mount(8)



MOUNT(8)                     System Administration                    MOUNT(8)

NAME
       mount - mount a filesystem

SYNOPSIS
       mount [-l|-h|-V]

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

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

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

DESCRIPTION
       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
       services.

       The standard form of the mount command is:

              mount -t type device dir

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

              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 knuth.cwi.nl:/dir.  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
       really  unique,  especially if you move, share or copy the device.  Use
       lsblk -o +UUID,PARTUUID to verify that the UUIDs are really  unique  in
       your system.

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

       Note that mount(8) uses UUIDs as strings.  The UUIDs from  the  command
       line  or from fstab(5) are not converted to internal binary 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
       options)  to  be mounted as indicated, except for those whose line con-
       tains 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.  This real mtab file
       is still supported, but on current Linux systems it is better  to  make
       it a symlink to /proc/mounts instead, because a regular mtab file main-
       tained in userspace cannot reliably work  with  namespaces,  containers
       and other advanced Linux features.

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

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

              mount device|dir -o options

       and  then  the  mount options from the command line will be appended to
       the list of options from /etc/fstab.  The usual behavior  is  that  the
       last option wins if there are conflicting ones.

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

              mount /dev/foo /dir

   Non-superuser mounts
       Normally,  only  the  superuser  can  mount filesystems.  However, when
       fstab contains the user option on a line, anybody can mount the  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
       directory, for example:

              mount --bind foo foo

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

              mount --rbind olddir newdir

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

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

              mount -o bind,ro foo foo

       This feature is not supported by the Linux kernel; it is implemented in
       userspace by an additional mount(2) remounting system call.  This 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
       entry),  but the original filesystem superblock will still be writable,
       meaning that the olddir will be writable, but the newdir will be  read-
       only.

       It's also possible to change nosuid, nodev, noexec, noatime, nodiratime
       and relatime VFS entry flags by "remount,bind" operation. It's impossi-
       ble to change mount options recursively (for example with -o rbind,ro).

       mount(8)  since  v2.31 ignores the bind flag from /etc/fstab on remount
       operation (if "-o remount" specified on command line). This  is  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
       impossible to re-define mount options without interaction with the bind
       semantic. This  mount(8)  behavior  does  not  affect  situations  when
       "remount,bind" is specified in the /etc/fstab file.

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

              mount --move olddir newdir

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

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

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

COMMAND-LINE OPTIONS
       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
              absolute  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
              devices or different NFS servers  in  parallel.   This  has  the
              advantage  that  it is faster; also NFS timeouts go in parallel.
              A disadvantage is that the mounts are done in  undefined  order.
              Thus,  you cannot use this option if you want to mount both /usr
              and /usr/spool.

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

       -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
              rest.

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

                     mount -a -t ext2 -O _netdev

              mounts  all  ext2  filesystems  with the _netdev option, not all
              filesystems that are either ext2  or  have  the  _netdev  option
              specified.

       -o, --options opts
              Use  the specified mount options.  The opts argument is a comma-
              separated list.  For example:

                     mount LABEL=mydisk -o noatime,nodev,nosuid

              For more details, see the FILESYSTEM-INDEPENDENT  MOUNT  OPTIONS
              and FILESYSTEM-SPECIFIC MOUNT OPTIONS sections.

       -R, --rbind
              Remount  a subtree and all possible submounts somewhere else (so
              that its contents are available in both places).  See above, the
              subsection Bind mounts.

       -r, --read-only
              Mount the filesystem read-only.  A synonym is -o ro.

              Note  that,  depending  on the filesystem type, state and kernel
              behavior, the system may still write to the device.   For  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
              options or set the block device itself to  read-only  mode,  see
              the blockdev(8) command.

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

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

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

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

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

       -t, --types fstype
              The argument following the -t is used to indicate the filesystem
              type.  The filesystem types which are currently supported depend
              on the running  kernel.   See  /proc/filesystems  and  /lib/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#example.com' 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
              entry.

              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
              default.  A synonym is -o rw.

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

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

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

FILESYSTEM-INDEPENDENT MOUNT OPTIONS
       Some  of  these  options  are  only  useful  when  they  appear  in the
       /etc/fstab file.

       Some of these options could be enabled or disabled by  default  in  the
       system  kernel.   To  check  the  current  setting  see  the options in
       /proc/mounts.  Note that filesystems also have per-filesystem  specific
       default  mount  options  (see  for  example  tune2fs -l output for extN
       filesystems).

