MOUNT(8)                                                     System Administration                                                    MOUNT(8)


       mount - mount a filesystem


       mount [-lhV]

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

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

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


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

       The standard form of the mount command, is

              mount -t type device dir

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

       If only directory or device is given, for example:

              mount /dir

       then mount looks for a mountpoint and if not found then for a device in the /etc/fstab file.

       The listing and help.
              Three forms of invocation do not actually mount anything:

              mount -h
                     prints a help message

              mount -V
                     prints a version string

              mount [-l] [-t type]
                     lists all mounted filesystems (of type type).  The option -l adds the labels in this listing.  See below.

       The device indication.
              Most  devices  are  indicated by a file name (of a block special device), like /dev/sda1, but there are other possibilities. For
              example, in the case of an NFS mount, device may look like  It is possible to indicate a block special device
              using its volume LABEL or UUID (see the -L and -U options 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 has no advantage over LABEL=/UUID=.  For more details see libblkid(3).

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

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

       The /etc/fstab, /etc/mtab and /proc/mounts files.
              The file /etc/fstab (see fstab(5)), may contain lines describing what devices are usually mounted where, using which options.

              The command

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

              (usually given in a bootscript) causes all filesystems mentioned in fstab (of the proper type and/or having or  not  having  the
              proper  options)  to be mounted as indicated, except for those whose line contains the noauto keyword. Adding the -F option will
              make mount fork, so that the filesystems are mounted 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 filesystems in the file /etc/mtab.  If no arguments are given
              to mount, this list is printed.

              The mount program does not read the /etc/fstab file if device (or LABEL/UUID) and dir are specified. For example:

                     mount /dev/foo /dir

              If you want to override mount options from /etc/fstab you have to use:

                     mount device|dir -o <options>

              and  then  the  mount options from command line will be appended to the list of options from /etc/fstab.  The usual behaviour is
              that the last option wins if there is more duplicated options.

              When the proc filesystem is mounted (say at /proc), the files /etc/mtab and /proc/mounts have very similar contents. The  former
              has  somewhat  more information, such as the mount options used, but is not necessarily up-to-date (cf. the -n option below). It
              is possible to replace /etc/mtab by a symbolic link to /proc/mounts, and especially when you have very large numbers  of  mounts
              things  will  be much faster with that symlink, but some information is lost that way, and in particular using the "user" option
              will fail.

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

              Thus, given a line

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

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

                     mount /dev/cdrom


                     mount /cd

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

       The bind mounts.
              Since Linux 2.4.0 it is possible to remount part of the file hierarchy somewhere else. The call is
                     mount --bind olddir newdir
              or 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). It's also
              possible to use the bind mount to create a mountpoint from a regular directory, for example:

                     mount --bind foo foo

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

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

                     mount --bind olddir newdir
                     mount -o remount,ro,bind olddir 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 that the olddir has to be a mountpoint.

       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  propagation
              abilities.   A  unbindable  mount  is  a  private  mount  which cannot be cloned through a bind operation. Detailed semantics is
              documented in Documentation/filesystems/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


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

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

              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 automounter.

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

              Note  that,  depending on the filesystem type, state and kernel behavior, the system may still write to the device. For example,
              Ext3 or ext4 will replay its journal if the filesystem is dirty. To prevent this kind of write access, you  may  want  to  mount
              ext3 or ext4 filesystem with "ro,noload" mount options or set the block device to read-only mode, see command blockdev(8).

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

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

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

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

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

              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
              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.

              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

              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

       -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


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

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

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


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

       Some  of  these  options  could be enabled or disabled by default in the system kernel. To check the current setting see the options in

       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 kernel defaults. See also the description for
              strictatime and reatime mount options.

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

       auto   Can be mounted with the -a option.

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

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

              A commonly used option for removable media is context=system_u:object_r: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 defcontext with each other, but neither can be used with context.

