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       mount - mount a filesystem


       mount [-lhV]

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

       mount [-fnrsvw] [-o option[,option]...]  device|dir

       mount [-fnrsvw] [-t vfstype] [-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
       several  devices.   The  mount  command serves to attach the filesystem
       found on some device to the big file tree.  Conversely,  the  umount(8)
       command will detach it again.

       The 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 previous contents (if  any)
       and  owner  and  mode  of  dir  become  invisible,  and as long as this
       filesystem remains mounted, the pathname dir refers to the root of  the
       filesystem on device.

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

              mount /dir

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

              mount --target /mountpoint

       The listing.
              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

                     mount [-l] [-t type]

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

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

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

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

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

       The /etc/fstab, /etc/mtab and /proc/mounts files.
              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

              The command

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

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

              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  list  of
              currently  mounted  filesystems in the file /etc/mtab.  The mtab
              file is still supported, but it's recommended to use  a  symlink
              to  the  file  /proc/mounts rather than the regular mtab file on
              the  current  Linux  systems.   The  mtab  file  maintained   in
              userspace  cannot  reliably work with namespaces, containers and
              another advanced Linux features.

              If no arguments are given to mount, this list 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

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

                     mount /dev/foo /dir

       The non-superuser mounts.
              Normally, only the superuser can  mount  filesystems.   However,
              when fstab contains the user option on a line, anybody can mount
              the corresponding filesystem.

              Thus, given a line

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

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

                     mount /dev/cdrom


                     mount /cd

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

       The bind mounts.
              Since  Linux  2.4.0  it  is possible to remount part of the file
              hierarchy somewhere else.  The call is:

                     mount --bind olddir newdir

              or by using this fstab entry:

                     /olddir /newdir none bind

              After this call the same contents are accessible in two  places.
              One  can  also  remount  a single file (on a single file).  It's
              also possible to use the bind mount to create a mountpoint  from
              a regular directory, for example:

                     mount --bind foo foo

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

                     mount --rbind olddir newdir

              Note  that  the filesystem mount options will remain the same as
              those on the original mount point,  and  cannot  be  changed  by
              passing  the  -o  option  along  with --bind/--rbind.  The mount
              options can be  changed  by  a  separate  remount  command,  for

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

              Note  that  the behavior of the remount operation depends on the
              /etc/mtab file.  The first command stores the 'bind' flag in the
              /etc/mtab  file  and  the second command reads the flag from the
              file.  If you have a system without the /etc/mtab file or if you
              explicitly  define  source  and  target  for the remount command
              (then mount(8) does not read /etc/mtab), then you  have  to  use
              the  bind  flag  (or  option)  for the remount command too.  For

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

              Note that remount,ro,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.

       The move operation.
              Since  Linux  2.5.1  it is possible to atomically move a mounted
              tree to another place.  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

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

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

              Supported operations are:

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

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

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

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

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

              Since util-linux 2.23 the mount command allows  to  use  several
              propagation  flags  together  and also together with other mount
              operations.  This  feature  is  EXPERIMENTAL.   The  propagation
              flags  are  applied  by  additional  mount(2)  syscalls when the
              preceeding mount operations were successful.  Note that this use
              case  is  not atomic.  It is possible to specify the propagation
              flags in fstab(5) as  mount  options  (private,  slave,  shared,
              unbindable, rprivate, rslave, rshared, runbindable).

              For example:

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

              is the same as:

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


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

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

       Command-line options available for the mount command are:

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

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

       -v, --verbose
              Verbose mode.

       -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.

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

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

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

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

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

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

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

       -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 dev
              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 dir
              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.

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

              Note  that,  depending  on the filesystem type, state and kernel
              behavior, the  system  may  still  write  to  the  device.   For
              example, ext3 and ext4 will replay the journal if the filesystem
              is dirty.  To prevent this kind of write access, you may want to
              mount  an  ext3  or  ext4  filesystem  with  the ro,noload mount
              options or set the block device itself to  read-only  mode,  see
              the blockdev(8) command.

       -w, --rw, --read-write
              Mount  the  filesystem  read/write.   This  is  the  default.  A
              synonym is -o rw.

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

       -U, --uuid uuid
              Mount the partition that has  the  specified  uuid.   These  two
              options  require  the file /proc/partitions (present since Linux
              2.1.116) to exist.

       -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

              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 vfstype
              The argument following the -t is used to indicate the filesystem
              type.   The  filesystem  types  which  are  currently  supported
              include:  adfs,  affs,  autofs,  btrfs,  cifs,  coda,  coherent,
              cramfs,  debugfs,  devpts,  efs,  ext,  ext2,  ext3,  ext4, hfs,
              hfsplus, hpfs, iso9660, jfs, minix,  msdos,  ncpfs,  nfs,  nfs4,
              ntfs, proc, qnx4, ramfs, reiserfs, romfs, squashfs, smbfs, sysv,
              tmpfs, ubifs, udf, ufs, umsdos, usbfs, vfat, xenix, xfs,  xiafs.
              Note that coherent, sysv and xenix are equivalent and that xenix
              and coherent will be removed at some point in the future  –  use
              sysv  instead.   Since  kernel  version 2.1.21 the types ext and
              xiafs do  not  exist  anymore.   Earlier,  usbfs  was  known  as
              usbdevfs.   Note,  the  real  list  of all supported filesystems
              depends on your kernel.