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

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

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

       noatime
              Do  not  update  inode access times on this filesystem (e.g. for
              faster access on the news spool to speed up news servers).  This
              works  for  all  inode  types  (directories  too), so it implies
              nodiratime.

       auto   Can be mounted with the -a option.

       noauto Can only be mounted explicitly (i.e., the  -a  option  will  not
              cause the filesystem to be mounted).

       context=context, fscontext=context, defcontext=context, and
       rootcontext=context
              The context= option is useful when mounting filesystems that  do
              not  support  extended attributes, such as a floppy or hard disk
              formatted with VFAT, or systems that are  not  normally  running
              under SELinux, such as an ext3 formatted disk from a non-SELinux
              workstation.  You can also use context= on  filesystems  you  do
              not  trust,  such  as  a floppy.  It also helps in compatibility
              with xattr-supporting filesystems on earlier 2.4.<x> kernel ver-
              sions.   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
              context="system_u:object_r:removable_t".

              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
              using  defcontext=  option.   This  overrides  the value set for
              unlabeled files in the policy and  requires  a  filesystem  that
              supports xattr labeling.

              The  rootcontext= option allows you to explicitly label the root
              inode of a FS being mounted before that FS or inode becomes 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-
              text.

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

                     mount -t tmpfs none /mnt -o \
                       'context="system_u:object_r:tmp_t:s0:c127,c456",noexec'

              For more details, see selinux(8).

       defaults
              Use the default options: rw, suid, dev, exec, auto, nouser,  and
              async.

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

       dev    Interpret character or block special devices on the filesystem.

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

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

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

       dirsync
              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
              filesystem.

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

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

       noiversion
              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.

       _netdev
              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.

       relatime
              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
              modified.)

              Since Linux 2.6.30, the kernel defaults to the behavior provided
              by   this   option  (unless  noatime  was  specified),  and  the
              strictatime option is required to obtain traditional  semantics.
              In  addition, since Linux 2.6.30, the file's last access time is
              always updated if it is more than 1 day old.

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

       strictatime
              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.

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

       lazytime
              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
              disk.

       nolazytime
              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).

       remount
              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
              specified.

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

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

                  mount -o remount,rw  /dir

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

       ro     Mount the filesystem read-only.

       rw     Mount the filesystem read-write.

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

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

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

       users  Allow any user to mount and to unmount the filesystem, even when
              some  other  ordinary  user mounted it.  This option implies the
              options noexec, nosuid, and nodev (unless overridden  by  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
              another  operations.   Note  that maintain mount options in user
              space is tricky, because it's necessary use libmount based tools
              and there is no guarantee that the options will be always avail-
              able (for example after a move mount operation  or  in  unshared
              namespace).

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

       X-mount.mkdir[=mode]
              Allow to make a target  directory  (mountpoint).   The  optional
              argument  mode  specifies  the  filesystem  access mode used for
              mkdir(2) in octal notation.  The default  mode  is  0755.   This
              functionality  is  supported only for root users.  The option is
              also supported as x-mount.mkdir, this notation is deprecated for
              mount.mkdir since v2.30.

FILESYSTEM-SPECIFIC MOUNT OPTIONS
       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-
       tion/filesystems.

   Mount options for adfs
       uid=value and gid=value
              Set the owner and group of the files in the filesystem (default:
              uid=gid=0).

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

   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.

       mode=value
              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.

       protect
              Do not allow any changes to the protection bits on the  filesys-
              tem.

       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...

       verbose
              Print an informational message for each successful mount.

       prefix=string
              Prefix used before volume name, when following a link.

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

       reserved=value
              (Default: 2.) Number of  unused  blocks  at  the  start  of  the
              device.

       root=value
              Give explicitly the location of the root block.

       bs=value
              Give blocksize.  Allowed values are 512, 1024, 2048, 4096.

       grpquota|noquota|quota|usrquota
              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
       options:

       uid=n, gid=n
              Set the owner and group of the mountpoint.

       mode=value
              Sets the mode of the mountpoint.

   Mount options for devpts
       The devpts filesystem is a pseudo filesystem, traditionally mounted  on
       /dev/pts.   In  order  to  acquire  a  pseudo terminal, a process opens
       /dev/ptmx; the number of the pseudo terminal is then made available  to
       the   process  and  the  pseudo  terminal  slave  can  be  accessed  as
       /dev/pts/<number>.

       uid=value and gid=value
              This sets the owner or the group of newly created  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.

       mode=value
              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.

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

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

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

              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.

       ptmxmode=value

              Set the mode for the new ptmx device node in the devpts filesys-
              tem.

              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-
              ration.

   Mount options for fat
       (Note:  fat  is  not  a  separate  filesystem, but a common part of the
       msdos, umsdos and vfat filesystems.)

       blocksize={512|1024|2048}
              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.)

       umask=value
              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.

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

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

       allow_utime=value
              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.

       check=value
              Three different levels of pickyness can be chosen:

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

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

              s[trict]
                     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.