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

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

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

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

              For more details, see selinux(8)

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

       dev    Interpret character or block special devices on the filesystem.

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

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

              Do not update directory inode access times on this filesystem.

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

       exec   Permit execution of binaries.

       noexec Do not 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).

              Specifies an encryption algorithm to use.  Used in conjunction with the loop option.

              Specifies the key size to use for an encryption algorithm. Used in conjunction with the loop and encryption options.  nofail  Do
              not  report errors for this device if it does not exist.  iversion Every time the inode is modified, the i_version field will be

              Do not increment the i_version inode field.

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

       nomand Do not allow mandatory locks on this filesystem.

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

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

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

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

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

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

              Use the kernel's default behaviour for inode access time 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 suidperl(1) installed.)

       silent Turn on the silent flag.

       loud   Turn off the silent flag.

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

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

              The  remount  functionality  follows  the  standard  way 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.

       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).


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

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

Mount options for adfs

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

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

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

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

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

              Print an informational message for each successful mount.

              Prefix used before volume name, when following a link.

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

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

              Give explicitly the location of the root block.

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

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

Mount options for cifs

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

Mount options for coherent


Mount options for debugfs

       The debugfs filesystem is a pseudo filesystem, traditionally mounted on /sys/kernel/debug.  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 values. When nothing is specified, they will be  set  to
              the  UID  and GID of the creating process.  For example, if there is a tty group with GID 5, then gid=5 will cause newly created
              PTYs to belong to the tty group.

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

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

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

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


              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 specified.

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

Mount options for ext

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

Mount options for ext2

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

              Support POSIX Access Control Lists (or not).

              Set the behaviour for the statfs system call. The minixdf behaviour is to return in the  f_blocks  field  the  total  number  of
              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.)

              No checking is done at mount time. This is the default. This is fast.  It is wise to invoke e2fsck(8) every now and  then,  e.g.
              at boot time.

       debug  Print debugging info upon each (re)mount.

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

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

              These options are accepted but ignored.

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

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

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

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

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

Mount options for ext3

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

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

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

              When the external journal device's major/minor numbers have changed, this option allows the user  to  specify  the  new  journal
              location.  The journal device is identified through its new major/minor numbers encoded in devnum.

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

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

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

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

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

       barrier=0 / barrier=1
              This enables/disables barriers.  barrier=0 disables it, barrier=1 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 ext3 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.

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

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

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

Mount options for ext4

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

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

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

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

              Update the ext4 filesystem's journal to the current format.

       barrier=0 / barrier=1 / barrier / nobarrier
              This  enables/disables the use of write barriers in the jbd code.  barrier=0 disables, barrier=1 enables.  This also requires an
              IO stack which can support barriers, and if jbd gets an error on a barrier write, it will disable again with a  warning.   Write
              barriers  enforce proper on-disk ordering of journal commits, making volatile disk write caches safe to use, at some performance
              penalty.  If your disks are battery-backed in one way or another, disabling barriers may safely improve performance.  The  mount
              options "barrier" and "nobarrier" can also be used to enable or disable barriers, for consistency with other ext4 mount options.

              The ext4 filesystem enables write barriers by default.

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

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

              Deferring block allocation until write-out time.

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

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

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

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

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

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

              fd = open("")/write(fd,..)/close(fd)/ rename("", "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  committed.   This  provides  roughly  the  same  level  of
              guarantees  as  ext3,  and  avoids the "zero-length" problem that can happen when a system crashes before the delayed allocation
              blocks are forced to disk.

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

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

       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.

              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

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

              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.)

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

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

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

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

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

              This option controls the permission check of mtime/atime.

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

              2      Other users can change timestamp.

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

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

              Three different levels of pickyness can be chosen:

                     Upper  and  lower  case  are  accepted  and  equivalent, long name parts are truncated (e.g.  verylongname.foobar becomes
           , leading and embedded spaces are accepted in each name part (name and extension).