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

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

              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.
              The  list of filesystem types can be prefixed with no to specify
              the filesystem types on which no action should be taken.   (This
              can be meaningful with the -a option.)  For example, the command

                     mount -a -t nomsdos,ext

              mounts all filesystems except those of type msdos and ext.

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

                     mount -a -O no_netdev

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

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

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

                     mount -a -t ext2 -O _netdev

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

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

                     mount LABEL=mydisk -o noatime,nodev,nosuid

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

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

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

       -M, --move
              Move a subtree to some other place.  See above.


       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, fat, vfat and ufs):

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

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

       auto   Can be mounted with the -a option.

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

       context=context,     fscontext=/context,     defcontext=/context    and
              The context= option is useful when mounting filesystems that  do
              not  support  extended attributes, such as a floppy or hard disk
              formatted with VFAT, or systems that are  not  normally  running
              under SELinux, such as an ext3 formatted disk from a non-SELinux
              workstation.  You can also use context= on  filesystems  you  do
              not  trust,  such  as  a floppy.  It also helps in compatibility
              with xattr-supporting  filesystems  on  earlier  2.4.<x>  kernel
              versions.   Even  where  xattrs are supported, you can save time
              not having to label every file by assigning the entire disk  one
              security context.

              A    commonly    used    option    for    removable   media   is

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

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

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

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

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

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

                     mount -t tmpfs none /mnt -o \

              For more details, see selinux(8).

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

              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.

              Do not update directory inode access times on this filesystem.

              All  directory  updates  within  the  filesystem  should be done
              synchronously.  This affects the following system calls:  creat,
              link, unlink, symlink, mkdir, rmdir, mknod and rename.

       exec   Permit execution of binaries.

       noexec Do  not  permit  direct execution of any binaries on the mounted
              filesystem.  (Until recently it was  possible  to  run  binaries
              anyway using a command like /lib/ld*.so /mnt/binary.  This trick
              fails since Linux 2.4.25 / 2.6.0.)

       group  Allow an ordinary (i.e., non-root) user to mount the  filesystem
              if  one  of  his  groups  matches the group of the device.  This
              option implies the options nosuid and nodev  (unless  overridden
              by subsequent options, as in the option line group,dev,suid).

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

              Do not increment the i_version inode field.

       mand   Allow mandatory locks on this filesystem.  See fcntl(2).

       nomand Do not allow mandatory locks on this filesystem.

              The filesystem resides on a device that requires network  access
              (used  to  prevent  the  system  from  attempting to mount these
              filesystems until the network has been enabled on the system).

       nofail Do not report errors for this device if it does not exist.

              Update inode access times relative to  modify  or  change  time.
              Access  time  is  only  updated  if the previous access time was
              earlier than the current modify or  change  time.   (Similar  to
              noatime,  but  it  doesn't break mutt or other applications that
              need to know if a file has been read since the last time it  was

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

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

              Allows to explicitly request full atime updates.  This makes  it
              possible  for  the  kernel to default to relatime or noatime but
              still allow userspace to override it.  For  more  details  about
              the default system mount options see /proc/mounts.

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

       suid   Allow  set-user-identifier  or set-group-identifier bits to take

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

       silent Turn on the silent flag.

       loud   Turn off the silent flag.

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

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

              The  remount  functionality  follows  the standard way the mount
              command works with options from  fstab.   This  means  that  the
              mount  command  only  doesn't read fstab (or mtab) when both the
              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  is ignored, except the loop= option which is
              internally generated and maintained by the mount command.

              mount -o remount,rw  /dir

              After this call mount reads fstab (or  mtab)  and  merges  these
              options with the options from the command line (-o).

       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 mtab (or  to  the  private  libmount
              file  in  /run/mount  on system without regular mtab) so that he
              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  (i.e.,  non-root)  user   to   mount   the
              filesystem.   This  is  the default; it does not imply any other

       users  Allow every user to mount  and  unmount  the  filesystem.   This
              option  implies  the  options  noexec, nosuid, and nodev (unless
              overridden  by  subsequent  options,  as  in  the  option   line

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

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

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

Mount options for adfs

       uid=value and gid=value
              Set the owner and group of the files in the filesystem (default:

       ownmask=value and othmask=value
              Set the permission mask for ADFS 'owner' permissions and 'other'
              permissions,    respectively    (default:    0700    and   0077,
              respectively).                      See                     also

Mount options for affs

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

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

              Set  the  mode  of  all  files  to value & 0777 disregarding the
              original permissions.  Add search permission to directories that
              have read permission.  The value is given in octal.

              Do  not  allow  any  changes  to  the  protection  bits  on  the

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

              Print an informational message for each successful mount.

              Prefix used before volume name, when following a link.

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

              (Default:  2.)  Number  of  unused  blocks  at  the start of the

              Give explicitly the location of the root block.

              Give blocksize.  Allowed values are 512, 1024, 2048, 4096.

              These  options  are  accepted  but  ignored.   (However,   quota
              utilities may react to such strings in /etc/fstab.)

Mount options for btrfs

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              Enable/disable the  tree  logging  used  for  fsync  and  O_SYNC

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

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

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

              Disable freespace cache loading without clearing the cache.

