: check=strict.)

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

              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  exten-

              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 key-
              word 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  op-
              tion to remount a volume where the nointegrity option was previ-
              ously specified in order to restore normal behavior.

              Define the behavior when an error is encountered.   (Either  ig-
              nore errors and just mark the filesystem erroneous and continue,
              or remount the filesystem read-only, or panic and halt the  sys-

              These options are accepted but ignored.

   Mount options for msdos
       See  mount  options for fat.  If the msdos filesystem detects an incon-
       sistency, it reports an error and sets the file system read-only.   The
       filesystem can be made writable again by remounting it.

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

   Mount options for ntfs
              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  un-
              known  Unicode characters.  For 1 (or `yes' or `true') or 2, use
              vfat-style 4-byte escape sequences starting with  ":".   Here  2
              give  a little-endian encoding and 1 a byteswapped bigendian en-

              If enabled (posix=1), the filesystem distinguishes between upper
              and lower case.  The 8.3 alias names are presented as hard links
              instead of being suppressed.  This option is obsolete.

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

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

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

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

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

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

              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 filesys-
              tem as upperdir.

   Mount options for reiserfs
       Reiserfs is a journaling filesystem.

       conv   Instructs version 3.6 reiserfs software to mount a  version  3.5
              filesystem,  using  the  3.6  format  for newly created objects.
              This filesystem will no longer be compatible with  reiserfs  3.5

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

                     A hash invented by Yury Yu. Rupasov.  It is fast and pre-
                     serves  locality,  mapping  lexicographically  close file
                     names to close hash values.  This option  should  not  be
                     used, as it causes a high probability of hash collisions.

              tea    A    Davis-Meyer    function    implemented   by   Jeremy
                     Fitzhardinge.  It uses hash permuting bits in  the  name.
                     It  gets  high randomness and, therefore, low probability
                     of hash collisions at some CPU cost.  This may be used if
                     EHASHCOLLISION errors are experienced with the r5 hash.

              r5     A  modified  version  of the rupasov hash.  It is used by
                     default and is the best choice unless the filesystem  has
                     huge directories and unusual file-name patterns.

              detect Instructs  mount  to detect which hash function is in use
                     by examining the filesystem being mounted, and  to  write
                     this  information  into the reiserfs superblock.  This is
                     only useful on the first mount of an old format  filesys-

              Tunes  the  block  allocator.   This may provide performance im-
              provements in some situations.

              Tunes the block allocator.  This  may  provide  performance  im-
              provements in some situations.

              Disable  the border allocator algorithm invented by Yury Yu. Ru-
              pasov.  This may provide performance improvements in some situa-

       nolog  Disable  journaling.   This  will provide slight performance im-
              provements in some situations at the cost of  losing  reiserfs's
              fast  recovery  from  crashes.  Even with this option turned on,
              reiserfs still performs all journaling operations, save for  ac-
              tual  writes  into its journaling area.  Implementation of nolog
              is a work in progress.

       notail By default, reiserfs stores small files  and  `file  tails'  di-
              rectly  into  its  tree.   This  confuses some utilities such as
              LILO(8).  This option is used to disable packing of  files  into
              the tree.

              Replay the transactions which are in the journal, but do not ac-
              tually mount the filesystem.  Mainly used by reiserfsck.

              A remount option which permits online expansion of reiserfs par-
              titions.   Instructs reiserfs to assume that the device has num-
              ber blocks.  This option is designed for use with devices  which
              are  under  logical volume management (LVM).  There is a special
              resizer    utility    which     can     be     obtained     from

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

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

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

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

       The device name may be specified as
              ubiX_Y UBI device number X, volume number Y

              ubiY   UBI device number 0, volume number Y

                     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 OSTA, the  Op-
       tical  Storage  Technology  Association, and is often used for DVD-ROM,
       frequently in the form of a hybrid UDF/ISO-9660 filesystem. It is, how-
       ever, perfectly usable by itself on disk drives, flash drives and other
       block devices.  See also iso9660.

