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MOUNT(8)                   Linux Programmer's Manual                  MOUNT(8)



NAME
       mount - mount a filesystem

SYNOPSIS
       mount [-lhV]

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

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

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

DESCRIPTION
       All  files accessible in a Unix system are arranged in one big tree, the file hier-
       archy, rooted at /.  These files can be spread out over several devices. The  mount
       command  serves to attach the filesystem found on some device to the big file tree.
       Conversely, the umount(8) command will detach it again.

       The standard form of the mount command, is

              mount -t type device dir

       This tells the kernel to attach the filesystem found on device (which  is  of  type
       type)  at  the directory dir.  The previous contents (if any) and owner and mode of
       dir become invisible, and as long as this filesystem remains mounted, the  pathname
       dir refers to the root of the filesystem on device.

       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 knuth.cwi.nl:/dir.  It is possible to  indi-
              cate  a  block special device using its volume LABEL or UUID (see the -L and
              -U options below).

              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
              LABEL=/UUID=.  For more details see libblkid(3).

              The proc filesystem is not associated with a special device, and when mount-
              ing  it,  an arbitrary keyword, such as proc can be used instead of a device
              specification.  (The customary choice none is less fortunate: the error mes-
              sage '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 command

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

              (usually given in a bootscript) causes all filesystems  mentioned  in  fstab
              (of  the  proper  type and/or having or not having the proper options) to be
              mounted as indicated, except for those whose line contains the  noauto  key-
              word. 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  give
              only the device, or only the mount point.


              The  programs mount and umount maintain a list of currently mounted filesys-
              tems 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 former has somewhat more infor-
              mation, 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 sys-
              tem.

              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  com-
              mand

                     mount /dev/cdrom

              or

                     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,  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 con-
              sole 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 some-
              where 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 possible sub-
              mounts. 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 example:

                     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 submounts as
              shared, private, slave or unbindable. A shared  mount  provides  ability  to
              create  mirrors of that mount such that mounts and umounts within any of the
              mirrors propagate to the other mirror. A slave  mount  receives  propagation
              from  its master, but any not vice-versa.  A private mount carries no propa-
              gation abilities.  A unbindable mount is a private mount which cannot cloned
              through  a  bind  operation.  Detailed semantics is documented in Documenta-
              tion/sharedsubtree.txt file in the kernel source tree.

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

              The following commands allows 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


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

       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 unde-
              fined order.  Thus, you cannot use this option if you  want  to  mount  both
              /usr and /usr/spool.

       -f, --fake
              Causes  everything to be done except for the actual system call; if it's not
              obvious, this ''fakes'' mounting the filesystem.  This option is  useful  in
              conjunction  with  the -v flag to determine what the mount command is trying
              to do. It can also be used to add entries for devices that were mounted ear-
              lier  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 exists.

       -l     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.

       --no-canonicalize
              Don't  canonicalize  paths.  The mount command canonicalizes all paths (from
              command line or fstab) and stores canonicalized paths to the /etc/mtab file.
              This  option can be used together with the -f flag for already canonicalized
              absolut paths.

       -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 auto-
              mounter.

       -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 usbde-
              vfs.   Note, the real list of all supported filesystems depends on your ker-
              nel.

              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 'sshfs#example.com' is depreacated).

              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) ad hoc code is
              necessary. The nfs, nfs4, cifs, smbfs, and ncpfs filesystems have a separate
              mount  program. In order to make it possible to treat all types in a uniform
              way, mount will execute the program /sbin/mount.TYPE (if that  exists)  when
              called  with type TYPE.  Since various versions of the smbmount program have
              different calling conventions, /sbin/mount.smbfs may  have  to  be  a  shell
              script that sets up the desired call.

              If  no  -t option is given, or if the auto type is specified, mount will try
              to guess the desired type.  Mount uses the blkid 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 recognize the wrong filesystem type,  possibly  with  catastrophic
              consequences. If your data is valuable, don't ask mount to guess.

              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 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
              Options are specified with a -o flag followed by a comma separated string of
              options. For example:

                     mount LABEL=mydisk -o noatime,nouser


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

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

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

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


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

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

       The following options apply to any filesystem that is being mounted (but not  every
       filesystem  actually  honors them - e.g., the sync option today has 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 controlled by ker-
              nel defaults. See also the description for strictatime  and  relatime  mount
              options.

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

       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 format-
              ted 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 compatibil-
              ity 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=sys-
              tem_u:object_r:removable_t.

