Provided by: mount_2.33.1-0.1ubuntu2_amd64 bug

NAME

       mount - mount a filesystem

SYNOPSIS

       mount [-l|-h|-V]

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

       mount [-fnrsvw] [-o options] device|dir

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

DESCRIPTION

       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 filesystem is used to control how data is
       stored on the device or provided in a virtual way by network or another services.

       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 option -t type is optional.  The mount command is usually able  to
       detect a filesystem.  The root permissions are necessary to mount a filesystem by default.
       See section "Non-superuser mounts" below for more details.  The previous contents (if any)
       and  owner  and  mode  of  dir  become  invisible,  and as long as this filesystem remains
       mounted, the pathname dir refers to the root of the filesystem on device.

       If only the directory or the device is given, for example:

              mount /dir

       then mount looks for a mountpoint (and if not found then for a device) in  the  /etc/fstab
       file.   It's  possible  to  use  the  --target  or  --source  options  to avoid ambivalent
       interpretation of the given argument.  For example:

              mount --target /mountpoint

       The same filesystem may be mounted more than  once,  and  in  some  cases  (e.g.   network
       filesystems)  the  same filesystem maybe be mounted on the same mountpoint more times. The
       mount command does not implement any policy to control  this  behavior.  All  behavior  is
       controlled  by  kernel  and  it is usually specific to filesystem driver. The exception is
       --all, in this case already mounted filesystems are ignored  (see  --all  below  for  more
       details).

   Listing the mounts
       The listing mode is maintained for backward compatibility only.

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

       The following command lists all mounted filesystems (of type type):

              mount [-l] [-t type]

       The option -l adds labels to this listing.  See below.

   Indicating the device and filesystem
       Most devices are indicated by a filename (of a block special device), like /dev/sda1,  but
       there  are other possibilities.  For example, in the case of an NFS mount, device may look
       like knuth.cwi.nl:/dir.  It is also possible to indicate a block special device using  its
       filesystem  label  or  UUID  (see  the -L and -U options below), or its partition label or
       UUID.  Partition identifiers are supported for example for GUID Partition Tables (GPT).

       The device name of disk partitions  are  unstable;  hardware  reconfiguration,  adding  or
       removing  a device can cause change in names. This is reason why it's strongly recommended
       to use filesystem or partition identificators like UUID or LABEL.

       The command lsblk --fs provides overview of filesystems, LABELs  and  UUIDs  on  available
       block  devices.   The command blkid -p <device> provides details about a filesystem on the
       specified device.

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

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

       Note that mount(8) uses UUIDs as strings.   The  UUIDs  from  the  command  line  or  from
       fstab(5)  are  not converted to internal binary representation.  The string 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  already  mounted'  from
       mount can be confusing.)

   The files /etc/fstab, /etc/mtab and /proc/mounts
       The  file /etc/fstab (see fstab(5)), may contain lines describing what devices are usually
       mounted where, using which options.  The default location of  the  fstab(5)  file  can  be
       overridden with the --fstab path command-line option (see below for more details).

       The command

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

       (usually  given  in a bootscript) causes all filesystems mentioned in fstab (of the proper
       type and/or having or not having the proper options) to be mounted  as  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  specify  on  the
       command line only the device, or only the mount point.

       The  programs  mount  and  umount  traditionally  maintained  a  list of currently mounted
       filesystems in  the  file  /etc/mtab.   The  support  for  regular  classic  /etc/mtab  is
       completely  disabled  in  compile  time by default, because on current Linux systems it is
       better to make it a symlink to /proc/mounts instead. The regular mtab file  maintained  in
       userspace  cannot  reliably  work  with  namespaces,  containers  and other advanced Linux
       features.  If the regular mtab support is enabled than it's possible to use  the  file  as
       well as the symlink.

       If no arguments are given to mount, the list of mounted filesystems is printed.

       If you want to override mount options from /etc/fstab you have to use the -o option:

              mount device|dir -o options

       and  then  the mount options from the command line will be appended to the list of options
       from /etc/fstab.  This default behaviour is possible to  change  by  command  line  option
       --options-mode.   The usual behavior is that the last option wins if there are conflicting
       ones.

