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           mount [-lhV]
           mount -a [-fFnrsvw] [-t vfstype] [-O optlist]
           mount [-fnrsvw] [-o option[,option]...]  device|dir
           mount [-fnrsvw] [-t vfstype] [-o options] device dir


           All files accessible in a Unix system are arranged in one big tree, the
           file hierarchy, rooted at /.  These files can be spread out  over  sev-
           eral  devices.  The mount command serves to attach the filesystem found
           on some device to the big file tree. Conversely, the umount(8)  command
           will detach it again.
           The standard form of the mount command, is
                  mount -t type device dir
           This  tells  the kernel to attach the filesystem found on device (which
           is of type type) at the directory dir.  The previous contents (if  any)
           and  owner  and  mode  of  dir  become  invisible,  and as long as this
           filesystem remains mounted, the pathname dir refers to the root of  the
           filesystem on device.
           The listing and help.
                  Three forms of invocation do not actually mount anything:
                  mount -h
                         prints a help message
                  mount -V
                         prints a version string
                  mount [-l] [-t type]
                         lists all mounted filesystems (of type type).  The option
                         -l adds the labels in this listing.  See below.
           The device indication.
                  Most devices are indicated by a file name (of  a  block  special
                  device),  like /dev/sda1, but there are other possibilities. For
                  example, in the case of an  NFS  mount,  device  may  look  like
           It  is possible to indicate a block special
                  device using its volume LABEL or UUID (see the -L and -U options
                  The  recommended  setup  is  to use LABEL=<label> or UUID=<uuid>
                  tags rather than /dev/disk/by-{label,uuid} udev symlinks in  the
                  /etc/fstab   file.  The  tags  are  more  readable,  robust  and
                  portable. The mount(8) command internally uses udev symlinks, so
                  use   the   symlinks   in   /etc/fstab  is  not  advantage  over
                         mount -a [-t type] [-O optlist]
                  (usually given in a bootscript) causes all filesystems mentioned
                  in fstab (of the proper type and/or having  or  not  having  the
                  proper  options)  to  be  mounted as indicated, except for those
                  whose line contains the noauto keyword.  Adding  the  -F  option
                  will make mount fork, so that the filesystems are mounted simul-
                  When mounting a filesystem mentioned in fstab or mtab,  it  suf-
                  fices to give only the device, or only the mount point.
                  The  programs  mount  and  umount  maintain  a list of currently
                  mounted filesystems in the file /etc/mtab.  If no arguments  are
                  given to mount, this list is printed.
                  The  mount  program  does not read the /etc/fstab file if device
                  (or LABEL/UUID) and dir are specified. For example:
                         mount /dev/foo /dir
                  If you want to override mount options from /etc/fstab  you  have
                  to use:
                         mount device|dir -o <options>
                  and then the mount options from command line will be appended to
                  the list of options from /etc/fstab.   The  usual  behaviour  is
                  that the last option wins if there is more duplicated options.
                  When  the  proc  filesystem is mounted (say at /proc), the files
                  /etc/mtab and /proc/mounts have very similar contents. The  for-
                  mer  has  somewhat  more  information, such as the mount options
                  used, but is not  necessarily  up-to-date  (cf.  the  -n  option
                  below).  It  is possible to replace /etc/mtab by a symbolic link
                  to /proc/mounts, and especially when you have very large numbers
                  of mounts things will be much faster with that symlink, but some
                  information is lost that way, and in particular using the "user"
                  option will fail.
           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 system.
                  Thus, given a line
                         /dev/cdrom  /cd  iso9660  ro,user,noauto,unhide
                  any  user  can  mount  the iso9660 filesystem found on his CDROM
                  using the command
                  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 shortoption
                         mount -B olddir newdir
                  or fstab entry is:
                         /olddir /newdir none bind
                  After  this  call the same contents is accessible in two places.
                  One can also remount a single file (on a single file).
                  This call attaches only (part of) a single filesystem, not  pos-
                  sible  submounts.  The entire file hierarchy including submounts
                  is attached a second place using
                         mount --rbind olddir newdir
                  or shortoption
                         mount -R olddir newdir
                  Note that the filesystem mount options will remain the  same  as
                  those  on  the  original  mount  point, and cannot be changed by
                  passing the -o  option  along  with  --bind/--rbind.  The  mount
                  options  can be changed by a separate remount command, for exam-
                         mount --bind olddir newdir
                         mount -o remount,ro newdir
           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
                  or shortoption
                         mount -M olddir newdir
                  This  will  cause  the  contents which previously appeared under
                  olddir to be accessed under newdir.  The  physical  location  of
                  the files is not changed.
                  Note  also  that moving a mount residing under a shared mount is
                  invalid and unsupported (in the other words the  parent  of  the
                  olddir    has   to   use   private   propagation   flag).    See
                  /proc/self/mountinfo for the current propagation flags.
           The shared subtrees operations.
                  Since Linux 2.6.15 it is possible to mark a mount and  its  sub-
                  mounts  as  shared, private, slave or unbindable. A shared mount
                  provides ability to create  mirrors  of  that  mount  such  that
                  of all the mounts under a given mountpoint.
                         mount --make-rshared mountpoint
                         mount --make-rslave mountpoint
                         mount --make-rprivate mountpoint
                         mount --make-runbindable mountpoint