              Two other options are fscontext= and defcontext=, both of which are mutually
              exclusive of the context option. This means you can use fscontext  and  def-
              context 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 indi-
              vidual labels on the files. It represents the entire filesystem for  certain
              kinds of permission checks, such as during mount or file creation.  Individ-
              ual file labels are still obtained from the xattrs on the files  themselves.
              The  context  option actually sets the aggregate context that fscontext pro-
              vides, in addition to supplying the same label for individual files.

              You can set the default security context for unlabeled files  using  defcon-
              text= 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 because visable to userspace. This
              was found to be useful for things like stateless linux.

              For more details, see selinux(8)


       defaults
              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 system.

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

       nodiratime
              Do not update directory inode access times on this filesystem.

       dirsync
              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  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 by subsequent options, as in the option
              line group,dev,suid).

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

       noiversion
              Do not increment the i_version inode field.

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

       nomand Do not allow mandatory locks on this filesystem.

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

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

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

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

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

       strictatime
              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.

       nostrictatime
              Use the kernel's default behaviour 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. (This seems safe, but is in fact rather unsafe  if  you  have  suid-
              perl(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).

       remount
              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 writeable. It does not change device or mount point.

              The remount functionality follows the standard way  how  the  mount  command
              works with options from fstab. It means the mount command doesn't read fstab
              (or mtab) only when a device and dir are fully 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
              options from command line ( -o ).

       ro     Mount the filesystem read-only.

       _rnetdev
              Like _netdev, except "fsck -a" checks this filesystem during rc.sysinit.

       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 filesystem.   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 users,exec,dev,suid).


FILESYSTEM SPECIFIC MOUNT OPTIONS
       The  following options apply only to certain filesystems.  We sort them by filesys-
       tem. 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'  permis-
              sions,  respectively  (default:  0700  and  0077,  respectively).   See also
              /usr/src/linux/Documentation/filesystems/adfs.txt.

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

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

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

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

       verbose
              Print an informational message for each successful mount.

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

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

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

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

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

       grpquota|noquota|quota|usrquota
              These options are accepted but ignored.  (However, quota utilities 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 package  must  be
       installed).


Mount options for coherent
       None.


Mount options for debugfs
       The  debugfs  filesystem is a pseudo filesystem, traditionally mounted on /sys/ker-
       nel/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 /dev/pts/<number>.

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

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

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

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

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

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

       ptmxmode=value

              Set the mode for the new ptmx device node in the devpts 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 (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 speci-
              fied.

              This option is only implemented  in  linux  kernel  versions  starting  with
              2.6.29.   Further   this   option  is  valid  only  if  CONFIG_DEVPTS_MULTI-
              PLE_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  ver-
       sion 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).

       acl|noacl
              Support POSIX Access Control Lists (or not).

       bsddf|minixdf
              Set  the  behaviour  for the statfs system call. The minixdf behaviour is to
              return in the f_blocks field the total number of blocks of  the  filesystem,
              while the bsddf behaviour (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|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.

       debug  Print debugging info upon each (re)mount.

       errors={continue|remount-ro|panic}
              Define the behaviour when an error is encountered.   (Either  ignore  errors
              and just mark the filesystem erroneous and continue, or remount the filesys-
              tem 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.

       grpquota|noquota|quota|usrquota
              These options are accepted but ignored.

       nobh   Do not attach buffer_heads to file pagecache. (Since 2.5.49.)

       nouid32
              Disables 32-bit UIDs and GIDs.  This is for interoperability with older ker-
              nels 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 specified group.)

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

       user_xattr|nouser_xattr
              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  journalling.   It  supports the same options as ext2 as well as the following
       additions:

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

       journal=inum
              When a journal already exists, this option is ignored. Otherwise, it  speci-
              fies  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.

       journal_dev=devnum
              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.

       norecovery/noload
              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.

       data={journal|ordered|writeback}
              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.  rootflags=data=journal.

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

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

              writeback
                     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, barrier=1 enables
              it.  Write barriers enforce proper on-disk ordering of journal commits, mak-
              ing  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.  Otherwise
              you risk filesystem corruption in case of power failure.

       commit=nrsec
              Sync all data and metadata every nrsec seconds. The default value is 5  sec-
              onds. Zero means default.

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

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


Mount options for ext4
       The  ext4  filesystem is an an advanced level of the ext3 filesystem which incorpo-
       rates scalability and reliability enhancements for supporting 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 sysv-
       groups, resgid, resuid, sb, quota, noquota, grpquota, usrquota and [no]bh are back-
       wardly compatible with ext3 or ext2.

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

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

       journal=update
              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 sup-
              port barriers, and if jbd gets an error on a barrier write, it will  disable
              again  with  a  warning.   Write barriers enforce proper on-disk ordering of
              journal commits, making volatile disk write caches safe to use, at some per-
              formance  penalty.   If your disks are battery-backed in one way or another,
              disabling barriers may safely improve performance.  The mount options  "bar-
              rier"  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.

       inode_readahead_blks=n
              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.

       stripe=n
              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.

       delalloc
              Deferring block allocation until write-out time.