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

              mount /dev/foo /dir

       This default behaviour is possible to change by command line option --options-source-force
       to always read configuration from fstab.  For  non-root  users  mount  always  read  fstab
       configuration.

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

       Thus, given a line

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

       any user can mount the iso9660 filesystem found on an inserted CDROM using the command:
              mount /cd

       Note that mount is very strict about non-root users and all  paths  specified  on  command
       line  are  verified  before fstab is parsed or a helper program is executed. It's strongly
       recommended to use a valid mountpoint to specify filesystem, otherwise mount may fail. For
       example it's bad idea to use NFS or CIFS source on command line.

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

   Bind mount operation
       Remount part of the file hierarchy somewhere else.  The call is:

              mount --bind olddir newdir

       or by using this fstab entry:

              /olddir /newdir none bind

       After this call the same contents are accessible in two places.

       It is important to understand that "bind" does not to create any second-class  or  special
       node in the kernel VFS. The "bind" is just another operation to attach a filesystem. There
       is nowhere stored information that the filesystem has been attached by  "bind"  operation.
       The olddir and newdir are independent and the olddir maybe be umounted.

       One can also remount a single file (on a single file).  It's also possible to use the bind
       mount to create a mountpoint from a regular directory, for example:

              mount --bind foo foo

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

              mount --rbind olddir newdir

       Note  that the filesystem mount options maintained by kernel will remain the same as those
       on the original mount point.  The userspace mount  options  (e.g.  _netdev)  will  not  be
       copied  by  mount(8)  and  it's  necessary explicitly specify the options on mount command
       line.

       mount(8) since v2.27 allows to change the mount options by passing  the  relevant  options
       along with --bind.  For example:

              mount -o bind,ro foo foo

       This  feature  is  not supported by the Linux kernel; it is implemented in userspace by an
       additional mount(2) remounting system call.  This solution is not atomic.

       The alternative (classic) way to create a read-only bind  mount  is  to  use  the  remount
       operation, for example:

              mount --bind olddir newdir
              mount -o remount,bind,ro olddir newdir

       Note  that  a  read-only  bind  will  create  a  read-only mountpoint (VFS entry), but the
       original filesystem superblock will still be writable, meaning that  the  olddir  will  be
       writable, but the newdir will be read-only.

       It's  also  possible to change nosuid, nodev, noexec, noatime, nodiratime and relatime VFS
       entry flags by "remount,bind" operation.  The another  (for  example  filesystem  specific
       flags)  are  silently  ignored.   It's impossible to change mount options recursively (for
       example with -o rbind,ro).

       mount(8) since v2.31 ignores the bind flag from /etc/fstab on remount  operation  (if  "-o
       remount"  specified  on command line). This is necessary to fully control mount options on
       remount by command line. In the previous versions the bind flag has  been  always  applied
       and  it  was  impossible  to  re-define  mount  options  without interaction with the bind
       semantic. This mount(8)  behavior  does  not  affect  situations  when  "remount,bind"  is
       specified in the /etc/fstab file.

   The move operation
       Move a mounted tree to another place (atomically).  The call is:

              mount --move olddir newdir

       This  will  cause the contents which previously appeared under olddir to now be accessible
       under newdir.  The physical location of the files is not changed.  Note that olddir has to
       be a mountpoint.

       Note  also  that  moving a mount residing under a shared mount is invalid and unsupported.
       Use findmnt -o TARGET,PROPAGATION to see the current propagation flags.

   Shared subtree 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 the ability to create mirrors of that mount
       such that mounts and unmounts within any of the mirrors propagate to the other mirror.   A
       slave  mount  receives  propagation  from its master, but not vice versa.  A private mount
       carries no propagation abilities.  An unbindable mount is a private mount which cannot  be
       cloned   through   a   bind   operation.    The   detailed  semantics  are  documented  in
       Documentation/filesystems/sharedsubtree.txt file in the kernel source tree.

       Supported operations are:

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

       The following commands allow one to recursively change the type of all the mounts under  a
       given mountpoint.

              mount --make-rshared mountpoint
              mount --make-rslave mountpoint
              mount --make-rprivate mountpoint
              mount --make-runbindable mountpoint

       mount(8)  does  not  read  fstab(5) when a --make-* operation is requested.  All necessary
       information has to be specified on the command line.