           The full set of mount options used by an invocation of mount is  deter-
           mined by first extracting the mount options for the filesystem from the
           fstab table, then applying any options specified by  the  -o  argument,
           and finally applying a -r or -w option, when present.
           Command line options available for the mount command:
           -V, --version
                  Output version.
           -h, --help
                  Print a help message.
           -v, --verbose
                  Verbose mode.
           -a, --all
                  Mount all filesystems (of the given types) mentioned in fstab.
           -F, --fork
                  (Used  in  conjunction  with -a.)  Fork off a new incarnation of
                  mount for each device.  This will do  the  mounts  on  different
                  devices  or  different  NFS  servers  in parallel.  This has the
                  advantage that it is faster; also NFS timeouts go in parallel. A
                  disadvantage  is  that  the  mounts are done in undefined order.
                  Thus, you cannot use this option if you want to mount both  /usr
                  and /usr/spool.
           -f, --fake
                  Causes  everything to be done except for the actual system call;
                  if it's not obvious, this  ''fakes''  mounting  the  filesystem.
                  This  option is useful in conjunction with the -v flag to deter-
                  mine what the mount command is trying to do. It can also be used
                  to add entries for devices that were mounted earlier with the -n
                  option. The -f option checks for existing  record  in  /etc/mtab
                  and  fails when the record already exists (with regular non-fake
                  mount, this check is done by kernel).
           -i, --internal-only
                  Don't  call  the  /sbin/mount.<filesystem>  helper  even  if  it
           -l     Add  the  labels in the mount output. Mount must have permission
           -p, --pass-fd num
                  In  case  of  a  loop mount with encryption, read the passphrase
                  from file descriptor num instead of from the terminal.
           -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. This option exists for  support
                  of the Linux autofs-based automounter.
           -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 or ext4 will replay its journal if the filesystem is dirty.
                  To prevent this kind of write access, you may want to mount ext3
                  or  ext4  filesystem  with  "ro,noload" mount options or set the
                  block device to read-only mode, see command blockdev(8).
           -w, --rw
                  Mount the filesystem read/write. This is the default. A  synonym
                  is -o rw.
           -L label
                  Mount the partition that has the specified label.
           -U 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, --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,  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  ker-
                  The  programs mount and umount support filesystem subtypes.  The
                  subtype  is  defined  by   '.subtype'   suffix.    For   example
                  'fuse.sshfs'.  It's  recommended  to use subtype notation rather
                  than  add  any  prefix  to  the  mount   source   (for   example
                  '' is depreacated).
                  mount will try to guess the desired type.  Mount uses the  blkid
                  or  volume_id  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 * only, mount will read /proc/filesystems afterwards.
                  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.  Warning:  the  probing  uses  a
                  heuristic  (the presence of appropriate 'magic'), and could rec-
                  ognize the wrong filesystem  type,  possibly  with  catastrophic
                  consequences.  If  your  data  is  valuable,  don't ask mount to
                  More than one type may be specified in a comma  separated  list.
                  The  list of filesystem types can be prefixed with no to specify
                  the filesystem types on which no action should be taken.   (This
                  can be meaningful with the -a option.) For example, the command:
                         mount -a -t nomsdos,ext
                  mounts all filesystems except those of type msdos and ext.
           -O, --test-opts opts
                  Used in conjunction with -a, to limit the set of filesystems  to
                  which  the -a is applied.  Like -t in this regard except that it
                  is useless except in the context of -a.  For example,  the  com-
                         mount -a -O no_netdev
                  mounts  all filesystems except those which have the option _net-
                  dev specified in the options field in the /etc/fstab file.
                  It is different from -t in that each option is matched  exactly;
                  a  leading no at the beginning of one option does not negate the
                  The -t and -O options are cumulative in  effect;  that  is,  the
                         mount -a -t ext2 -O _netdev
                  mounts  all  ext2  filesystems  with the _netdev option, not all
                  filesystems that are either ext2  or  have  the  _netdev  option
           -o, --options opts
                  Remount a subtree and all possible submounts somewhere else  (so
                  that its contents are available in both places). See above.
           -M, --move
                  Move a subtree to some other place. See above.


           Some  of  these  options  are  only  useful  when  they  appear  in the
           /etc/fstab file.
           Some of these options could be enabled or disabled by  default  in  the
           system  kernel.  To  check  the  current  setting  see  the  options in
           /proc/mounts. Note that filesystems also have  per-filesystem  specific
           default  mount  options  (see  for  example  tune2fs -l output for extN
           The following options apply to any filesystem  that  is  being  mounted
           (but  not every filesystem actually honors them - e.g., the sync option
           today has effect only for ext2, ext3, fat, vfat and ufs):
           async  All I/O to the filesystem should be  done  asynchronously.  (See
                  also the sync option.)
           atime  Do  not  use noatime feature, then the inode access time is con-
                  trolled by kernel defaults. See also the description for  stric-
                  tatime and relatime mount options.
                  Do  not  update  inode access times on this filesystem (e.g, for
                  faster access on the news spool to speed up news servers).
           auto   Can be mounted with the -a option.
           noauto Can only be mounted explicitly (i.e., the  -a  option  will  not
                  cause the filesystem to be mounted).
           context=context,  fscontext=context,  defcontext=context  and  rootcon-
                  The  context= option is useful when mounting filesystems that do
                  not support extended attributes, such as a floppy or  hard  disk
                  formatted  with  VFAT,  or systems that are not normally running
                  under SELinux, such as an ext3 formatted disk from a non-SELinux
                  workstation. You can also use context= on filesystems you do not
                  trust, such as a floppy. It also  helps  in  compatibility  with
                  xattr-supporting filesystems on earlier 2.4.<x> kernel versions.
                  Even where xattrs are supported, you can save time not having to
                  label  every file by assigning the entire disk one security con-
                  A commonly used  option  for  removable  media  is  context=sys-
                  selves.  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 unla-
                  beled  files  in  the policy and requires a filesystem that sup-
                  ports xattr labeling.
                  The rootcontext= option allows you to explicitly label the  root
                  inode of a FS being mounted before that FS or inode because vis-
                  able to userspace. This was found to be useful for  things  like
                  stateless linux.
                  For more details, see selinux(8)
                  Use  default  options: rw, suid, dev, exec, auto, nouser, async,
                  and relatime.
                  Note that the real set of the all default mount options  depends
                  on kernel and filesystem type. See the begin of this section for
                  more details.
           dev    Interpret character or block special devices on the  filesystem.
           nodev  Do  not interpret character or block special devices on the file
                  Update directory inode access times on this filesystem. This  is
                  the default.
                  Do not update directory inode access times on this filesystem.
                  All  directory updates within the filesystem should be done syn-
                  chronously.  This affects the  following  system  calls:  creat,
                  link, unlink, symlink, mkdir, rmdir, mknod and rename.
           exec   Permit execution of binaries.
           noexec Do  not  allow  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
                  The filesystem resides on a device that requires network  access
                  (used  to  prevent  the  system  from  attempting to mount these
                  filesystems until the network has been enabled on the system).
           nofail Do not report errors for this device if it does not exist.
                  Update inode access times relative to  modify  or  change  time.
                  Access time is only updated if the previous access time was ear-
                  lier than the current modify or change time. (Similar  to  noat-
                  ime,  but  doesn't break mutt or other applications that need to
                  know if a file has been read since the last time  it  was  modi-
                  Since Linux 2.6.30, the kernel defaults to the behavior provided
                  by this option (unless noatime was  specified), and the stricta-
                  time  option  is  required  to  obtain traditional semantics. In
                  addition, since Linux 2.6.30, the file's  last  access  time  is
                  always  updated  if  it  is more than 1 day old.
                  Do  not  use  relatime  feature.  See also the strictatime mount
                  Allows to explicitly requesting full atime updates.  This  makes
                  it  possible  for  kernel to defaults 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  behaviour  for  inode  access  time
           suid   Allow set-user-identifier or set-group-identifier bits  to  take
           nosuid Do not allow set-user-identifier or set-group-identifier bits to
                  take effect. (This seems safe, but is in fact rather  unsafe  if
                  you have suidperl(1) installed.)
           owner  Allow  an ordinary (i.e., non-root) user to mount the filesystem
                  if he is the owner of  the  device.   This  option  implies  the
                  options  nosuid  and  nodev  (unless  overridden  by  subsequent
                  options, as in the option line owner,dev,suid).
                  Attempt to remount an already-mounted filesystem.  This is  com-
                  monly  used  to  change  the mount flags for a filesystem, espe-
                  cially to make a readonly  filesystem  writeable.  It  does  not
                  change device or mount point.
                  options with options from command line ( -o ).
           ro     Mount the filesystem read-only.
                  Like  _netdev,  except  "fsck  -a" checks this filesystem during
           rw     Mount the filesystem read-write.
           sync   All I/O to the filesystem should be done synchronously. In  case
                  of  media  with  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 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  filesys-
                  tem.  This is the default.
           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


