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MOUNT(8)                     System Administration                    MOUNT(8)

       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  sev-
       eral  devices.  The mount command serves to attach the filesystem found
       on some device to the big file tree.  Conversely, the umount(8) command
       will detach it again.

       The 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),  espe-
              cially  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 spe-
              cial  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

              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 por-
              table.  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 simul-

              When mounting a filesystem mentioned in fstab or mtab,  it  suf-
              fices  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 spec-
              ified.  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  exam-

                     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  to
              see the current propagation flags.

       The shared subtree operations.
              Since  Linux  2.6.15 it is possible to mark a mount and its sub-
              mounts 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 mas-
              ter, 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  pre-
              ceeding  mount  operations  were successful.  Note that this use
              case is not atomic.  It is possible to specify  the  propagation
              flags  in  fstab(5)  as  mount  options (private, slave, shared,
              unbindable, rprivate, rslave, rshared, runbindable).

              For example:

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

              is the same as:

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

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

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

       Command-line options available for the mount command are:

       -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 deter-
              mine what the mount command is trying to do.   It  can  also  be
              used  to  add entries for devices that were mounted earlier with
              the -n option.  The -f option checks for an existing  record  in
              /etc/mtab and fails when the record already exists (with a regu-
              lar non-fake mount, this check is done by the kernel).

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

       -l, --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 reis-
              erfs using reiserfstune(8).

       -n, --no-mtab
              Mount without writing in /etc/mtab.  This is necessary for exam-
              ple 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 com-
              mand-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 exam-
              ple, ext3 and ext4 will replay the journal if the filesystem  is
              dirty.   To  prevent  this kind of write access, you may want to
              mount an ext3  or  ext4  filesystem  with  the  ro,noload  mount
              options  or  set  the block device itself to read-only mode, see
              the blockdev(8) command.

       -w, --rw, --read-write
              Mount the filesystem read/write.  This is the default.   A  syn-
              onym 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,  hfs-
              plus,  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 usbde-
              vfs.  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  filesys-
              tem  type is required.  For a few types however (like nfs, nfs4,
              cifs, smbfs, ncpfs) an ad hoc code is necessary.  The nfs, nfs4,
              cifs,  smbfs,  and  ncpfs filesystems have a separate mount pro-
              gram.  In order to make it possible to treat all types in a uni-
              form  way,  mount  will execute the program /sbin/mount.type (if
              that exists) when called with type type.  Since  different  ver-
              sions  of  the  smbmount  program have different calling conven-
              tions, /sbin/mount.smbfs may have to be a shell script that sets
              up the desired call.

              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  _net-
              dev specified in the options field in the /etc/fstab file.

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

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

                     mount -a -t ext2 -O _netdev

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

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

                     mount LABEL=mydisk -o noatime,nodev,nosuid

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

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

              A commonly used option  for  removable  media  is  context="sys-

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

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

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

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

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

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

       exec   Permit execution of binaries.

       noexec Do not permit direct execution of any binaries  on  the  mounted
              filesystem.   (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 ear-
              lier  than the current modify or change time.  (Similar to noat-
              ime, 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 modi-

              Since Linux 2.6.30, the kernel defaults to the behavior provided
              by  this option (unless noatime was specified), and the stricta-
              time 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 com-
              monly used to change the mount flags  for  a  filesystem,  espe-
              cially  to  make  a  readonly  filesystem writable.  It does not
              change device or mount point.

              The remount 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  subse-
              quent options, as in the option line user,exec,dev,suid).

       nouser Forbid  an  ordinary (i.e., non-root) user to mount the filesys-
              tem.  This is the default; it does not imply any other options.

       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-<app-
              name>.<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  Documenta-

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

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

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

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

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

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

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

              Print an informational message for each successful mount.

              Prefix used before volume name, when following a link.

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

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

              Give explicitly the location of the root block.