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

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

       min_batch_time=usec
              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.

       journal_ioprio=prio
              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 opera-
              tion.  This defaults to 3, which is a  slightly  higher  priority  than  the
              default I/O priority.

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

       auto_da_alloc|noauto_da_alloc
              Many broken applications don't use fsync()  when  noauto_da_alloc  replacing
              existing files via patterns 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 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.

       discard/nodiscard
              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.

       nouid32
              Disables  32-bit  UIDs  and GIDs.  This is for interoperability  with  older
              kernels which only store and expect 16-bit values.

       resize Allows to resize filesystem to the end of the  last  existing  block  group,
              further  resize  has to be done with resize2fs either online, or offline. It
              can be used only with conjunction with remount.

       block_validity/noblock_validity
              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.

       dioread_lock/dioread_nolock
              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 com-
              pletes.  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).

       i_version
              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 filesystems.)

       blocksize={512|1024|2048}
              Set blocksize (default 512). This option is obsolete.

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

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

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

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

       allow_utime=value
              This option controls the permission check of mtime/atime.

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

              2      Other users can change timestamp.

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

              Normally  utime(2)  checks  current  process is owner of the file, or it has
              CAP_FOWNER capability.  But FAT filesystem doesn't have uid/gid on disk,  so
              normal check is too unflexible. With this option you can relax it.

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

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

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

              s[trict]
                     Like "normal", but names may not contain long parts and special char-
                     acters that are sometimes used on Linux, but are not accepted by  MS-
                     DOS are rejected. (+, =, spaces, etc.)

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

       conv={b[inary]|t[ext]|a[uto]}
              The fat filesystem can perform CRLF<-->NL (MS-DOS text format to  UNIX  text
              format)  conversion in the kernel. The following conversion modes are avail-
              able:

              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, dvi).

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

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

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

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

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

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

       iocharset=value
              Character set to use for converting between 8 bit characters and 16 bit Uni-
              code characters. The default is iso8859-1.  Long  filenames  are  stored  on
              disk in Unicode format.

       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 par-
              ticularly  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!

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

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

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

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

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


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

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

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

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

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

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

       conv={binary|text|auto}
              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 default.

       nocheck
              Do not abort mounting when certain consistency checks fail.


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

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

       Rock  Ridge  is  an  extension to iso9660 that provides all of these unix like fea-
       tures.  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 indis-
       tinguishable 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.

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

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

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

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

       mode=value
              For  non-Rock  Ridge  volumes, give all files the indicated mode.  (Default:
              read permission for everybody.)  Since Linux 2.1.37 one no longer  needs  to
              specify the mode in decimal. (Octal is indicated by a leading 0.)

       unhide Also show hidden and associated files.  (If the ordinary files and the asso-
              ciated or hidden files have the same filenames, this may make  the  ordinary
              files inaccessible.)

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

       conv={a[uto]|b[inary]|m[text]|t[ext]}
              (Default:  conv=binary.)   Since Linux 1.3.54 this option has no effect any-
              more.  (And non-binary settings used to be very dangerous, possibly  leading
              to silent data corruption.)

       cruft  If  the  high byte of the file length contains other garbage, set this mount
              option to ignore the high order bits of the file length.  This implies  that
              a file cannot be larger than 16MB.

       session=x
              Select number of session on multisession CD. (Since 2.3.4.)

       sbsector=xxx
              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.

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

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


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

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

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

       integrity
              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.

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

       noquota|quota|usrquota|grpquota
              These options are accepted but ignored.


Mount options for minix
       None.


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
       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 constructed by ncp-
       mount(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 cur-
       rent version of mount (2.13) does not know anything about nfs and nfs4.


Mount options for ntfs
       iocharset=name
              Character set to use when returning file  names.   Unlike  VFAT,  NTFS  sup-
              presses names that contain unconvertible characters. Deprecated.

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

       utf8   Use UTF-8 for converting file names.

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

       posix=[0|1]
              If enabled (posix=1), the filesystem distinguishes between upper  and  lower
              case.  The 8.3 alias names are presented as hard links instead of being sup-
              pressed. 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 compatible with reiserfs 3.5 tools.

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

              rupasov
                     A hash invented by Yury Yu. Rupasov.  It is fast and preserves local-
                     ity, 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, there-
                     fore,  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 filesystem.

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

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

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

       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.  Implementa-
              tion of nolog is a work in progress.