           The following options apply only to certain filesystems.  We sort  them
           by filesystem. They all follow the -o flag.
           What  options  are supported depends a bit on the running kernel.  More
           info  may  be  found  in  the  kernel  source  subdirectory  Documenta-

    Mount options for adfs

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

    Mount options for affs

           uid=value and gid=value
                  Set  the owner and group of the root of the filesystem (default:
           usemp  Set uid and gid of the root of the filesystem to the uid and gid
                  of the mount point upon the first sync or umount, and then clear
                  this option. Strange...
                  Print an informational message for each successful mount.
                  Prefix used before volume name, when following a link.
                  Prefix (of length at most 30) used before '/' when  following  a
                  symbolic link.
                  (Default:  2.)  Number  of  unused  blocks  at  the start of the
                  Give explicitly the location of the root block.
                  Give blocksize. Allowed values are 512, 1024, 2048, 4096.
                  These options are accepted but ignored.  (However, quota  utili-
                  ties may react to such strings in /etc/fstab.)

    Mount options for cifs

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

    Mount options for coherent


    Mount options for debugfs

           The debugfs filesystem is a pseudo filesystem, traditionally mounted on
           /sys/kernel/debug.  There are no mount options.

    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
                  of indices created in other instances of devpts.
                  All  mounts  of devpts without this newinstance option share the
                  same set of pty indices (i.e legacy mode).  Each mount of devpts
                  with the newinstance option has a private set of pty indices.
                  This  option  is  mainly used to support containers in the linux
                  kernel. It is implemented in linux kernel versions starting with
                  2.6.29.   Further,  this  mount  option  is  valid  only if CON-
                  FIG_DEVPTS_MULTIPLE_INSTANCES is enabled in the kernel  configu-
                  To  use  this  option  effectively, /dev/ptmx must be a symbolic
                  link to pts/ptmx.  See  Documentation/filesystems/devpts.txt  in
                  the linux kernel source tree for details.
                  Set the mode for the new ptmx device node in the devpts filesys-
                  With the support for multiple instances of  devpts  (see  newin-
                  stance  option  above), each instance has a private ptmx node in
                  the root of the devpts filesystem (typically /dev/pts/ptmx).
                  For compatibility with older versions of the kernel, the default
                  mode  of  the new ptmx node is 0000.  ptmxmode=value specifies a
                  more useful mode for the ptmx node  and  is  highly  recommended
                  when the newinstance option is specified.
                  This  option is only implemented in linux kernel versions start-
                  ing with 2.6.29. Further this  option  is  valid  only  if  CON-
                  FIG_DEVPTS_MULTIPLE_INSTANCES  is enabled in the kernel configu-