       Note that the Linux kernel does not allow to change  multiple  propagation  flags  with  a
       single  mount(2)  system  call, and the flags cannot be mixed with other mount options and
       operations.

       Since util-linux 2.23 the mount command allows to do more propagation  (topology)  changes
       by one mount(8) call and do it also together with other mount operations.  This feature is
       EXPERIMENTAL.  The propagation flags are applied by additional mount(2) system calls  when
       the  preceding  mount  operations were successful.  Note that this use case is not atomic.
       It is possible to specify the propagation flags in fstab(5)  as  mount  options  (private,
       slave, shared, unbindable, rprivate, rslave, rshared, runbindable).

       For example:

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

       is the same as:

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

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.

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

       Command-line options available for the mount command are:

       -a, --all
              Mount all filesystems (of the given types) mentioned in  fstab  (except  for  those
              whose  line  contains  the  noauto keyword).  The filesystems are mounted following
              their order in fstab.  The mount command compares filesystem source, target (and fs
              root  for  bind  mount  or btrfs) to detect already mounted filesystems. The kernel
              table with already mounted filesystems is cached during mount --all. It means  that
              all duplicated fstab entries will be mounted.

              Note  that it is a bad practice to use mount -a for fstab checking. The recommended
              solution is findmnt --verify.

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

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

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

       -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 an existing record in /etc/mtab and fails when
              the record already exists (with a regular non-fake mount, this check is done by the
              kernel).

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

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

       -l, --show-labels
              Add  the  labels  in the mount output.  mount must have permission to read the disk
              device (e.g. be set-user-ID 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).

       -M, --move
              Move a subtree to some other place.  See above, the subsection The move operation.

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

       -N, --namespace ns
              Perform mount in namespace specified by ns.  ns is either PID of process running in
              that namespace or special file representing that namespace.

              mount(8) switches to the namespace when it reads /etc/fstab, writes  /etc/mtab  (or
              writes  to  /run/mount)  and  calls  mount(2) system call, otherwise it runs in the
              original namespace. It means that the target namespace does not have to contain any
              libraries or another requirements necessary to execute mount(2) command.

              See namespaces(7) for more information.

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

                     mount -a -O no_netdev

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

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

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

                     mount -a -t ext2 -O _netdev

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

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

                     mount LABEL=mydisk -o noatime,nodev,nosuid

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

       --options-mode mode
              Controls  how  to  combine  options from fstab/mtab with options from command line.
              mode can be one of ignore, append, prepend or replace.  For  example  append  means
              that  options  from fstab are appended to options from command line.  Default value
              is prepend -- it means command line options  are  evaluated  after  fstab  options.
              Note that the last option wins if there are conflicting ones.

       --options-source source
              Source  of  default  options.   source  is  comma separated list of fstab, mtab and
              disable.  disable disables fstab  and  mtab  and  disables  --options-source-force.
              Default value is fstab,mtab.

       --options-source-force
              Use options from fstab/mtab even if both device and dir are specified.

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

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

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

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

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

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

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

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

       -t, --types fstype
              The  argument  following  the  -t  is  used  to  indicate the filesystem type.  The
              filesystem types which are currently supported depend on the running  kernel.   See
              /proc/filesystems and /lib/modules/$(uname -r)/kernel/fs for a complete list of the
              filesystems.  The most common are ext2, ext3, ext4, xfs, btrfs, vfat, sysfs,  proc,
              nfs and cifs.

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

              If no -t option is given, or if the auto type is specified, mount will try to guess
              the  desired  type.  Mount uses the blkid library for guessing the filesystem type;
              if that does not turn up anything that looks familiar, mount will try to  read  the
              file  /etc/filesystems,  or, if that does not exist, /proc/filesystems.  All of the
              filesystem types listed there will be tried, except  for  those  that  are  labeled
              "nodev"  (e.g.  devpts,  proc  and nfs).  If /etc/filesystems ends in a line with a
              single  *,  mount  will  read  /proc/filesystems  afterwards.   While  trying,  all
              filesystem types will be mounted with the mount option silent.