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

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

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

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

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

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

              For other details see the mkudffs(8) 2.0+ manpage, sections COM-
              PATIBILITY and BLOCK SIZE.

       unhide Show otherwise hidden files.

              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 any-

              Select the session number for multi-session recorded optical me-
              dia. (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 re-
              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

              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 op-
       tion is explicitly killed by vfat.  Furthermore, there are

              Translate unhandled Unicode characters to  special  escaped  se-
              quences.   This  lets  you backup and restore filenames that are
              created with any Unicode characters.  Without this option, a '?'
              is  used  when no translation is possible.  The escape character
              is ':' because it is otherwise invalid on the  vfat  filesystem.
              The escape sequence that gets used, where u is the Unicode char-
              acter, is: ':', (u & 0x3f), ((u>>6) & 0x3f), (u>>12).

       posix  Allow two files with names that only differ in case.   This  op-
              tion is obsolete.

              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  de-
                     fault since Linux 2.6.32.

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

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

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

DM-VERITY SUPPORT (experimental)
       The device-mapper verity target provides read-only  transparent  integ-
       rity checking of block devices using kernel crypto API.  The mount com-
       mand can open the dm-verity device and do  the  integrity  verification
       before  on  the  device  filesystem is mounted.  Requires libcryptsetup
       with in libmount.  If libcryptsetup supports extracting the  root  hash
       of  an  already  mounted device, existing devices will be automatically
       reused in case of a match.  Mount options for dm-verity:

              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 ex-
              clusive with verity.roothashfile.

              Path to file containing the hex-encoded hash of the root of ver-
              ity.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  (de-
              fault: 0) is used by dm-verity to get to the FEC area. Optional.

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

       Supported since util-linux v2.35.

       For example commands:

              mksquashfs /etc /tmp/etc.squashfs
              dd if=/dev/zero of=/tmp/etc.hash bs=1M count=10
              veritysetup format /tmp/etc.squashfs /tmp/etc.hash
              mount -o verity.hashdevice=/tmp/etc.hash,verity.roothash=<hash> /tmp/etc.squashfs /mnt

       create squashfs image from /etc directory, verity hash device and mount
       verified filesystem image to /mnt.

       One further possible type is a mount via the loop device.  For example,
       the command

              mount /tmp/disk.img /mnt -t vfat -o loop=/dev/loop3

       will  set  up  the  loop  device  /dev/loop3  to correspond to the file
       /tmp/disk.img, and then mount this device on /mnt.

       If no explicit loop device is mentioned (but just an option  `-o  loop'
       is  given), then mount will try to find some unused loop device and use
       that, for example

              mount /tmp/disk.img /mnt -o loop

       The mount command automatically creates a loop device  from  a  regular
       file  if  a filesystem type is not specified or the filesystem is known
       for libblkid, for example:

              mount /tmp/disk.img /mnt

              mount -t ext4 /tmp/disk.img /mnt

       This type of mount knows about three options, namely loop,  offset  and
       sizelimit,  that  are really options to losetup(8).  (These options can
       be used in addition to those specific to the filesystem type.)

       Since Linux 2.6.25 auto-destruction of loop devices is supported, mean-
       ing that any loop device allocated by mount will be freed by umount in-
       dependently of /etc/mtab.

       You can also free a loop device by hand, using losetup -d or umount -d.

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

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

       0      success

       1      incorrect invocation or permissions

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

       4      internal mount bug

       8      user interrupt

       16     problems writing or locking /etc/mtab

       32     mount failure

       64     some mount succeeded

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

       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,  runbind-
       able,  private, rprivate, slave, rslave, shared, rshared, auto, noauto,
       comment, x-*, loop, offset and sizelimit to the mount.<suffix> helpers.
       All other options are used in a comma-separated list as argument to the
       -o option.

       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

       /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

              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

       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)

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

       Some Linux filesystems don't support -o sync nor -o dirsync (the  ext2,
       ext3,  ext4, fat and vfat filesystems do support synchronous updates (a
       la BSD) when mounted with the sync option).

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

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

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

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

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

       Karel Zak <>

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

util-linux                        August 2015                         MOUNT(8)

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