    Mount options for ext

           None.  Note that the 'ext' filesystem is obsolete. Don't use it.  Since
           Linux version 2.1.21 extfs is no longer part of the kernel 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 tune2fs(8).
                  Support POSIX Access Control Lists (or not).
                  Set  the  behaviour  for  the  statfs  system  call. The minixdf
                  behaviour is to return in the f_blocks field the total number of
                  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.
           debug  Print debugging info upon each (re)mount.
                  Define the behaviour when  an  error  is  encountered.   (Either
                  ignore  errors  and  just mark the filesystem erroneous and con-
                  tinue, or remount the filesystem read-only, or  panic  and  halt
                  the  system.)   The default is set in the filesystem superblock,
                  and can be changed using tune2fs(8).
           grpid|bsdgroups and nogrpid|sysvgroups
                  These options define what group id a newly  created  file  gets.
                  When  grpid  is  set,  it takes the group id of the directory in
                  which it is created; otherwise (the default) it takes the  fsgid
                  of  the current process, unless the directory has the setgid bit
                  set, in which case it takes the gid from the  parent  directory,
                  and also gets the setgid bit set if it is a directory itself.
                  These options are accepted but ignored.
           nobh   Do not attach buffer_heads to file pagecache. (Since 2.5.49.)
                  Disables  32-bit  UIDs  and  GIDs.  This is for interoperability
                  with older kernels which only store and expect 16-bit values.
           oldalloc or orlov
                  Use old allocator or Orlov allocator for new  inodes.  Orlov  is
           resgid=n and resuid=n
                  The  ext2 filesystem reserves a certain percentage of the avail-
                  able space (by default 5%, see mke2fs(8) and tune2fs(8)).  These
                  options  determine  who  can use the reserved blocks.  (Roughly:
                  whoever has the specified  uid,  or  belongs  to  the  specified
           sb=n   Instead  of  block  1,  use block n as superblock. This could be
                  useful when the filesystem has been damaged.   (Earlier,  copies
                  of  the  superblock would be made every 8192 blocks: in block 1,
                  8193, 16385, ... (and one got  thousands  of  copies  on  a  big
                  filesystem).  Since  version  1.08,  mke2fs  has  a  -s  (sparse
                  superblock) option to reduce the number of  backup  superblocks,
                  and  since  version 1.15 this is the default. Note that this may
                  mean that ext2 filesystems created by a recent mke2fs cannot  be
                  mounted  r/w  under Linux 2.0.*.)  The block number here uses 1k
                  Update the ext3 filesystem's journal to the current format.
                  When  a  journal  already exists, this option is ignored. Other-
                  wise, it specifies the number of the inode which will  represent
                  the  ext3  filesystem's  journal  file;   ext3 will create a new
                  journal, overwriting the old contents of the  file  whose  inode
                  number is inum.
                  When  the  external  journal  device's  major/minor numbers have
                  changed, this option allows the user to specify the new  journal
                  location.   The  journal  device  is  identified through its new
                  major/minor numbers encoded in devnum.
                  Don't load the journal on mounting.  Note that if the filesystem
                  was not unmounted cleanly, skipping the journal replay will lead
                  to the filesystem containing inconsistencies that  can  lead  to
                  any number of problems.
                  Specifies  the  journalling  mode  for  file  data.  Metadata is
                  always journaled.  To use modes other than ordered on  the  root
                  filesystem,  pass the mode to the kernel as boot parameter, e.g.
                         All data is committed into the  journal  prior  to  being
                         written into the main filesystem.
                         This  is  the  default mode.  All data is forced directly
                         out to the main file system prior to its  metadata  being
                         committed to the journal.
                         Data ordering is not preserved - data may be written into
                         the main filesystem after its metadata has been committed
                         to  the  journal.   This  is  rumoured to be the highest-
                         throughput option.   It  guarantees  internal  filesystem
                         integrity,  however  it  can  allow old data to appear in
                         files after a crash and journal recovery.
           barrier=0 / barrier=1
                  This enables/disables barriers.   barrier=0  disables  it,  bar-
                  rier=1 enables it.  Write barriers enforce proper on-disk order-
                  ing of journal commits, making volatile disk write  caches  safe
                  to  use,  at  some  performance  penalty.   The  ext3 filesystem
                  enables write barriers by default.  Be sure to  enable  barriers
                  unless your disks are battery-backed one way or another.  Other-
                  wise you risk filesystem corruption in case of power failure.
           porting large filesystem.
           The   options  journal_dev,  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 and [no]bh are backwardly compatible  with  ext3  or
                  Enable  checksumming  of  the  journal  transactions.  This will
                  allow the recovery code in e2fsck and the kernel to detect  cor-
                  ruption  in  the  kernel.  It is a compatible change and will be
                  ignored by older kernels.
                  Commit block can be written to disk without waiting for descrip-
                  tor  blocks.  If  enabled older kernels cannot mount the device.
                  This will enable
                  Update the ext4 filesystem's journal to the current format.
           barrier=0 / barrier=1 / barrier / nobarrier
                  This enables/disables the use of write barriers in the jbd code.
                  barrier=0 disables, barrier=1 enables.  This also requires an IO
                  stack which can support barriers, and if jbd gets an error on  a
                  barrier write, it will disable again with a warning.  Write bar-
                  riers 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.  The
                  mount options "barrier" and "nobarrier"  can  also  be  used  to
                  enable  or  disable  barriers,  for  consistency with other ext4
                  mount options.
                  The ext4 filesystem enables write barriers by default.
                  This tuning parameter controls the maximum number of inode table
                  blocks that ext4's inode table readahead algorithm will pre-read
                  into the buffer cache.  The value must be  a  power  of  2.  The
                  default value is 32 blocks.
                  Number  of  filesystem  blocks  that mballoc will try to use for
                  allocation size and alignment. For RAID5/6 systems  this  should
                  be  the  number  of  data  disks * RAID chunk size in filesystem
                  Deferring block allocation until write-out time.
                  transaction. Call this time the "commit time".  If the time that
                  the  transactoin  has been running is less than the commit time,
                  ext4 will try sleeping for the commit time to see if other oper-
                  ations  will  join the transaction. The commit time is capped by
                  the max_batch_time, which defaults to 15000us (15ms). This opti-
                  mization can be turned off entirely by setting max_batch_time to
                  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  priorty)
                  which  should be used for I/O operations submitted by kjournald2
                  during a commit operation.  This  defaults  to  3,  which  is  a
                  slightly higher priority than the default I/O priority.
           abort  Simulate  the effects of calling ext4_abort() for debugging pur-
                  poses.  This is normally  used  while  remounting  a  filesystem
                  which is already mounted.
                  Many  broken applications don't use fsync() when noauto_da_alloc
                  replacing existing files via patterns such as
                  fd =  open("")/write(fd,..)/close(fd)/  rename("",
                  or worse yet
                  fd = open("foo", O_TRUNC)/write(fd,..)/close(fd).
                  If  auto_da_alloc  is enabled, ext4 will detect the replace-via-
                  rename and replace-via-truncate  patterns  and  force  that  any
                  delayed  allocation  blocks  are allocated such that at the next
                  journal commit, in  the  default  data=ordered  mode,  the  data
                  blocks  of  the  new file are forced to disk before the rename()
                  operation is commited.  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.
                  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.
                  filesystem metadata blocks. This option is intended  for  debug-
                  ging  purposes  and since it negatively affects the performance,
                  it is off by default.
                  Controls whether or not ext4 should use the DIO read locking. If
                  the dioread_nolock option is specified ext4 will allocate unini-
                  tialized 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 nobh option and
                  the mount will fail. Nor does it 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).
                  Enable 64-bit inode version  support.  This  option  is  off  by

