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

       The standard form of the mount command is:

              mount -t type device dir

       This tells the kernel to attach the filesystem found on device (which is of type type)  at
       the directory dir.  The previous contents (if any) and owner and mode of dir become invis‐
       ible, 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 interpre‐
       tation of the given argument.  For example:

              mount --target /mountpoint

       The listing.
              The listing mode is maintained for backward compatibility only.

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

              The following command lists all mounted filesystems (of type 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 knuth.cwi.nl:/dir.  It is also possible to  indicate  a
              block  special device using its filesystem label or UUID (see the -L and -U options
              below), or its partition label or UUID.  (Partition identifiers are  supported  for
              example for GUID Partition Tables (GPT).)

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

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

              Note  that mount(8) uses UUIDs as strings.  The UUIDs from the command line or from
              fstab(5) are not converted to internal binary representation.  The string represen‐
              tation 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 details).

              The command

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

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

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

              The  programs  mount  and umount traditionally maintained list of currently mounted
              filesystems in the file /etc/mtab.  The mtab file is still supported, but it's rec‐
              ommended  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

                     mount device|dir -o options

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

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

                     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 com‐

                     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 sub‐
              mounts.  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 origi‐
              nal 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 example:

                     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 example:

                     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 mountpoint.

              Note also that moving a mount residing under a shared mount is invalid  and  unsup‐
              ported.  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 submounts as shared, pri‐
              vate, slave or unbindable.  A shared mount provides the ability to  create  mirrors
              of  that mount such that mounts and unmounts within any of the mirrors propagate to
              the other mirror.  A slave mount receives propagation from its master, but not vice
              versa.  A private mount carries no propagation abilities.  An unbindable mount is a
              private mount which cannot be cloned through a bind operation.  The detailed seman‐
              tics are documented in Documentation/filesystems/sharedsubtree.txt file in the ker‐
              nel 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 neces‐
              sary 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 EXPERIMEN‐
              TAL.   The  propagation  flags are applied by additional mount(2) syscalls when the
              preceeding mount operations were successful.   Note  that  this  use  case  is  not
              atomic.   It  is  possible  to  specify  the propagation flags in fstab(5) as mount
              options (private, slave, shared, unbindable, rprivate,  rslave,  rshared,  runbind‐

              For example:

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

              is the same as:

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

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

       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 sec‐

       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 paral‐
              lel.   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  obvi‐
              ous,  this ``fakes'' mounting the filesystem.  This option is useful in conjunction
              with the -v flag to determine what the mount command is trying to do.  It can  also
              be  used  to  add entries for devices that were mounted earlier with the -n option.
              The -f option checks for an existing record in /etc/mtab and fails when the  record
              already exists (with a regular non-fake mount, this check is done by the kernel).

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              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 filesys‐
              tem 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 exam‐
              ple, the command

                     mount -a -t nomsdos,ext

              mounts all filesystems except those of type msdos and ext.

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

                     mount -a -O no_netdev

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

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

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

                     mount -a -t ext2 -O _netdev

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

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

                     mount LABEL=mydisk -o noatime,nodev,nosuid

              For more details, see the FILESYSTEM-INDEPENDENT MOUNT OPTIONS and  FILESYSTEM-SPE‐
              CIFIC 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 filesystems).

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

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

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

              Do not update inode access times on this filesystem (e.g., for faster access on the
              news spool to speed up news servers).

       auto   Can be mounted with the -a option.

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

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

              A  commonly  used  option  for removable media is context="system_u:object_r:remov‐

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

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

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

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

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

              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 quot‐
              ing 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 async.

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

       dev    Interpret character or block special devices on the filesystem.

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

              Update directory inode access times on this filesystem.  This is the default.

              Do not update directory inode access times on this filesystem.

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

       exec   Permit execution of binaries.

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

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

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

              Do not increment the i_version inode field.

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

       nomand Do not allow mandatory locks on this filesystem.

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

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

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

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

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

              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 effect.

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

       silent Turn on the silent flag.

       loud   Turn off the silent flag.