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

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

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

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

              binary no translation is performed.  This is the default.

              text   CRLF<-->NL translation is performed on all files.

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

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

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

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

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

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

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

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

       tz=UTC This  option  disables  the  conversion  of  timestamps between local time (as used by Windows on FAT) and UTC (which Linux uses
              internally).  This is particularly useful when mounting devices (like digital cameras) that are set to UTC in order to avoid the
              pitfalls of local time.

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

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

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

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

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

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

Mount options for hfs

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

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

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

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

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

       quiet  Don't complain about invalid mount options.

Mount options for hpfs

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

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

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

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

              Do not abort mounting when certain consistency checks fail.

Mount options for iso9660

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              Session begins from sector xxx. (Since 2.3.4.)

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

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

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

Mount options for jfs

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

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

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

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

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

              These options are accepted but ignored.

Mount options for minix


Mount options for msdos

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

Mount options for ncpfs

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

Mount options for nfs and nfs4

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

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

Mount options for ntfs

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

              New name for the option earlier called iocharset.

       utf8   Use UTF-8 for converting file names.

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

              If enabled (posix=1), the filesystem distinguishes between upper and lower case. The 8.3 alias names are presented as hard links
              instead of being suppressed. This option is obsolete.

       uid=value, gid=value and umask=value
              Set the file permission on the filesystem.  The umask value is given in octal.  By default, the files are owned by root and  not
              readable by somebody else.

Mount options for proc

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       barrier=none / barrier=flush
              This 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


Mount options for squashfs


Mount options for smbfs

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

Mount options for sysv


Mount options for tmpfs

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

              The same as size, but in blocks of PAGE_CACHE_SIZE

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

       The  tmpfs  mount  options for sizing ( size, nr_blocks, and nr_inodes) accept a suffix k, m or g for Ki, Mi, Gi (binary kilo, 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.

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

                     prefers to allocate memory from the local node

                     prefers to allocate memory from the given Node

                     allocates memory only from nodes in NodeList

                     prefers to allocate from each node in turn

                     allocates from each node of NodeList in turn.

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

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

Mount options for ubifs

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

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

              ubiY   UBI device number 0, volume number Y

                     UBI device number X, volume with name NAME

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

       The following mount options are available:

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

              Do not bulk-read. This is the default.

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

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

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

Mount options for udf

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

       gid=   Set the default group.

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

       uid=   Set the default user.

       unhide Show otherwise hidden files.

              Show deleted files in lists.

              Unset strict conformance.

              Set the NLS character set.

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

       novrs  Skip volume sequence recognition.

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

              Override standard anchor location. Default: 256.

              Override the VolumeDesc location. (unused)

              Override the PartitionDesc location. (unused)

              Set the last block of the filesystem.

              Override the fileset block location. (unused)

              Override the root directory location. (unused)

Mount options for ufs

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

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

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

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

              5xbsd  Synonym for ufs2.

              sun    For filesystems created by SunOS or Solaris on Sparc.

              sunx86 For filesystems created by Solaris on x86.

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

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

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

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

              Set behaviour on error:

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

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

Mount options for umsdos

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

Mount options for vfat

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

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

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

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

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


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

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

              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. This mode is the default since
                     Linux 2.6.32.

Mount options for usbfs

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

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

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

Mount options for xenix


Mount options for xfs

              Sets the buffered I/O end-of-file preallocation size when doing delayed allocation writeout  (default  size  is  64KiB).   Valid
              values for this option are page size (typically 4KiB) through to 1GiB, inclusive, in power-of-2 increments.

              The  options enable/disable (default is enabled) 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 (by setting  or  removing  extended  attributes)  the  on-disk
              superblock feature bit field will be updated to reflect this format being in use.

              Enables  the  use  of  block  layer write barriers for writes into the journal and unwritten extent conversion.  This allows for
              drive level write caching to be enabled, for devices that support write barriers.

       dmapi  Enable the DMAPI (Data Management API) event callouts.  Use with the mtpt option.