    Mount options for fat

           (Note:  fat  is  not  a  separate  filesystem, but a common part of the
           msdos, umsdos and vfat filesystems.)
                  Set blocksize (default 512). This option is obsolete.
           uid=value and gid=value
                  Set the owner and group of all files.  (Default: the uid and gid
                  of the current process.)
                  Set  the  umask  (the  bitmask  of  the permissions that are not
                  present). The default is the umask of the current process.   The
                  value is given in octal.
                  Set  the  umask applied to directories only.  The default is the
                  umask of the current process.  The value is given in octal.
                  Set the umask applied to regular files only.  The default is the
                  umask of the current process.  The value is given in octal.
                  This option controls the permission check of mtime/atime.
                  20     If  current  process  is in group of file's group ID, you
                         can change timestamp.
                         Upper and lower case are accepted  and  equivalent,  long
                         name   parts  are  truncated  (e.g.   verylongname.foobar
                         becomes, leading and  embedded  spaces  are
                         accepted in each name part (name and extension).
                         Like  "relaxed",  but  many  special characters (*, ?, <,
                         spaces, etc.) are rejected.  This is the default.
                         Like "normal", but names may not contain long  parts  and
                         special  characters that are sometimes used on Linux, but
                         are not accepted by MS-DOS are rejected. (+,  =,  spaces,
                  Sets  the codepage for converting to shortname characters on FAT
                  and VFAT filesystems. By default, codepage 437 is used.
                  The fat filesystem can perform CRLF<-->NL (MS-DOS text format to
                  UNIX  text  format) conversion in the kernel. The following con-
                  version modes are available:
                  binary no translation is performed.  This is the default.
                  text   CRLF<-->NL translation is performed on all files.
                  auto   CRLF<-->NL translation is performed  on  all  files  that
                         don't  have  a "well-known binary" extension. The list of
                         known  extensions  can  be  found  at  the  beginning  of
                         fs/fat/misc.c  (as  of  2.0,  the list is: exe, com, bin,
                         app, sys, drv, ovl, ovr, obj, lib, dll,  pif,  arc,  zip,
                         lha,  lzh,  zoo, tar, z, arj, tz, taz, tzp, tpz, gz, tgz,
                         deb, gif, bmp, tif, gl, jpg, pcx, tfm, vf, gf,  pk,  pxl,
                  Programs  that do computed lseeks won't like in-kernel text con-
                  version.  Several people have had  their  data  ruined  by  this
                  translation. Beware!
                  For filesystems mounted in binary mode, a conversion tool (from-
                  dos/todos) is available. This option is obsolete.
                  Forces the driver to use the CVF (Compressed Volume File) module
                  cvf_module  instead  of  auto-detection.  If the kernel supports
                  kmod, the cvf_format=xxx  option  also  controls  on-demand  CVF
                  module loading.  This option is obsolete.
                  Option passed to the CVF module. This option is obsolete.
           tz=UTC This option disables the conversion of timestamps between  local
                  time  (as  used  by  Windows  on  FAT) and UTC (which Linux uses
                  internally).  This is particularly useful when mounting  devices
                  (like digital cameras) that are set to UTC in order to avoid the
                  pitfalls of local time.
           quiet  Turn on the quiet flag.  Attempts to chown or chmod files do not
                  return errors, although they fail. Use with caution!
                  If  set, the execute permission bits of the file will be allowed
                  only if the extension part of the name is .EXE, .COM,  or  .BAT.
                  Not set by default.
                  If  set,  ATTR_SYS attribute on FAT is handled as IMMUTABLE flag
                  on Linux.  Not set by default.
           flush  If set, the filesystem will try to flush to disk more early than
                  normal.  Not set by default.
                  Use the "free clusters" value stored on FSINFO. It'll be used to
                  determine number of free clusters  without  scanning  disk.  But
                  it's not used by default, because recent Windows don't update it
                  correctly in some case. If you are sure the "free  clusters"  on
                  FSINFO is correct, by this option you can avoid scanning disk.
           dots, nodots, dotsOK=[yes|no]
                  Various misguided attempts to force Unix or DOS conventions onto
                  a FAT filesystem.

    Mount options for hfs

           creator=cccc, type=cccc
                  Set the creator/type values as shown by the  MacOS  finder  used
                  for creating new files.  Default values: '????'.
           uid=n, gid=n
                  Set the owner and group of all files.  (Default: the uid and gid
                  of the current process.)
           dir_umask=n, file_umask=n, umask=n
                  Set the umask used for all directories, all  regular  files,  or
                  all files and directories.  Defaults to the umask of the current
                  Select the CDROM session to mount.   Defaults  to  leaving  that
                  decision  to  the CDROM driver.  This option will fail with any-
                  thing but a CDROM as underlying device.
                  value is given in octal.
                  Convert all files names to lower case, or leave them.  (Default:
                  For  conv=text,  delete some random CRs (in particular, all fol-
                  lowed by NL) when reading a file.  For conv=auto, choose more or
                  less   at   random   between  conv=binary  and  conv=text.   For
                  conv=binary, just read what is in the file. This is the default.
                  Do not abort mounting when certain consistency checks fail.

