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 maybe 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  kernel
       and  it  is  usually  specific  to  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 name of disk partitions are unstable; hardware reconfigura-
       tion, 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> 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.

       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 maybe 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 /foox
              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.

              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.

       -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 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 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   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  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-

       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).  The optional ar-
              gument  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.

       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(5) 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.

       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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