       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.

              Sets the number of hash buckets available for hashing the in-memory inodes of the specified mount point.  If a value of zero  is
              used, the value selected by the default algorithm will be displayed in /proc/mounts.

              When  inode  clusters are emptied of inodes, keep them around on the disk (ikeep) - this is the traditional XFS behaviour and is
              still the default for now.  Using the noikeep option, inode clusters are returned to the free space pool.

              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.  This is provided for backwards compatibility, but causes problems for
              backup applications that cannot handle large inode numbers.

              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.  If largeio is specified, a filesystem that has a swidth specified will
              return the swidth value (in bytes) in st_blksize. If the filesystem does not  have  a  swidth  specified  but  does  specify  an
              allocsize  then  allocsize  (in bytes) will be returned instead.  If neither of these two options are specified, then filesystem
              will behave as if nolargeio was specified.

              Set the number of in-memory log buffers.  Valid numbers range from 2-8 inclusive.  The default value is 8 buffers for any recent

              Set  the size of each in-memory log buffer.  Size may be specified in bytes, or in kilobytes with a "k" suffix.  Valid sizes for
              version 1 and version 2 logs are 16384 (16k) and 32768 (32k).  Valid sizes for version 2 logs also include 65536  (64k),  131072
              (128k) and 262144 (256k).  The default value for any recent kernel is 32768.

       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.  Refer to xfs(5).

              Use  with  the  dmapi  option. The value specified here will be included in the DMAPI mount event, and should be the path of the
              actual mountpoint that is used.

              Data allocations will not be aligned at stripe unit boundaries.

              Access timestamps are not updated when a file is read.

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

       nouuid Don't check for double mounted filesystems using the filesystem uuid.  This is useful to mount LVM snapshot volumes.

              Make O_SYNC writes implement true O_SYNC.  WITHOUT this option, Linux XFS behaves as if an osyncisdsync option  is  used,  which
              will  make writes to files opened with the O_SYNC flag set behave as if the O_DSYNC flag had been used instead.  This can result
              in better performance without compromising data safety.  However if this option is not in effect, timestamp updates from  O_SYNC
              writes can be lost if the system crashes.  If timestamp updates are critical, use the osyncisosync option.

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

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

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

       sunit=value and swidth=value
              Used  to  specify  the  stripe  unit  and width for a RAID device or a stripe volume.  value must be specified in 512-byte block
              units.  If this option is not specified and the filesystem was made on a  stripe  volume  or  the  stripe  width  or  unit  were
              specified  for  the  RAID  device  at  mkfs  time,  then  the mount system call will restore the value from the superblock.  For
              filesystems that are made directly on RAID devices, these options can be used to override the information in the  superblock  if
              the underlying disk layout changes after the filesystem has been created.  The swidth option is required if the sunit option has
              been specified, and must be a multiple of the sunit value.

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

Mount options for xiafs

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


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

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

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

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

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

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

              mount /tmp/disk.img /mnt

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

       This type of mount knows about four options, namely loop, offset, sizelimit and encryption, that are really options to losetup(8).   If
       the  mount  requires  a  passphrase,  you  will  be prompted for one unless you specify a file descriptor to read from instead with the
       --pass-fd option.  (These options can be used in addition to those specific to the filesystem type.)

       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`.


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

       0      success

       1      incorrect invocation or permissions

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

       4      internal mount bug

       8      user interrupt

       16     problems writing or locking /etc/mtab

       32     mount failure

       64     some mount succeeded


       The syntax of external mount helpers is:

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

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


       /etc/fstab        filesystem table

       /etc/mtab         table of mounted filesystems

       /etc/mtab~        lock file

       /etc/mtab.tmp     temporary file

       /etc/filesystems  a list of filesystem types to try


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


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

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

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

       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

       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.


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


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

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