    Mount options for iso9660

           ISO  9660 is a standard describing a filesystem structure to be used on
           CD-ROMs. (This filesystem type is also seen on some DVDs. See also  the
           udf filesystem.)
           Normal  iso9660  filenames  appear  in  a  8.3  format  (i.e., DOS-like
           restrictions on filename length), and in addition all characters are in
           upper  case.   Also  there  is no field for file ownership, protection,
           number of links, provision for block/character devices, etc.
           Rock Ridge is an extension to iso9660 that provides all of  these  unix
           like features.  Basically there are extensions to each directory record
           that supply all of the additional information, and when Rock  Ridge  is
           in use, the filesystem is indistinguishable from a normal UNIX filesys-
           tem (except that it is read-only, of course).
           norock Disable the use of Rock Ridge extensions, even if available. Cf.
                  Disable  the  use of Microsoft Joliet extensions, even if avail-
                  able. Cf. map.
                  With check=relaxed, a filename is first converted to lower  case
                  before  doing  the  lookup.   This  is  probably only meaningful
                  together with norock and map=normal.  (Default: check=strict.)
           uid=value and gid=value
                  Give all files in the filesystem the indicated user or group id,
                  possibly  overriding  the  information  found  in the Rock Ridge
                  extensions.  (Default: uid=0,gid=0.)
                  For non-Rock Ridge volumes, normal name translation  maps  upper
                  to  lower case ASCII, drops a trailing ';1', and converts ';' to
                  Set   the   block   size  to  the  indicated  value.   (Default:
                  (Default: conv=binary.)  Since Linux 1.3.54 this option  has  no
                  effect  anymore.   (And non-binary settings used to be very dan-
                  gerous, possibly leading to silent data corruption.)
           cruft  If the high byte of the file length contains other garbage,  set
                  this  mount  option  to  ignore  the high order bits of the file
                  length.  This implies that a file cannot be larger than 16MB.
                  Select number of session on multisession CD. (Since 2.3.4.)
                  Session begins from sector xxx. (Since 2.3.4.)
           The following options are the same as for vfat and specifying them only
           makes  sense  when  using discs encoded using Microsoft's Joliet exten-
                  Character set to use for converting 16 bit Unicode characters on
                  CD to 8 bit characters. The default is iso8859-1.
           utf8   Convert 16 bit Unicode characters on CD to UTF-8.

    Mount options for jfs

                  Character  set to use for converting from Unicode to ASCII.  The
                  default is to do no conversion.   Use  iocharset=utf8  for  UTF8
                  translations.   This  requires  CONFIG_NLS_UTF8 to be set in the
                  kernel .config file.
                  Resize the volume to value blocks. JFS only supports  growing  a
                  volume,  not  shrinking  it.  This option is only valid during a
                  remount, when the volume is mounted read-write. The resize  key-
                  word  with no value will grow the volume to the full size of the
                  Do not write to the journal.  The primary use of this option  is
                  to  allow  for  higher  performance when restoring a volume from
                  backup media. The integrity of the volume is not  guaranteed  if
                  the system abnormally abends.
                  Default.   Commit  metadata  changes  to  the journal.  Use this

    Mount options for msdos

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

    Mount options for ncpfs

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

    Mount options for nfs and nfs4

           See  the options section of the nfs(5) man page (nfs-utils package must
           be installed).
           The nfs and nfs4 implementation expects a  binary  argument  (a  struct
           nfs_mount_data)  to the mount system call. This argument is constructed
           by mount.nfs(8) and the current version of mount (2.13) does  not  know
           anything about nfs and nfs4.

    Mount options for ntfs

                  Character  set  to  use when returning file names.  Unlike VFAT,
                  NTFS suppresses names  that  contain  unconvertible  characters.
                  New name for the option earlier called iocharset.
           utf8   Use UTF-8 for converting file names.
                  For  0  (or  'no'  or  'false'), do not use escape sequences for
                  unknown Unicode characters.  For 1 (or 'yes' or  'true')  or  2,
                  use vfat-style 4-byte escape sequences starting with ":". Here 2
                  give a little-endian encoding  and  1  a  byteswapped  bigendian
                  If enabled (posix=1), the filesystem distinguishes between upper
                  and lower case. The 8.3 alias names are presented as hard  links
                  instead of being suppressed. This option is obsolete.
           uid=value, gid=value and umask=value
                  Set  the  file permission on the filesystem.  The umask value is
                  given in octal.  By default, the files are owned by root and not

    Mount options for reiserfs

           Reiserfs is a journaling filesystem.
           conv   Instructs version 3.6 reiserfs software to mount a  version  3.5
                  filesystem, using the 3.6 format for newly created objects. This
                  filesystem will no longer be compatible with reiserfs 3.5 tools.
                  Choose  which  hash  function  reiserfs  will  use to find files
                  within directories.
                         A hash invented by Yury Yu. Rupasov.  It is fast and pre-
                         serves  locality,  mapping  lexicographically  close file
                         names to close hash values.  This option  should  not  be
                         used, as it causes a high probability of hash collisions.
                  tea    A   Davis-Meyer   function    implemented    by    Jeremy
                         Fitzhardinge.   It  uses hash permuting bits in the name.
                         It gets high randomness and, therefore,  low  probability
                         of hash collisions at some CPU cost.  This may be used if
                         EHASHCOLLISION errors are experienced with the r5 hash.
                  r5     A modified version of the rupasov hash.  It  is  used  by
                         default  and is the best choice unless the filesystem has
                         huge directories and unusual file-name patterns.
                  detect Instructs mount to detect which hash function is  in  use
                         by  examining the filesystem being mounted,  and to write
                         this information into the reiserfs  superblock.  This  is
                         only  useful on the first mount of an old format filesys-
                  Tunes the block allocator. This may provide performance improve-
                  ments in some situations.
                  Tunes the block allocator. This may provide performance improve-
                  ments in some situations.
                  Disable the border allocator  algorithm  invented  by  Yury  Yu.
                  Rupasov.  This may provide performance improvements in some sit-
           nolog  Disable  journalling.  This  will  provide  slight   performance
                  improvements in some situations at the cost of losing reiserfs's
                  fast recovery from crashes.  Even with this  option  turned  on,
                  reiserfs  still  performs  all  journalling operations, save for
                  actual writes into  its  journalling  area.   Implementation  of
                  ber  blocks.  This option is designed for use with devices which
                  are under logical volume management (LVM).  There is  a  special
                  resizer     utility     which     can     be    obtained    from
                  Enable Extended User Attributes. See the attr(5) manual page.
           acl    Enable POSIX Access Control Lists. See the acl(5) manual page.
           barrier=none / barrier=flush
                  This enables/disables the use of write barriers in the  journal-
                  ing  code.   barrier=none disables it, barrier=flush enables it.
                  Write barriers enforce proper on-disk ordering of  journal  com-
                  mits,  making  volatile  disk  write caches safe to use, at some
                  performance penalty. The reiserfs  filesystem  does  not  enable
                  write  barriers  by  default.  Be sure to enable barriers unless
                  your disks are battery-backed one way or another. Otherwise  you
                  risk filesystem corruption in case of power failure.