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

       conv=mode
              This option is obsolete and may fail or being ignored.

       cvf_format=module
              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.

       cvf_option=option
              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).

       discard
              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.

       dos1xfloppy
              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.

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

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

       iocharset=value
              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.

       nfs={stale_rw|nostale_ro}
              Enable this only if you want to export the FAT  filesystem  over
              NFS.

              stale_rw:  This  option  maintains an index (cache) of directory
              inodes which is used by the nfs-related code  to  improve  look-
              ups.   Full  file operations (read/write) over NFS are supported
              but with cache eviction at NFS server, this could result in 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,
              potentially  causing  data  corruption.   For  this reason, this
              option also mounts the filesystem readonly.

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

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

       time_offset=minutes
              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
              option still does not provide correct time stamps in  all  cases
              in presence of DST - time stamps in a different DST setting will
              be off by one hour.

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

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

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

       showexec
              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.

       sys_immutable
              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.

       usefree
              Use  the  "free clusters" value stored on FSINFO.  It'll be used
              to determine number of free clusters without scanning disk.  But
              it's not used by default, because recent Windows don't update it
              correctly in some case.  If you are sure the "free clusters"  on
              FSINFO is correct, by this option you can avoid scanning disk.

       dots, nodots, dotsOK=[yes|no]
              Various misguided attempts to force Unix or DOS conventions onto
              a FAT filesystem.

   Mount options for hfs
       creator=cccc, type=cccc
              Set the creator/type values as shown by the  MacOS  finder  used
              for creating new files.  Default values: '????'.

       uid=n, gid=n
              Set the owner and group of all files.  (Default: the UID and GID
              of the current process.)

       dir_umask=n, file_umask=n, umask=n
              Set the umask used for all directories, all  regular  files,  or
              all files and directories.  Defaults to the umask of the current
              process.

       session=n
              Select the CDROM session to mount.   Defaults  to  leaving  that
              decision  to  the CDROM driver.  This option will fail with any-
              thing 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.)

       umask=value
              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.

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

       conv=mode
              This option is obsolete and may fail or being ignored.

       nocheck
              Do not abort mounting when certain consistency checks fail.

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

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

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

       check={r[elaxed]|s[trict]}
              With check=relaxed, a filename is first converted to lower  case
              before  doing  the  lookup.   This  is  probably only meaningful
              together with norock and map=normal.  (Default: check=strict.)

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

       map={n[ormal]|o[ff]|a[corn]}
              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.

       mode=value
              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.)

       block={512|1024|2048}
              Set  the  block  size  to  the   indicated   value.    (Default:
              block=1024.)

       conv=mode
              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.

       session=x
              Select number of session on multisession CD.

       sbsector=xxx
              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-
       sions.

       iocharset=value
              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
       iocharset=name
              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=value
              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
              partition.

       nointegrity
              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.

       integrity
              Default.  Commit metadata changes  to  the  journal.   Use  this
              option to remount a volume where the nointegrity option was pre-
              viously specified in order to restore normal behavior.

       errors={continue|remount-ro|panic}
              Define the behavior  when  an  error  is  encountered.   (Either
              ignore  errors  and  just mark the filesystem erroneous and con-
              tinue, or remount the filesystem read-only, or  panic  and  halt
              the system.)

       noquota|quota|usrquota|grpquota
              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
       iocharset=name
              Character set to use when returning file  names.   Unlike  VFAT,
              NTFS  suppresses  names  that contain nonconvertible characters.
              Deprecated.

       nls=name
              New name for the option earlier called iocharset.

       utf8   Use UTF-8 for converting file names.

       uni_xlate={0|1|2}
              For 0 (or `no' or `false'), do  not  use  escape  sequences  for
              unknown  Unicode  characters.   For 1 (or `yes' or `true') or 2,
              use vfat-style 4-byte escape sequences starting with ":".   Here
              2  give  a  little-endian encoding and 1 a byteswapped bigendian
              encoding.

       posix=[0|1]
              If enabled (posix=1), the filesystem distinguishes between upper
              and lower case.  The 8.3 alias names are presented as hard links
              instead of being suppressed.  This option is obsolete.

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

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

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

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

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

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

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

       upperdir=directory
              The upperdir is normally on a writable filesystem.

       workdir=directory
              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
              tools.

       hash={rupasov|tea|r5|detect}
              Choose  which  hash  function  reiserfs  will  use to find files
              within directories.

              rupasov
                     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-
                     tem.

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

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

       noborder
              Disable  the  border  allocator  algorithm  invented by Yury Yu.
              Rupasov.  This may provide performance improvements in some sit-
              uations.