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

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

Mount options for 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 nodata-
              sum 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 sig-
              nificant performance impact.  (The fstrim command is also avail-
              able 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 previ-
              ously 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  sector-
              size, 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 some-
              thing 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 subvol-
              ume list" to see subvolume ID numbers.

       subvolrootid=objectid  (deprecated)
              Mount subvolume specified by objectid rather than the root  sub-
              volume.  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 pack-
       age 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  CON-
              FIG_DEVPTS_MULTIPLE_INSTANCES  is enabled in the kernel configu-

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


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

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

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

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

Mount options for 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 behav-
              ior 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 ker-
              nel 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  con-
              tinue,  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 sup-
              port.  You need the quota utilities to actually enable and  man-
              age 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 avail-
              able 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

       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.  Other-
              wise, it specifies the number of the inode which will  represent
              the ext3 filesystem's journal file; ext3 will create a new jour-
              nal, 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 filesys-
              tem, pass the mode to the kernel as boot parameter,  e.g.  root-

                     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 cor-
              ruption 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 descrip-
              tor 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  filesys-
              tem  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  auto-
              matically  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 us (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  pur-
              poses.   This  is  normally  used  while remounting a filesystem
              which is already mounted.

              Many broken applications don't use fsync() when replacing exist-
              ing 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  mil-
              liseconds  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 rou-
              tines  to  quickly  locate  extents  which  might  overlap  with
              filesystem  metadata blocks.  This option is intended for debug-
              ging 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 jour-
              naling  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  environ-
              ments, 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  spe-
                     cial  characters that are sometimes used on Linux but are
                     not accepted by MS-DOS (+, =, etc.) are rejected.

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

              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  con-
              version.   Several  people  have  had  their data ruined by this
              translation.  Beware!

              For filesystems mounted in binary mode, a conversion tool (from-
              dos/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 mod-
              ule loading.  This option is obsolete.

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

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

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

              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  any-
              thing but a CDROM as underlying device.

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

       quiet  Don't complain about invalid mount options.

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

              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  fol-
              lowed 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 filesys-
       tem (except that it is read-only, of course).

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

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

              With  check=relaxed, a filename is first converted to lower case
              before doing the  lookup.   This  is  probably  only  meaningful
              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  dan-
              gerous, 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  exten-

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

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

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

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

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

              Default.  Commit metadata changes  to  the  journal.   Use  this
              option to remount a volume where the nointegrity option was pre-
              viously 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 con-
              tinue, 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 incon-
       sistency, it reports an error and sets the file system read-only.   The
       filesystem can be made writable again by remounting it.

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

Mount options for 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 pre-
                     serves locality,  mapping  lexicographically  close  file
                     names  to  close  hash values.  This option should not be
                     used, as it causes a high probability of hash collisions.

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

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

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

              Tunes  the  block  allocator.   This  may  provide   performance
              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 sit-

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

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

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

       barrier=none / barrier=flush
              This disables / enables the use of write barriers in  the  jour-
              naling   code.   barrier=none  disables,  barrier=flush  enables
              (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 con-
       structed 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 sys-
              tem  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 advis-
              able to omit the mpol option from automatic mount  options.   It
              can  be added later, when the tmpfs is already mounted on Mount-
              Point, by 'mount -o remount,mpol=Policy:NodeList MountPoint'.

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 char-
              acter, is: ':', (u & 0x3f), ((u>>6) & 0x3f), (u>>12).

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

              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 prealloca-
              tion 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 appli-
              cation to discard unused blocks rather than  the  discard  mount
              option  because  the  performance impact of this option is quite

              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 clus-
              ters and keeps them around on disk.  When noikeep is  specified,
              empty inode clusters are returned to the free space pool.

              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  sys-
              tems  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 speci-

              If "nolargeio" is specified, the optimal I/O reported in st_blk-
              size 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 granu-
              larity 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" speci-
              fied 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 sys-
              tems, then it may be reduced at  some  cost  to  performance  on
              metadata  intensive  workloads.   The logbsize option below con-
              trols 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 sec-
              tion 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 sys-
              tem 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 gen-
              eral,  that means the only valid changes to sunit are increasing
              it by a power-of-2 multiple.  Valid swidth values are any  inte-
              ger 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 presen-
              tation 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, mean-
       ing  that  any  loop  device allocated by mount will be freed by umount
       independently of /etc/mtab.

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

       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 type.sub-

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

       /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 particu-
       lar  case  the mount command may reports unreliable information about a
       NFS mount point and the /proc/mounts file usually contains  more  reli-
       able  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

util-linux                         July 2014                          MOUNT(8)

Czas wygenerowania: 0.00032 sek.

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