              The   auto  type  may  be  useful  for  user-mounted  floppies.   Creating  a  file
              /etc/filesystems can be useful to change the probe order (e.g., to try vfat  before
              msdos or ext3 before ext2) or if you use a kernel module autoloader.

              More  than  one  type  may be specified in a comma-separated list, for option -t as
              well as in an /etc/fstab entry.  The list of filesystem types for option -t can  be
              prefixed  with  no  to  specify  the  filesystem types on which no action should be
              taken.  The prefix no has no effect when specified in an /etc/fstab entry.

              The prefix no can be meaningful with the -a option.  For example, the command

                     mount -a -t nomsdos,smbfs

              mounts all filesystems except those of type msdos and smbfs.

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

       -U, --uuid uuid
              Mount the partition that has the specified uuid.

       -v, --verbose
              Verbose mode.

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

              Note  that  specify  -w on command line forces mount command to never try read-only
              mount on write-protected devices. The default is  try  read-only  if  the  previous
              mount syscall with read-write flags failed.

       -V, --version
              Display version information and exit.

       -h, --help
              Display help text and exit.

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 an effect only for ext2,
       ext3, ext4, fat, vfat and ufs):

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

       atime  Do  not  use  the noatime feature, so the inode access time is controlled by kernel
              defaults.  See also the descriptions of the relatime and strictatime 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).  This works for all inode types (directories
              too), so it implies nodiratime.

       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 or ext4 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 becomes visible to userspace.  This was found to be
              useful for things like stateless linux.

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

              Warning: the context value might contain commas, in which case the value has to  be
              properly quoted, otherwise mount(8) will interpret the comma as a separator between
              mount options.  Don't forget that the shell  strips  off  quotes  and  thus  double
              quoting is required.  For example:

                     mount -t tmpfs none /mnt -o \
                       'context="system_u:object_r:tmp_t:s0:c127,c456",noexec'

              For more details, see selinux(8).

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

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

       dev    Interpret character or block special devices on the filesystem.

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

       diratime
              Update directory inode access times on  this  filesystem.   This  is  the  default.
              (This option is ignored when noatime is set.)

       nodiratime
              Do  not  update  directory  inode access times on this filesystem.  (This option is
              implied when noatime is set.)

       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 permit direct execution of any binaries on the mounted filesystem.

       group  Allow an ordinary user to mount the filesystem if one of that user's 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 network 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 it doesn't break mutt or  other  applications  that
              need to know if a file has been read since the last time it was modified.)

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

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

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

       nostrictatime
              Use the kernel's default behavior for inode access time updates.

       lazytime
              Only update times (atime, mtime, ctime) on the in-memory version of the file inode.

              This mount option significantly reduces writes to the  inode  table  for  workloads
              that perform frequent random writes to preallocated files.

              The on-disk timestamps are updated only when:

              - the inode needs to be updated for some change unrelated to file timestamps

              - the application employs fsync(2), syncfs(2), or sync(2)

              - an undeleted inode is evicted from memory

              - more than 24 hours have passed since the i-node was written to disk.

       nolazytime
              Do not use the lazytime feature.

       suid   Allow set-user-ID or set-group-ID bits to take effect.

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

       silent Turn on the silent flag.

       loud   Turn off the silent flag.

       owner  Allow  an  ordinary  user  to mount the filesystem if that user 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
              writable.  It does not change device or mount point.

              The  remount operation together with the bind flag has special semantic. See above,
              the subsection Bind mounts.

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

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

              After this call all old mount options are replaced and arbitrary stuff  from  fstab
              (or  mtab)  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 and merges these options with the  options  from
              the  command  line  (-o).   If no mountpoint is found in fstab, then a remount with
              unspecified source is allowed.

       ro     Mount the filesystem read-only.

       rw     Mount the filesystem read-write.