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

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

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

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

              After  this  call all old mount options are replaced and arbitrary stuff from fstab
              is ignored, except the loop= option which is internally generated and maintained by
              the mount command.

              mount -o remount,rw  /dir

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

       ro     Mount the filesystem read-only.

       rw     Mount the filesystem read-write.

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

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

       nouser Forbid an ordinary (i.e., non-root) user to mount  the  filesystem.   This  is  the
              default; it does not imply any other 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 users,exec,dev,suid).

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

              Allow to make a target directory (mountpoint).  The optional argument  mode  speci‐
              fies  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 Documentation/filesystems.

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

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

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

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

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

              Do not allow any changes to the protection bits on the filesystem.

       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 device.

              Give explicitly the location of the root block.

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

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

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

              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 required).

              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 info.

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

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

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

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

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

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

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

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

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

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

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

       noacl  Enable/disable support for Posix Access Control Lists (ACLs).  See the acl(5)  man‐
              ual 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

              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 dat‐

              Enable/disable the tree logging used for fsync and O_SYNC writes.

              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  read‐

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

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

              Disable freespace cache loading without clearing the cache.

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

              Options  to  control ssd allocation schemes.  By default, BTRFS will enable or dis‐
              able 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 well.

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

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

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

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

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

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

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 options:

       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

              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 imple‐
              mented  in  linux kernel versions starting with 2.6.29.  Further, this mount option
              is valid only if CONFIG_DEVPTS_MULTIPLE_INSTANCES is enabled in the kernel 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 filesystem.

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

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

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

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 source.

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

              Support POSIX Access Control Lists (or not).

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

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

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

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

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

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

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

       debug  Print debugging info upon each (re)mount.

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

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

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

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

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

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

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

              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 jour‐
       naling.  It supports the same options as ext2 as well as the following additions:

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

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

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

              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  incon‐
              sistencies that can lead to any number of problems.

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

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

                     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 filesys‐
                     tem 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

              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  dis‐
              ables,  barrier=1 enables (default).  This also requires an IO stack which can sup‐
              port barriers, and if jbd gets an error on a barrier write, it will disable  barri‐
              ers  again with a warning.  Write barriers enforce proper on-disk ordering of jour‐
              nal commits, making volatile disk write caches safe to  use,  at  some  performance
              penalty.   If your disks are battery-backed in one way or another, disabling barri‐
              ers may safely improve performance.

              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
              grpjquota=aquota.group 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  scala‐
       bility and reliability enhancements for supporting large filesystem.

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

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

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

              Deferring block allocation until write-out time.

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

              Maximum amount of time ext4 should wait for additional filesystem operations to  be
              batch together with a synchronous write operation.  Since a synchronous write oper‐
              ation 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  algo‐
              rithm  used is designed to automatically tune for the speed of the disk, by measur‐
              ing the amount of time (on average) that it takes to finish committing  a  transac‐
              tion.  Call this time the "commit time".  If the time that the transaction has been
              running is less than the commit time, ext4 will try sleeping for the commit time to
              see  if  other  operations will join the transaction.  The commit time is capped by
              the max_batch_time, which defaults to 15000 µs (15 ms).  This optimization  can  be
              turned off entirely by setting max_batch_time to 0.

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

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

       abort  Simulate the effects of calling ext4_abort() for debugging purposes.  This is  nor‐
              mally used while remounting a filesystem which is already mounted.

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

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

              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 commit‐
              ted.  This provides roughly the same level of guarantees as ext3,  and  avoids  the
              "zero-length"  problem  that  can  happen  when a system crashes before the delayed
              allocation blocks are forced to disk.

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

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

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

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

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

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

              This  limits  the size of the directories so that any attempt to expand them beyond
              the specified limit in kilobytes will cause an ENOSPC error.   This  is  useful  in
              memory-constrained environments, where a very large directory can cause severe per‐
              formance 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 sys‐
              tem's style.)

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

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

              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

              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  cur‐
              rent 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  trun‐
                     cated  (e.g. verylongname.foobar becomes verylong.foo), leading and embedded
                     spaces are accepted in each name part (name and extension).

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

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

              Sets  the  codepage for converting to shortname characters on FAT and VFAT filesys‐
              tems.  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, dvi).