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

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

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

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

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

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

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

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

Mount options for cifs

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

Mount options for coherent


Mount options for debugfs

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

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

              Sets the mode of the mountpoint.

Mount options for devpts

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

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

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

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

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

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

              To use this option effectively, /dev/ptmx  must  be  a  symbolic
              link  to  pts/ptmx.  See Documentation/filesystems/devpts.txt in
              the linux kernel source tree for details.


              Set the mode  for  the  new  ptmx  device  node  in  the  devpts

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

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

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

Mount options for ext

       None.   Note  that  the  `ext'  filesystem  is obsolete.  Don't use it.
       Since Linux version 2.1.21 extfs  is  no  longer  part  of  the  kernel

Mount options for ext2

       The  `ext2'  filesystem  is the standard Linux filesystem.  Since Linux
       2.5.46, for most  mount  options  the  default  is  determined  by  the
       filesystem superblock.  Set them with tune2fs(8).

              Support POSIX Access Control Lists (or not).

              Set  the  behavior  for  the  statfs  system  call.  The minixdf
              behavior is to return in the f_blocks field the total number  of
              blocks of the filesystem, while the bsddf behavior (which is the
              default) is to subtract the overhead blocks  used  by  the  ext2
              filesystem and not available for file storage.  Thus

              % mount /k -o minixdf; df /k; umount /k

              Filesystem  1024-blocks   Used  Available  Capacity  Mounted on
              /dev/sda6     2630655    86954   2412169      3%     /k

              % mount /k -o bsddf; df /k; umount /k

              Filesystem  1024-blocks  Used  Available  Capacity  Mounted on
              /dev/sda6     2543714      13   2412169      0%     /k

              (Note  that  this  example  shows  that one can add command-line
              options to the options given in /etc/fstab.)

       check=none or nocheck
              No checking is done at mount time.  This is the  default.   This
              is  fast.   It  is  wise to invoke e2fsck(8) every now and then,
              e.g. at boot time.   The  non-default  behavior  is  unsupported
              (check=normal and check=strict options have been removed).  Note
              that these mount options don't have  to  be  supported  if  ext4
              kernel driver is used for ext2 and ext3 filesystems.

       debug  Print debugging info upon each (re)mount.

              Define  the  behavior  when  an  error  is encountered.  (Either
              ignore  errors  and  just  mark  the  filesystem  erroneous  and
              continue, or remount the filesystem read-only, or panic and halt
              the system.)  The default is set in the  filesystem  superblock,
              and can be changed using tune2fs(8).

       grpid|bsdgroups and nogrpid|sysvgroups
              These  options  define  what group id a newly created file gets.
              When grpid is set, it takes the group id  of  the  directory  in
              which  it is created; otherwise (the default) it takes the fsgid
              of the current process, unless the directory has the setgid  bit
              set,  in  which case it takes the gid from the parent directory,
              and also gets the setgid bit set if it is a directory itself.

              The usrquota (same as quota) mount  option  enables  user  quota
              support  on  the  filesystem.   grpquota  enables  group  quotas
              support.  You need the quota utilities to  actually  enable  and
              manage the quota system.

              Disables  32-bit  UIDs  and  GIDs.  This is for interoperability
              with older kernels which only store and expect 16-bit values.

       oldalloc or orlov
              Use old allocator or Orlov allocator for new inodes.   Orlov  is

       resgid=n and resuid=n
              The  ext2  filesystem  reserves  a  certain  percentage  of  the
              available space (by default 5%, see mke2fs(8)  and  tune2fs(8)).
              These  options  determine  who  can  use  the  reserved  blocks.
              (Roughly: whoever has the  specified  uid,  or  belongs  to  the
              specified group.)

       sb=n   Instead  of  block  1, use block n as superblock.  This could be
              useful when the filesystem has been damaged.   (Earlier,  copies
              of  the  superblock would be made every 8192 blocks: in block 1,
              8193, 16385, ... (and one got  thousands  of  copies  on  a  big
              filesystem).   Since  version  1.08,  mke2fs  has  a  -s (sparse
              superblock) option to reduce the number of  backup  superblocks,
              and  since version 1.15 this is the default.  Note that this may
              mean that ext2 filesystems created by a recent mke2fs cannot  be
              mounted  r/w under Linux 2.0.*.)  The block number here uses 1 k
              units.  Thus, if you want  to  use  logical  block  32768  on  a
              filesystem with 4 k blocks, use "sb=131072".

              Support "user." extended attributes (or not).

Mount options for ext3

       The  ext3 filesystem is a version of the ext2 filesystem which has been
       enhanced with journaling.  It supports the same options as ext2 as well
       as the following additions:

              Update the ext3 filesystem's journal to the current format.

              When   a   journal  already  exists,  this  option  is  ignored.
              Otherwise, it specifies the  number  of  the  inode  which  will
              represent the ext3 filesystem's journal file; ext3 will create a
              new journal, overwriting the old  contents  of  the  file  whose
              inode number is inum.

              When  the  external  journal  device's  major/minor numbers have
              changed, these options allow the user to specify the new journal
              location.   The  journal device is identified either through its
              new major/minor numbers encoded in devnum, or via a path to  the

              Don't load the journal on mounting.  Note that if the filesystem
              was not unmounted cleanly, skipping the journal replay will lead
              to  the  filesystem  containing inconsistencies that can lead to
              any number of problems.