    Mount options for romfs


    Mount options for squashfs


    Mount options for smbfs

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

    Mount options for sysv


    Mount options for tmpfs

                  Override default maximum size of the filesystem.   The  size  is
                  given  in bytes, and rounded up to entire pages.  The default is
                  half of the memory. The size parameter also accepts a  suffix  %
                  to limit this tmpfs instance to that percentage of your physical
                  RAM: the default, when neither size nor nr_blocks is  specified,
                  is size=50%
                  The same as size, but in blocks of PAGE_CACHE_SIZE
           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-separated decimal numbers,
                  the smallest and largest node numbers in the range.   For  exam-
                  ple, mpol=bind:0-3,5,7,9-15
                  Note  that trying to mount a tmpfs with an mpol option will fail
                  if the running kernel does not support NUMA; and  will  fail  if
                  its nodelist specifies a node which is not online.  If your sys-
                  tem relies on that tmpfs being mounted, but from  time  to  time
                  runs  a  kernel  built  without  NUMA capability (perhaps a safe
                  recovery kernel), or with fewer nodes online, then it is  advis-
                  able  to  omit the mpol option from automatic mount options.  It
                  can be added later, when the tmpfs is already mounted on  Mount-
                  Point, by 'mount -o remount,mpol=Policy:NodeList MountPoint'.

    Mount options for ubifs

           UBIFS  is  a  flash file system which works on top of UBI volumes. Note
           that atime is not supported and is always turned off.
           The device name may be specified as
                  ubiX_Y UBI device number X, volume number Y
                  ubiY   UBI device number 0, volume number Y
                         UBI device number X, volume with name NAME
                  Check data CRC-32 checksums. This is the default.
                  Do not check  data  CRC-32  checksums.  With  this  option,  the
                  filesystem  does not check CRC-32 checksum for data, but it does
                  check it for the internal indexing information. This option only
                  affects  reading,  not writing. CRC-32 is always calculated when
                  writing the data.
                  Select the default compressor which is used when new  files  are
                  written.  It  is  still  possible  to  read  compressed files if
                  mounted with the none option.

    Mount options for udf

           udf is the "Universal Disk Format" filesystem defined  by  the  Optical
           Storage  Technology  Association,  and  is often used for DVD-ROM.  See
           also iso9660.
           gid=   Set the default group.
           umask= Set the default umask.  The value is given in octal.
           uid=   Set the default user.
           unhide Show otherwise hidden files.
                  Show deleted files in lists.
                  Unset strict conformance.
                  Set the NLS character set.
           bs=    Set the block size. (May not work unless 2048.)
           novrs  Skip volume sequence recognition.
                  Set the CDROM session counting from 0. Default: last session.
                  Override standard anchor location. Default: 256.
                  Override the VolumeDesc location. (unused)
                  UFS is a filesystem widely used in different operating  systems.
                  The  problem  are differences among implementations. Features of
                  some implementations are undocumented, so its hard to  recognize
                  the type of ufs automatically.  That's why the user must specify
                  the type of ufs by mount option.  Possible values are:
                  old    Old format of  ufs,  this  is  the  default,  read  only.
                         (Don't forget to give the -r option.)
                  44bsd  For    filesystems   created   by   a   BSD-like   system
                  sun    For filesystems created by SunOS or Solaris on Sparc.
                  sunx86 For filesystems created by Solaris on x86.
                  hp     For filesystems created by HP-UX, read-only.
                         For filesystems created by  NeXTStep  (on  NeXT  station)
                         (currently read only).
                         For NextStep CDROMs (block_size == 2048), read-only.
                         For  filesystems  created  by  OpenStep  (currently  read
                         only).  The same filesystem type is also used by  Mac  OS
                  Set behaviour on error:
                  panic  If an error is encountered, cause a kernel panic.
                         These mount options don't do anything at present; when an
                         error is encountered only a console message is printed.

    Mount options for umsdos

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

    Mount options for vfat

           First  of  all,  the  mount options for fat are recognized.  The dotsOK
           option is explicitly killed by vfat.  Furthermore, there are
           utf8   UTF8 is the filesystem safe 8-bit encoding of  Unicode  that  is
                  used  by  the  console.  It can be 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  behaviour  for  creation  and display of filenames
                  which fit into 8.3 characters. If a long name for a file exists,
                  it will always be preferred 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. This
                         mode is the default.
                  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 shortname 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.