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

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

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

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

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

       barrier=none / barrier=flush
              This  enables/disables  the  use  of  write barriers in the journaling code.
              barrier=none disables it, barrier=flush enables it. Write  barriers  enforce
              proper  on-disk  ordering  of  journal  commits,  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
       None.


Mount options for squashfs
       None.


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  smb-
       mount(8)  and  the  current  version  of  mount (2.12) does not know anything about
       smbfs.


Mount options for sysv
       None.


Mount options for tmpfs
       size=nbytes
              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%

       nr_blocks=
              The same as size, but in blocks of PAGE_CACHE_SIZE

       nr_inodes=
              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  suf-
       fix  k,  m  or  g for Ki, Mi, Gi (binary kilo, mega and giga) and can be changed on
       remount.


       mode=  Set initial permissions of the root directory.

       uid=   The user id.

       gid=   The group id.

       mpol=[default|prefer:Node|bind:NodeList|interleave|interleave:NodeList]
              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 ...'

              default
                     prefers to allocate memory from the local node

              prefer:Node
                     prefers to allocate memory from the given Node

              bind:NodeList
                     allocates memory only from nodes in NodeList

              interleave
                     prefers to allocate from each node in turn

              interleave:NodeList
                     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 example, mpol=bind:0-3,5,7,9-15

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

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

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

       The following mount options are available:

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

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

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

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

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


Mount options for udf
       udf  is the "Universal Disk Format" filesystem defined by the Optical Storage Tech-
       nology 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.

       undelete
              Show deleted files in lists.

       nostrict
              Unset strict conformance.

       iocharset
              Set the NLS character set.

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

       novrs  Skip volume sequence recognition.

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

       anchor=
              Override standard anchor location. Default: 256.

       volume=
              Override the VolumeDesc location. (unused)

       partition=
              Override the PartitionDesc location. (unused)

       lastblock=
              Set the last block of the filesystem.

       fileset=
              Override the fileset block location. (unused)

       rootdir=
              Override the root directory location. (unused)


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

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

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

              sun    For filesystems created by SunOS or Solaris on Sparc.

              sunx86 For filesystems created by Solaris on x86.

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

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

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

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


       onerror=value
              Set behaviour on error:

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

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


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


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

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

       posix  Allow  two  files with names that only differ in case.  This option is obso-
              lete.

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

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

       shortname={lower|win95|winnt|mixed}

              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 pre-
              ferred 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
       None.


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

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

       attr2|noattr2
              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.

       barrier|nobarrier
              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.

       discard|nodiscard
              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.

       grpid|bsdgroups|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; other-
              wise 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.

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

       ikeep|noikeep
              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.

       inode32|inode64
              When  inode32  is  specified, it indicates that XFS limits inode creation to
              locations which will not result in inode numbers with more than 32  bits  of
              significance.

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

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

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

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

       logbufs=value
              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.

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

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

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

       noalign
              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.

       norecovery
              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 accessi-
              ble because of this.  Filesystems 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 "norecovery" for mounting read-only snapshots.

       noquota
              Forcibly  turns off all quota accounting and enforcement within the filesys-
              tem.

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

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

       pquota/prjquota/pqnoenforce
              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 vol-
              ume.  "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 exist-
              ing  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 under-
              lying RAID device has had it's geometry modified, such as adding a new  disk
              to a RAID5 lun and reshaping it.

       swalloc
              Data allocations will be rounded up to stripe width boundaries when the cur-
              rent 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 syn-
              chronously.  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  incon-
              sistent namespace presentation 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 main-
       tained. Probably one shouldn't use it.  Since Linux  version  2.1.21  xiafs  is  no
       longer part of the kernel source.


THE LOOP DEVICE
       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.

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

       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.

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

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


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

       0      success

       1      incorrect invocation or permissions

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

       4      internal mount bug

       8      user interrupt

       16     problems writing or locking /etc/mtab

       32     mount failure

       64     some mount succeeded


NOTES
       The syntax of external mount helpers is:

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

       where the <type> is filesystem type and -sfnvo options have same meaning like stan-
       dard  mount  options.  The -t option is used  for filesystems with subtypes support
       (for example /sbin/mount.fuse -t fuse.sshfs).


FILES
       /etc/fstab        filesystem table

       /etc/mtab         table of mounted filesystems

       /etc/mtab~        lock file

       /etc/mtab.tmp     temporary file

       /etc/filesystems  a list of filesystem types to try


SEE ALSO
       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), losetup(8)

BUGS
       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).

       Mount  by  label  or  uuid  will work only if your devices have the names listed in
       /proc/partitions.  In particular, it may well fail if the kernel was compiled  with
       devfs but devfs is not mounted.

       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 used.

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

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




Linux 2.6                         2004-12-16                          MOUNT(8)

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