              Specifies the journaling mode for file data.  Metadata is always
              journaled.   To  use  modes  other  than  ordered  on  the  root
              filesystem, pass the mode to the kernel as boot parameter,  e.g.

                     All  data  is  committed  into the journal prior to being
                     written into the main filesystem.

                     This is the default mode.  All data  is  forced  directly
                     out  to  the main file system prior to its metadata being
                     committed to the journal.

                     Data ordering is not preserved – data may be written into
                     the main filesystem after its metadata has been committed
                     to the journal.  This is  rumoured  to  be  the  highest-
                     throughput  option.   It  guarantees  internal filesystem
                     integrity, however it can allow old  data  to  appear  in
                     files after a crash and journal recovery.

              Just  print  an  error message if an error occurs in a file data
              buffer in ordered mode.

              Abort the journal if an error occurs in a file  data  buffer  in
              ordered mode.

       barrier=0 / barrier=1
              This  disables  /  enables  the use of write barriers in the jbd
              code.  barrier=0 disables, barrier=1  enables  (default).   This
              also requires an IO stack which can support barriers, and if jbd
              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.

              Sync  all  data  and  metadata every nrsec seconds.  The default
              value is 5 seconds.  Zero means default.

              Enable Extended User Attributes.  See the attr(5) manual page.

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

              Apart from the old quota system (as in  ext2,  jqfmt=vfsold  aka
              version  1 quota) ext3 also supports journaled quotas (version 2
              quota).  jqfmt=vfsv0 enables journaled  quotas.   For  journaled
              quotas    the    mount    options    usrjquota=aquota.user   and
     are required to  tell  the  quota  system
              which  quota  database  files to use.  Journaled quotas have the
              advantage that even after a crash no quota check is required.

Mount options for ext4

       The ext4 filesystem is an advanced level of the ext3  filesystem  which
       incorporates  scalability  and  reliability enhancements for supporting
       large filesystem.

       The options  journal_dev,  norecovery,  noload,  data,  commit,  orlov,
       oldalloc,   [no]user_xattr  [no]acl,  bsddf,  minixdf,  debug,  errors,
       data_err, grpid, bsdgroups, nogrpid  sysvgroups,  resgid,  resuid,  sb,
       quota,  noquota,  grpquota, usrquota usrjquota, grpjquota and jqfmt are
       backwardly compatible with ext3 or ext2.

              Enable checksumming of  the  journal  transactions.   This  will
              allow  the  recovery  code  in  e2fsck  and the kernel to detect
              corruption in the kernel.  It is a compatible change and will be
              ignored by older kernels.

              Commit  block  can  be  written  to  disk  without  waiting  for
              descriptor blocks.  If enabled, older kernels cannot  mount  the
              device.  This will enable 'journal_checksum' internally.

       barrier=0 / barrier=1 / barrier / nobarrier
              These  mount options have the same effect as in ext3.  The mount
              options "barrier" and "nobarrier" are added for consistency with
              other ext4 mount options.

              The ext4 filesystem enables write barriers by default.

              This tuning parameter controls the maximum number of inode table
              blocks that ext4's inode table readahead algorithm will pre-read
              into  the  buffer  cache.   The value must be a power of 2.  The
              default value is 32 blocks.

              Number of filesystem blocks that mballoc will  try  to  use  for
              allocation  size and alignment.  For RAID5/6 systems this should
              be the number of data disks *  RAID  chunk  size  in  filesystem

              Deferring block allocation until write-out time.

              Disable  delayed  allocation.  Blocks are allocated when data is
              copied from user to page cache.

              Maximum  amount  of  time  ext4  should  wait   for   additional
              filesystem  operations  to  be batch together with a synchronous
              write operation.  Since a synchronous write operation  is  going
              to  force  a  commit  and  then  a wait for the I/O complete, it
              doesn't cost much, and can be a huge throughput win, we wait for
              a  small  amount  of  time  to see if any other transactions can
              piggyback on the  synchronous  write.   The  algorithm  used  is
              designed  to  automatically  tune  for the speed of the disk, by
              measuring the amount of time  (on  average)  that  it  takes  to
              finish  committing  a  transaction.   Call this time the "commit
              time".  If the time that the transaction  has  been  running  is
              less than the commit time, ext4 will try sleeping for the commit
              time to see if other operations will join the transaction.   The
              commit  time  is capped by the max_batch_time, which defaults to
              15000 µs (15 ms).  This optimization can be turned off  entirely
              by setting max_batch_time to 0.

              This  parameter  sets the commit time (as described above) to be
              at least min_batch_time.   It  defaults  to  zero  microseconds.
              Increasing  this  parameter may improve the throughput of multi-
              threaded, synchronous workloads on very fast disks, at the  cost
              of increasing latency.

              The  I/O priority (from 0 to 7, where 0 is the highest priority)
              which should be used for I/O operations submitted by  kjournald2
              during  a  commit  operation.   This  defaults  to 3, which is a
              slightly higher priority than the default I/O priority.

       abort  Simulate the  effects  of  calling  ext4_abort()  for  debugging
              purposes.   This  is normally used while remounting a filesystem
              which is already mounted.