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

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

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

       resize=number
              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
              ftp://ftp.namesys.com/pub/reiserfsprogs.

       user_xattr
              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
              (default).   This  also  requires  an IO stack which can support
              barriers, and if reiserfs gets an error on a barrier  write,  it
              will  disable  barriers  again  with  a warning.  Write barriers
              enforce proper  on-disk  ordering  of  journal  commits,  making
              volatile  disk  write  caches  safe  to use, at some performance
              penalty.  If  your  disks  are  battery-backed  in  one  way  or
              another, disabling barriers may safely improve performance.

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

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

              ubiY   UBI device number 0, volume number Y

              ubiX:NAME
                     UBI device number X, volume with name NAME

              ubi:NAME
                     UBI device number 0, volume with name NAME
       Alternative !  separator may be used instead of :.

       The following mount options are available:

       bulk_read
              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.

       no_bulk_read
              Do not bulk-read.  This is the default.

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

       no_chk_data_crc.
              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.

       compr={none|lzo|zlib}
              Select the default compressor which is used when new  files  are
              written.   It  is  still  possible  to  read compressed files if
              mounted with the none option.

   Mount options for udf
       UDF is the "Universal Disk Format"  filesystem  defined  by  OSTA,  the
       Optical  Storage Technology Association, and is often used for DVD-ROM,
       frequently in the form of a hybrid UDF/ISO-9660 filesystem. It is, 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
              addition to) uid=<user> and results in UDF not storing  uids  to
              the  media.  In fact the recorded uid is the 32-bit overflow uid
              -1 as defined by the UDF standard.  The value is given as either
              <user>  which  is a valid user name or the corresponding decimal
              user id, or the special string "forget".

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

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

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

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

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

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

       unhide Show otherwise hidden files.

       undelete
              Show deleted files in lists.

       adinicb
              Embed data in the inode. (default)

       noadinicb
              Don't embed data in the inode.

       shortad
              Use short UDF address descriptors.

       longad Use long UDF address descriptors. (default)

       nostrict
              Unset strict conformance.

       iocharset=
              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-
              way.

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

       anchor=
              Override standard anchor location. (default= 256)

       lastblock=
              Set the last block of the filesystem.

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

       gid=ignore
              Ignored, use gid=<group> instead.

       volume=
              Unimplemented and ignored.

       partition=
              Unimplemented and ignored.

       fileset=
              Unimplemented and ignored.

       rootdir=
              Unimplemented and ignored.

   Mount options for ufs
       ufstype=value
              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.

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

              nextstep-cd
                     For NextStep CDROMs (block_size == 2048), read-only.

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

       onerror=value
              Set behavior on error:

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

              [lock|umount|repair]
                     These mount options don't do anything at present; when an
                     error is encountered only a console message is printed.

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

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

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

       posix  Allow two files with names  that  only  differ  in  case.   This
              option is obsolete.

       nonumtail
              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.

       shortname=mode
              Defines the behavior for creation and display of filenames which
              fit into 8.3 characters.  If a long name for a file  exists,  it
              will  always  be  the preferred one for display.  There are four
              modes:

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

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

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

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

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

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

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

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

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

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

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

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

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

              mount /tmp/disk.img /mnt

              mount -t ext3 /tmp/disk.img /mnt

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

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

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

       Since util-linux v2.29 mount 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.

RETURN CODES
       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).

EXTERNAL HELPERS
       The syntax of external mount helpers is:

           /sbin/mount.suffix spec dir [-sfnv] [-o options] [-t type.subtype]

       where the suffix is the filesystem type and the -sfnvo options have the
       same  meaning  as  the normal mount options.  The -t option is used for
       filesystems with subtypes  support  (for  example  /sbin/mount.fuse  -t
       fuse.sshfs).

       The  command mount does not pass the mount options unbindable, 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.

FILES
       /etc/fstab        filesystem table

       /etc/mtab         table of mounted filesystems

       /etc/mtab~        lock file

       /etc/mtab.tmp     temporary file

       /etc/filesystems  a list of filesystem types to try

ENVIRONMENT
       LIBMOUNT_FSTAB=<path>
              overrides  the  default  location of the fstab file (ignored for
              suid)

       LIBMOUNT_MTAB=<path>
              overrides the default location of the  mtab  file  (ignored  for
              suid)

       LIBMOUNT_DEBUG=all
              enables libmount debug output

       LIBBLKID_DEBUG=all
              enables libblkid debug output

       LOOPDEV_DEBUG=all
              enables loop device setup debug output

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

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

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

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

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

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

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

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

AUTHORS
       Karel Zak <kzak@redhat.com>

AVAILABILITY
       The  mount  command  is part of the util-linux package and is available
       from https://www.kernel.org/pub/linux/utils/util-linux/.

util-linux                        August 2015                         MOUNT(8)

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