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

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

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

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

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

              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 Uni‐
              code 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  exten‐
              sion 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

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

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

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

       quiet  Don't complain about invalid mount options.

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

              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: case=lower.)

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

              Do not abort mounting when certain consistency checks fail.

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

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

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

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

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

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

       uid=value and gid=value
              Give all files in the filesystem the indicated user or group id, possibly  overrid‐
              ing 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 spec‐
              ify 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 inacces‐

              Set the block size to the indicated value.  (Default: block=1024.)

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

       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 extensions.

              Character  set to use for converting 16 bit Unicode characters on CD to 8 bit char‐
              acters.  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  CON‐
              FIG_NLS_UTF8 to be set in the kernel .config file.

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

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

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

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

              These options are accepted but ignored.

Mount options for minix

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

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

Mount options for nfs and nfs4
       See the options section of the nfs(5) man page (nfs-utils package must be installed).

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

Mount options for ntfs
              Character set to use when returning file names.  Unlike VFAT, NTFS suppresses names
              that contain nonconvertible characters.  Deprecated.

              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 charac‐
              ters.   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 bigen‐
              dian encoding.

              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 see.

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 options.

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  com‐
              patible with reiserfs 3.5 tools.

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

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

              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 EHASH‐
                     COLLISION 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

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

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

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

              Disable the border allocator algorithm invented by Yury Yu. Rupasov.  This may pro‐
              vide performance improvements in some situations.

       nolog  Disable journaling.  This will provide slight performance improvements in some sit‐
              uations 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

       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 pack‐
              ing of files into the tree.

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

              A remount option which permits online expansion of reiserfs partitions.   Instructs
              reiserfs  to assume that the device has number blocks.  This option is designed for
              use with devices which are under logical volume management (LVM).  There is a  spe‐
              cial  resizer utility which can be obtained from ftp://ftp.namesys.com/pub/reiserf‐

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

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

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

Mount options for romfs

Mount options for squashfs

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

Mount options for sysv

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

              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 lower.

       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 ker‐
              nel  does not support NUMA; and will fail if its nodelist specifies a node which is
              not online.  If your system relies on that tmpfs being mounted, but  from  time  to
              time  runs a kernel built without NUMA capability (perhaps a safe recovery kernel),
              or with fewer nodes online, then it is advisable to omit the mpol option from auto‐
              matic  mount  options.  It can be added later, when the tmpfs is already mounted on
              MountPoint, 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 sys‐
              tem.  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, One‐
              NAND 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 cal‐
              culated 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  undocu‐
              mented,  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 X.

              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  encoun‐
                     tered only a console message is printed.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Mount options for xenix

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

              The default behavior is for dynamic end-of-file preallocation size,  which  uses  a
              set  of  heuristics to optimise the preallocation size based on the current alloca‐
              tion 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 filesystem.

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

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

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

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

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

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

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

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

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

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

              The default value is 8 buffers.

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

              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 logb‐
              size must be an integer multiple of the log stripe unit configured at mkfs time.

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

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

              Data allocations will not be aligned at stripe unit boundaries.  This is only rele‐
              vant 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.   Filesys‐
              tems mounted "norecovery" must be mounted read-only or the mount will fail.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              mount /tmp/disk.img /mnt

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

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

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

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

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

       0      success

       1      incorrect invocation or permissions

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

       4      internal mount bug

       8      user interrupt

       16     problems writing or locking /etc/mtab

       32     mount failure

       64     some mount succeeded

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

       The syntax of external mount helpers is:

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

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

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

       /etc/fstab        filesystem table

       /etc/mtab         table of mounted filesystems

       /etc/mtab~        lock file

       /etc/mtab.tmp     temporary file

       /etc/filesystems  a list of filesystem types to try

              overrides the default location of the fstab file

              overrides the default location of the mtab file

              enables debug output

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

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

       Some  Linux filesystems don't support -o sync and -o dirsync (the ext2, ext3, fat and vfat
       filesystems do support synchronous updates (a la BSD) when mounted with the sync option).

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

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

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

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

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

       Karel Zak <kzak AT redhat.com>

       The mount command is part of the util-linux package and is available  from  ftp://ftp.ker‐

util-linux                                  July 2014                                    MOUNT(8)

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