              Many  broken  applications  don't  use  fsync()  when  replacing
              existing files via patterns such as

              fd  = open("")/write(fd,...)/close(fd)/ rename("",

              or worse yet

              fd = open("foo", O_TRUNC)/write(fd,...)/close(fd).

              If auto_da_alloc is enabled, ext4 will detect  the  replace-via-
              rename  and  replace-via-truncate  patterns  and  force that any
              delayed allocation blocks are allocated such that  at  the  next
              journal  commit,  in  the  default  data=ordered  mode, the data
              blocks of the new file are forced to disk  before  the  rename()
              operation is committed.  This provides roughly the same level of
              guarantees as ext3, and avoids the  "zero-length"  problem  that
              can  happen  when a system crashes before the delayed allocation
              blocks are forced to disk.

              Do not initialize any uninitialized inode table  blocks  in  the
              background.   This  feature  may be used by installation CD's so
              that the install process can complete as  quickly  as  possible;
              the  inode  table  initialization process would then be deferred
              until the next time the filesystem is mounted.

              The lazy itable init code  will  wait  n  times  the  number  of
              milliseconds  it  took  to  zero  out the previous block group's
              inode table.  This minimizes the impact  on  system  performance
              while the filesystem's inode table is being initialized.

              Controls  whether ext4 should issue discard/TRIM commands to the
              underlying block device when blocks are freed.  This  is  useful
              for  SSD  devices  and sparse/thinly-provisioned LUNs, but it is
              off by default until sufficient testing has been done.

              Disables 32-bit UIDs and GIDs.   This  is  for  interoperability
              with older kernels which only store and expect 16-bit values.

              This  options  allows to enables/disables the in-kernel facility
              for tracking filesystem metadata  blocks  within  internal  data
              structures.    This   allows  multi-block  allocator  and  other
              routines to quickly locate  extents  which  might  overlap  with
              filesystem   metadata  blocks.   This  option  is  intended  for
              debugging  purposes  and  since  it   negatively   affects   the
              performance, it is off by default.

              Controls  whether  or  not ext4 should use the DIO read locking.
              If the dioread_nolock option is  specified  ext4  will  allocate
              uninitialized  extent before buffer write and convert the extent
              to initialized after IO completes.  This  approach  allows  ext4
              code  to  avoid using inode mutex, which improves scalability on
              high speed storages.  However  this  does  not  work  with  data
              journaling and dioread_nolock option will be ignored with kernel
              warning.  Note that dioread_nolock code path is  only  used  for
              extent-based  files.   Because  of the restrictions this options
              comprises it is off by default (e.g. dioread_lock).

              This limits the size of the directories so that any  attempt  to
              expand  them  beyond the specified limit in kilobytes will cause
              an  ENOSPC  error.   This  is   useful   in   memory-constrained
              environments,  where  a  very  large  directory can cause severe
              performance problems or even provoke the Out Of  Memory  killer.
              (For example, if there is only 512 MB memory available, a 176 MB
              directory may seriously cramp the system's style.)

              Enable 64-bit inode version support.   This  option  is  off  by

Mount options for fat

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

              Set blocksize (default 512).  This option is obsolete.

       uid=value and gid=value
              Set the owner and group of all files.  (Default: the uid and gid
              of the current process.)

              Set  the  umask  (the  bitmask  of  the permissions that are not
              present).  The default is the umask of the current process.  The
              value is given in octal.

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

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

              This option controls the permission check of mtime/atime.

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

              2      Other users can change timestamp.

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

              Normally  utime(2)  checks 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
                     becomes, leading and  embedded  spaces  are
                     accepted in each name part (name and extension).

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

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

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

              The  fat  filesystem  can  perform CRLF<-->NL conversion (MS-DOS
              text format to UNIX text format) in the kernel.   The  following
              conversion modes are available:

                     No translation is performed.  This is the default.

              t[ext] CRLF<-->NL translation is performed on all files.

              a[uto] CRLF<-->NL  translation  is  performed  on all files that
                     don't have a "well-known binary" extension.  The list  of
                     known  extensions  can  be  found  at  the  beginning  of
                     fs/fat/misc.c (as of 2.0, the list  is:  exe,  com,  bin,
                     app,  sys,  drv,  ovl, ovr, obj, lib, dll, pif, arc, zip,
                     lha, lzh, zoo, tar, z, arj, tz, taz, tzp, tpz,  gz,  tgz,
                     deb,  gif,  bmp, tif, gl, jpg, pcx, tfm, vf, gf, pk, pxl,

              Programs that do  computed  lseeks  won't  like  in-kernel  text
              conversion.   Several  people have had their data ruined by this
              translation.  Beware!

              For filesystems  mounted  in  binary  mode,  a  conversion  tool
              (fromdos/todos) is available.  This option is obsolete.

              Forces the driver to use the CVF (Compressed Volume File) module
              cvf_module instead of auto-detection.  If  the  kernel  supports
              kmod,  the  cvf_format=xxx  option  also  controls on-demand CVF
              module loading.  This option is obsolete.

              Option passed to the CVF module.  This option is obsolete.

       debug  Turn on the  debug  flag.   A  version  string  and  a  list  of
              filesystem  parameters  will  be  printed  (these  data are also
              printed if the parameters appear to be inconsistent).

              If set, causes discard/TRIM commands to be issued to  the  block
              device  when  blocks  are freed.  This is useful for SSD devices
              and sparse/thinly-provisioned LUNs.