    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-
                  reflect this format being in use.
                  The  default  behavior  is determined by the on-disk feature bit
                  indicating that attr2  behavior  is  active.   If  either  mount
                  option  it  set,  then  that becomes the new default used by the
                  CRC enabled filesystems always use the attr2 format, and so will
                  reject the noattr2 mount option if it is set.
                  Enables/disables  the  use  of  block  layer  write barriers for
                  writes into the journal and for data integrity operations.  This
                  allows  for drive level write caching to be enabled, for devices
                  that support write barriers.
                  Enable/disable the issuing of commands to let the  block  device
                  reclaim  space  freed by the filesystem.  This is useful for SSD
                  devices, thinly provisioned LUNs and virtual machine images, but
                  may have a performance impact.
                  Note: It is currently recommended that you use the fstrim appli-
                  cation to discard unused blocks rather than  the  discard  mount
                  option  because  the  performance impact of this option is quite
                  These options define what group ID a newly  created  file  gets.
                  When  grpid  is  set,  it takes the group ID of the directory in
                  which it is created; otherwise it takes the fsgid of the current
                  process,  unless  the directory has the setgid bit set, in which
                  case it takes the gid from the parent directory, and  also  gets
                  the setgid bit set if it is a directory itself.
                  Make  the  data  allocator  use  the filestreams allocation mode
                  across the entire filesystem rather  than  just  on  directories
                  configured to use it.
                  When  ikeep  is specified, XFS does not delete empty inode clus-
                  ters and keeps them around on disk.  When noikeep is  specified,
                  empty inode clusters are returned to the free space pool.
                  When  inode32  is  specified, it indicates that XFS limits inode
                  creation to locations which will not  result  in  inode  numbers
                  with more than 32 bits of significance.
                  When  inode64  is specified, it indicates that XFS is allowed to
                  create inodes at any location in the filesystem, including those
                  is typically the page size of the machine, as this is the granu-
                  larity of the page cache.
                  If  "largeio"  specified,  a  filesystem that was created with a
                  "swidth" specified will return the "swidth" value (in bytes)  in
                  st_blksize.   If  the filesystem does not have a "swidth" speci-
                  fied but does specify an "allocsize" then "allocsize" (in bytes)
                  will be returned instead.  Otherwise the behavior is the same as
                  if "nolargeio" was specified.
                  Set the number of in-memory log buffers.   Valid  numbers  range
                  from 2-8 inclusive.
                  The default value is 8 buffers.
                  If  the  memory  cost of 8 log buffers is too high on small sys-
                  tems, then it may be reduced at  some  cost  to  performance  on
                  metadata  intensive  workloads.   The logbsize option below con-
                  trols the size of each buffer and so is also  relevant  to  this
                  Set  the  size  of  each  in-memory log buffer.  The size may be
                  specified in bytes, or in kibibytes (KiB)  with  a  "k"  suffix.
                  Valid  sizes  for  version  1  and  version  2  logs  are  16384
                  (value=16k) and 32768 (value=32k).  Valid sizes  for  version  2
                  logs  also  include  65536  (value=64k), 131072 (value=128k) and
                  262144 (value=256k).  The logbsize must be an  integer  multiple
                  of the log stripe unit configured at mkfs time.
                  The default value for version 1 logs is 32768, while the default
                  value for version 2 logs is MAX(32768, log_sunit).
           logdev=device and rtdev=device
                  Use an external log (metadata journal) and/or real-time  device.
                  An  XFS  filesystem has up to three parts: a data section, a log
                  section, and a real-time  section.   The  real-time  section  is
                  optional, and the log section can be separate from the data sec-
                  tion or contained within it.
                  Data allocations will not be aligned at stripe unit  boundaries.
                  This  is only relevant to filesystems created with non-zero data
                  alignment parameters (sunit, swidth) by mkfs.
                  The filesystem will be mounted without running log recovery.  If
                  the  filesystem  was  not  cleanly unmounted, it is likely to be
                  inconsistent when mounted in "norecovery" mode.  Some  files  or
                  directories  may not be accessible because of this.  Filesystems
                  mounted "norecovery" must be mounted read-only or the mount will
                  Group disk quota  accounting  enabled  and  limits  (optionally)
                  enforced.  Refer to xfs_quota(8) for further details.
                  Project  disk  quota  accounting enabled and limits (optionally)
                  enforced.  Refer to xfs_quota(8) for further details.
           sunit=value and swidth=value
                  Used to specify the stripe unit and width for a RAID device or a
                  stripe  volume.   "value"  must  be  specified in 512-byte block
                  units.  These options are only relevant to filesystems that were
                  created with non-zero data alignment parameters.
                  The  sunit  and  swidth  parameters specified must be compatible
                  with the existing filesystem alignment characteristics.  In gen-
                  eral,  that means the only valid changes to sunit are increasing
                  it by a power-of-2 multiple.  Valid swidth values are any  inte-
                  ger multiple of a valid sunit value.
                  Typically  the  only  time  these mount options are necessary if
                  after an underlying RAID device has had it's geometry  modified,
                  such as adding a new disk to a RAID5 lun and reshaping it.
                  Data  allocations  will be rounded up to stripe width boundaries
                  when the current end of file is being extended and the file size
                  is larger than the stripe width size.
           wsync  When specified, all filesystem namespace operations are executed
                  synchronously.  This ensures that when the  namespace  operation
                  (create,  unlink, etc) completes, the change to the namespace is
                  on stable storage.  This is useful in HA setups  where  failover
                  must not result in clients seeing inconsistent namespace presen-
                  tation during or after a failover event.

    Mount options for xiafs

           None. Although nothing is wrong with xiafs, it is not used much, and is
           not  maintained.  Probably  one  shouldn't use it.  Since Linux version
           2.1.21 xiafs is no longer part of the kernel source.


           One further possible type is a mount via the loop device. For  example,
           the command
             mount /tmp/fdimage /mnt -t vfat -o loop=/dev/loop3
           will  set  up  the  loop  device  /dev/loop3  to correspond to the file
           /tmp/fdimage, and then mount this device on /mnt.
           You  can also free a loop device by hand, using 'losetup -d' or 'umount


           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 syntax of external mount helpers is:
                  /sbin/mount.<suffix> spec dir [-sfnv] [-o options] [-t type.sub-
           where  the <type> is filesystem type and -sfnvo options have same mean-
           ing like standard mount options. The -t option is used  for filesystems
           with subtypes support (for example /sbin/mount.fuse -t fuse.sshfs).


           /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


           mount(2),  umount(2),  fstab(5),  umount(8), swapon(8), nfs(5), xfs(5),
           e2label(8), xfs_admin(8), mountd(8),  nfsd(8),  mke2fs(8),  tune2fs(8),
           It  is  possible that files /etc/mtab and /proc/mounts don't match. 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.)
           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


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


           The mount command is part of the util-linux-ng package and is available

    Linux 2.6 2004-12-16 MOUNT(8)


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