              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.

       nfs    If set, enables in-memory indexing of directory inodes to reduce
              the frequency of ESTALE errors in NFS client operations.  Useful
              only when the filesystem is exported via NFS.

       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.

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

              If set, the execute permission bits of the file will be  allowed
              only  if  the extension part of the name is .EXE, .COM, or .BAT.
              Not set by default.

              If set, ATTR_SYS attribute on FAT is handled as  IMMUTABLE  flag
              on Linux.  Not set by default.

       flush  If set, the filesystem will try to flush to disk more early than
              normal.  Not set by default.

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

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

Mount options for hfs

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

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

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

              Select  the  CDROM  session  to mount.  Defaults to leaving that
              decision to the  CDROM  driver.   This  option  will  fail  with
              anything but a CDROM as underlying device.

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

       quiet  Don't complain about invalid mount options.

Mount options for hpfs

       uid=value and gid=value
              Set the owner and group of all files. (Default: the uid and  gid
              of the current process.)

              Set  the  umask  (the  bitmask  of  the permissions that are not
              present).  The default is the umask of the current process.  The
              value is given in octal.

              Convert all files names to lower case, or leave them.  (Default:

              For conv=text,  delete  some  random  CRs  (in  particular,  all
              followed by NL) when reading a file.  For conv=auto, choose more
              or less  at  random  between  conv=binary  and  conv=text.   For
              conv=binary,  just  read  what  is  in  the  file.   This is the

              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
       filesystem (except that it is read-only, of course).

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

              Disable  the  use  of  Microsoft  Joliet  extensions,  even   if
              available.  Cf. map.

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

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

              For  non-Rock  Ridge volumes, normal name translation maps upper
              to lower case ASCII, drops a trailing `;1', and converts `;'  to
              `.'.   With  map=off  no  name translation is done.  See norock.
              (Default: map=normal.)  map=acorn is like  map=normal  but  also
              apply Acorn extensions if present.

              For  non-Rock  Ridge volumes, give all files the indicated mode.
              (Default: read and execute  permission  for  everybody.)   Since
              Linux 2.1.37 one no longer needs to specify the mode in decimal.
              (Octal is indicated by 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:

              (Default:  conv=binary.)   Since Linux 1.3.54 this option has no
              effect anymore.   (And  non-binary  settings  used  to  be  very
              dangerous, possibly leading to silent data corruption.)

       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. (Since 2.3.4.)

              Session begins from sector xxx. (Since 2.3.4.)

       The following options are the same as for vfat and specifying them only
       makes  sense  when  using  discs  encoded  using   Microsoft's   Joliet

              Character set to use for converting 16 bit Unicode characters on
              CD to 8 bit characters.  The default is iso8859-1.

       utf8   Convert 16 bit Unicode characters on CD to UTF-8.

Mount options for jfs

              Character set to use for converting from Unicode to ASCII.   The
              default  is  to  do  no conversion.  Use iocharset=utf8 for UTF8
              translations.  This requires CONFIG_NLS_UTF8 to be  set  in  the
              kernel .config file.

              Resize  the volume to value blocks.  JFS only supports growing a
              volume, not shrinking it.  This option is only  valid  during  a
              remount,  when  the  volume  is  mounted read-write.  The resize
              keyword with no value will grow the volume to the full  size  of
              the partition.

              Do  not write to the journal.  The primary use of this option is
              to allow for higher performance when  restoring  a  volume  from
              backup  media.  The integrity of the volume is not guaranteed if
              the system abnormally ends.

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

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

              These options are accepted but ignored.

Mount options for minix


Mount options for msdos

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

Mount options for ncpfs

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

Mount options for nfs and nfs4

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

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

Mount options for ntfs

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

              New name for the option earlier called iocharset.

       utf8   Use UTF-8 for converting file names.

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

              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 proc

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

Mount options for ramfs

       Ramfs is a memory based filesystem.  Mount it and you have it.  Unmount
       it and it is gone.  Present since Linux 2.3.99pre4.  There are no mount

Mount options for reiserfs

       Reiserfs is a journaling filesystem.

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

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

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

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

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

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

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

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

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

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

              Enable Extended User Attributes.  See the attr(5) manual page.

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

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

Mount options for romfs


Mount options for squashfs


Mount options for smbfs

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

Mount options for sysv


Mount options for tmpfs

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

              The same as size, but in blocks of PAGE_CACHE_SIZE

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

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

       mode=  Set initial permissions of the root directory.

       uid=   The user id.

       gid=   The group id.

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

                     prefers to allocate memory from the local node

                     prefers to allocate memory from the given Node

                     allocates memory only from nodes in NodeList

                     prefers to allocate from each node in turn

                     allocates from each node of NodeList in turn.

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

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

Mount options for ubifs

       UBIFS  is  a flash file system which works on top of UBI volumes.  Note
       that atime is not supported and is always turned off.

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

              ubiY   UBI device number 0, volume number Y

                     UBI device number X, volume with name NAME

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

       The following mount options are available:

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

              Do not bulk-read.  This is the default.

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

              Do not check data  CRC-32  checksums.   With  this  option,  the
              filesystem  does not check CRC-32 checksum for data, but it does
              check it for the internal  indexing  information.   This  option
              only  affects reading, not writing.  CRC-32 is always calculated
              when writing the data.

              Select the default compressor which is used when new  files  are
              written.   It  is  still  possible  to  read compressed files if
              mounted with the none option.

Mount options for udf

       udf is the "Universal Disk Format" filesystem defined  by  the  Optical
       Storage  Technology  Association,  and  is often used for DVD-ROM.  See
       also iso9660.

       gid=   Set the default group.

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

       uid=   Set the default user.

       unhide Show otherwise hidden files.

              Show deleted files in lists.

              Unset strict conformance.

              Set the NLS character set.

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

       novrs  Skip volume sequence recognition.

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

              Override standard anchor location.  Default: 256.

              Override the VolumeDesc location. (unused)

              Override the PartitionDesc location. (unused)

              Set the last block of the filesystem.

              Override the fileset block location. (unused)

              Override the root directory location. (unused)

Mount options for ufs

              UFS is a filesystem widely used in different operating  systems.
              The  problem are differences among implementations.  Features of
              some implementations are undocumented, so its hard to  recognize
              the type of ufs automatically.  That's why the user must specify
              the type of ufs by mount option.  Possible values are:

              old    Old format of  ufs,  this  is  the  default,  read  only.
                     (Don't forget to give the -r option.)

              44bsd  For  filesystems  created  by  a BSD-like system (NetBSD,
                     FreeBSD, OpenBSD).

              ufs2   Used in FreeBSD 5.x supported as read-write.

              5xbsd  Synonym for ufs2.

              sun    For filesystems created by SunOS or Solaris on Sparc.

              sunx86 For filesystems created by Solaris on x86.

              hp     For filesystems created by HP-UX, read-only.

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

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

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

              Set behavior on error:

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

                     These mount options don't do anything at present; when an
                     error is encountered only a console message is printed.

Mount options for umsdos

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

Mount options for vfat

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

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

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

              First  try  to make a short name without sequence number, before
              trying name~num.ext.

       utf8   UTF8 is the filesystem safe 8-bit encoding of  Unicode  that  is
              used  by the console.  It can be enabled for the filesystem with
              this option or disabled with utf8=0, utf8=no or utf8=false.   If
              `uni_xlate' gets set, UTF8 gets disabled.

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

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

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

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

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

Mount options for usbfs

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

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

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

Mount options for xenix


Mount options for xfs

              Sets the buffered I/O end-of-file preallocation size when  doing
              delayed  allocation  writeout.  Valid values for this option are
              page size (typically 4KiB) through to 1GiB, inclusive, in power-
              of-2 increments.

              The  default  behavior  is for dynamic end-of-file preallocation
              size,  which  uses  a  set  of  heuristics   to   optimise   the
              preallocation  size  based  on  the  current allocation patterns
              within the file and the access patterns to the file.  Specifying
              a fixed allocsize value turns off the dynamic behavior.

              The  options enable/disable an "opportunistic" improvement to be
              made in the way inline extended attributes are  stored  on-disk.
              When  the  new  form  is  used  for the first time when attr2 is
              selected (either when setting or removing  extended  attributes)
              the  on-disk  superblock  feature  bit  field will be updated to
              reflect this format being in use.

              The default behavior is determined by the  on-disk  feature  bit
              indicating  that  attr2  behavior  is  active.   If either mount
              option it set, then that becomes the new  default  used  by  the

              CRC enabled filesystems always use the attr2 format, and so will
              reject the noattr2 mount option if it is set.

              Enables/disables the use  of  block  layer  write  barriers  for
              writes into the journal and for data integrity operations.  This
              allows for drive level write caching to be enabled, for  devices
              that support write barriers.

              Enable/disable  the  issuing of commands to let the block device
              reclaim space freed by the filesystem.  This is useful  for  SSD
              devices, thinly provisioned LUNs and virtual machine images, but
              may have a performance impact.

              Note: It is  currently  recommended  that  you  use  the  fstrim
              application  to  discard  unused  blocks rather than the discard
              mount option because the performance impact of  this  option  is
              quite severe.

              These  options  define  what group ID a newly created file gets.
              When grpid is set, it takes the group ID  of  the  directory  in
              which it is created; otherwise it takes the fsgid of the current
              process, unless the directory has the setgid bit set,  in  which
              case  it  takes the gid from the parent directory, and also gets
              the setgid bit set if it is a directory itself.

              Make the data allocator  use  the  filestreams  allocation  mode
              across  the  entire  filesystem  rather than just on directories
              configured to use it.

              When ikeep  is  specified,  XFS  does  not  delete  empty  inode
              clusters  and  keeps  them  around  on  disk.   When  noikeep is
              specified, empty inode clusters are returned to the  free  space

              When  inode32  is  specified, it indicates that XFS limits inode
              creation to locations which will not  result  in  inode  numbers
              with more than 32 bits of significance.

              When  inode64  is specified, it indicates that XFS is allowed to
              create inodes at any location in the filesystem, including those
              which  will  result in inode numbers occupying more than 32 bits
              of significance.

              inode32 is  provided  for  backwards  compatibility  with  older
              systems  and  applications,  since  64  bits inode numbers might
              cause problems for some applications that  cannot  handle  large
              inode  numbers.   If applications are in use which do not handle
              inode numbers bigger than 32 bits, the inode32 option should  be

              If  "nolargeio"  is  specified,  the  optimal  I/O  reported  in
              st_blksize by stat(2) will be as small as possible to allow user
              applications  to  avoid inefficient read/modify/write I/O.  This
              is typically the page size  of  the  machine,  as  this  is  the
              granularity of the page cache.

              If  "largeio"  specified,  a  filesystem that was created with a
              "swidth" specified will return the "swidth" value (in bytes)  in
              st_blksize.    If  the  filesystem  does  not  have  a  "swidth"
              specified but does specify an "allocsize" then  "allocsize"  (in
              bytes)  will be returned instead.  Otherwise the behavior is the
              same as if "nolargeio" was specified.

              Set the number of in-memory log buffers.   Valid  numbers  range
              from 2–8 inclusive.

              The default value is 8 buffers.

              If  the  memory  cost  of  8  log  buffers  is too high on small
              systems, then it may be reduced at some cost to  performance  on
              metadata   intensive   workloads.   The  logbsize  option  below
              controls the size of each buffer and so is also relevant to this

              Set  the  size  of  each  in-memory log buffer.  The size may be
              specified in bytes, or in kibibytes (KiB)  with  a  "k"  suffix.
              Valid  sizes  for  version  1  and  version  2  logs  are  16384
              (value=16k) and 32768 (value=32k).  Valid sizes  for  version  2
              logs  also  include  65536  (value=64k), 131072 (value=128k) and
              262144 (value=256k).  The logbsize must be an  integer  multiple
              of the log stripe unit configured at mkfs time.

              The default value for version 1 logs is 32768, while the default
              value for version 2 logs is MAX(32768, log_sunit).

       logdev=device and rtdev=device
              Use an external log (metadata journal) and/or real-time  device.
              An  XFS  filesystem has up to three parts: a data section, a log
              section, and a real-time  section.   The  real-time  section  is
              optional,  and  the  log  section  can be separate from the data
              section or contained within it.

              Data allocations will not be aligned at stripe unit  boundaries.
              This  is only relevant to filesystems created with non-zero data
              alignment parameters (sunit, swidth) by mkfs.

              The filesystem will be mounted without running log recovery.  If
              the  filesystem  was  not  cleanly unmounted, it is likely to be
              inconsistent when mounted in "norecovery" mode.  Some  files  or
              directories  may not be accessible because of this.  Filesystems
              mounted "norecovery" must be mounted read-only or the mount will

       nouuid Don't  check  for  double  mounted  file  systems using the file
              system uuid.  This is useful to mount LVM snapshot volumes,  and
              often  used  in combination with "norecovery" for mounting read-
              only snapshots.

              Forcibly turns off all quota accounting and  enforcement  within
              the filesystem.

              User  disk  quota  accounting  enabled,  and limits (optionally)
              enforced.  Refer to xfs_quota(8) for further details.

              Group disk quota  accounting  enabled  and  limits  (optionally)
              enforced.  Refer to xfs_quota(8) for further details.

              Project  disk  quota  accounting enabled and limits (optionally)
              enforced.  Refer to xfs_quota(8) for further details.

       sunit=value and swidth=value
              Used to specify the stripe unit and width for a RAID device or a
              stripe  volume.   "value"  must  be  specified in 512-byte block
              units.  These options are only relevant to filesystems that were
              created with non-zero data alignment parameters.

              The  sunit  and  swidth  parameters specified must be compatible
              with the  existing  filesystem  alignment  characteristics.   In
              general,  that  means  the  only  valid  changes  to  sunit  are
              increasing it by a power-of-2 multiple.  Valid swidth values are
              any integer multiple of a valid sunit value.

              Typically  the  only  time  these mount options are necessary if
              after an underlying RAID device has had it's geometry  modified,
              such as adding a new disk to a RAID5 lun and reshaping it.

              Data  allocations  will be rounded up to stripe width boundaries
              when the current end of file is being extended and the file size
              is larger than the stripe width size.

       wsync  When specified, all filesystem namespace operations are executed
              synchronously.  This ensures that when the  namespace  operation
              (create,  unlink, etc) completes, the change to the namespace is
              on stable storage.  This is useful in HA setups  where  failover
              must   not  result  in  clients  seeing  inconsistent  namespace
              presentation during or after a failover event.


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

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

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

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

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

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

              mount /tmp/disk.img /mnt

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

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

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

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


       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]   [-o   options]   [-t

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

       The   command  mount  does  not  pass  the  mount  options  unbindable,
       runbindable, private, rprivate, slave, rslave, shared,  rshared,  auto,
       noauto,  comment, x-*, loop, offset and sizelimit to the mount.<suffix>
       helpers.  All other options are  used  in  a  comma-separated  list  as
       argument to the -o option.


       /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


              overrides the default location of the fstab file

              overrides the default location of the mtab file

              enables debug output


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


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

       Some  Linux filesystems don't support -o sync and -o dirsync (the ext2,
       ext3, 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  files /etc/mtab and /proc/mounts don't match on
       systems with 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.  remote  NFS  server.   In
       particular  case  the  mount command may reports unreliable information
       about a NFS mount point and the /proc/mounts file usually contains more
       reliable information.) This is another reason to replace mtab file with
       symlink to the /proc/mounts file.

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

       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

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