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

       user   Allow an ordinary user to mount the filesystem.  The name of the mounting  user  is
              written  to the mtab file (or to the private libmount file in /run/mount on systems
              without a regular mtab) so that this same user 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 user to mount the filesystem.  This is the default; it does  not
              imply any other options.

       users  Allow  any  user  to  mount  and  to  unmount  the filesystem, even when some other
              ordinary user mounted it.  This option implies  the  options  noexec,  nosuid,  and
              nodev   (unless   overridden   by   subsequent  options,  as  in  the  option  line
              users,exec,dev,suid).

       X-*    All options prefixed  with  "X-"  are  interpreted  as  comments  or  as  userspace
              application-specific options.  These options are not stored in the user space (e.g.
              mtab file), nor sent to the mount.type helpers nor to  the  mount(2)  system  call.
              The suggested format is X-appname.option.

       x-*    The  same  as  X-*  options, but stored permanently in the user space. It means the
              options are also available for umount or another operations.   Note  that  maintain
              mount  options  in  user space is tricky, because it's necessary use libmount based
              tools and there is no guarantee that the options  will  be  always  available  (for
              example after a move mount operation or in unshared namespace).

              Note  that  before  util-linux  v2.30  the  x-* options have not been maintained by
              libmount and stored in user space (functionality was the same as have X-* now), but
              due to growing number of use-cases (in initrd, systemd etc.) the functionality have
              been extended to keep existing fstab configurations usable without a change.

       X-mount.mkdir[=mode]
              Allow to  make  a  target  directory  (mountpoint).   The  optional  argument  mode
              specifies  the  filesystem  access  mode  used for mkdir(2) in octal notation.  The
              default mode is 0755.  This functionality is supported only for  root  users.   The
              option  is  also  supported  as  x-mount.mkdir,  this  notation  is  deprecated for
              mount.mkdir since v2.30.

FILESYSTEM-SPECIFIC MOUNT OPTIONS

       You should consult the respective man page for the filesystem first.  If you want to  know
       what  options  the  ext4  filesystem  supports,  then check the ext4(5) man page.  If that
       doesn't exist, you can also check the corresponding mount page like  mount.cifs(8).   Note
       that you might have to install the respective userland tools.

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

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

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

       ownmask=value and othmask=value
              Set  the  permission  mask  for  ADFS  'owner' permissions and 'other' permissions,
              respectively    (default:    0700    and    0077,    respectively).     See    also
              /usr/src/linux/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 permissions.
              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 debugfs
       The debugfs filesystem is a pseudo filesystem, traditionally mounted on /sys/kernel/debug.
       As of kernel version 3.4, debugfs has the following options:

       uid=n, gid=n
              Set the owner and group of the mountpoint.

       mode=value
              Sets the mode of the mountpoint.

   Mount options for devpts
       The devpts filesystem is a pseudo filesystem, traditionally mounted on /dev/pts.  In order
       to acquire a pseudo terminal, a process opens /dev/ptmx; the number of the pseudo terminal
       is then made available to the process and the pseudo terminal slave  can  be  accessed  as
       /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.

       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 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 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  current
              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 inflexible.  With this option you can relax it.

       check=value
              Three different levels of pickiness 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 extension).

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

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

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

       conv=mode
              This option is obsolete and may fail or being ignored.

       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 parameters will
              be  printed  (these  data  are  also  printed  if  the  parameters  appear  to   be
              inconsistent).

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

       dos1xfloppy
              If set, use a fallback default BIOS Parameter Block  configuration,  determined  by
              backing device size.  These static parameters match defaults assumed by DOS 1.x for
              160 kiB, 180 kiB, 320 kiB, and 360 kiB floppies and floppy images.

       errors={panic|continue|remount-ro}
              Specify FAT behavior on critical errors: panic, continue without doing anything, or
              remount the partition in read-only mode (default behavior).

       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  Unicode
              characters.   The  default  is  iso8859-1.   Long  filenames  are stored on disk in
              Unicode format.

       nfs={stale_rw|nostale_ro}
              Enable this only if you want to export the FAT filesystem over NFS.

              stale_rw: This option maintains an index (cache) of directory inodes which is  used
              by  the  nfs-related  code  to improve look-ups.  Full file operations (read/write)
              over NFS are supported but with cache eviction at NFS server, this could result  in
              spurious ESTALE errors.

              nostale_ro:  This  option  bases  the  inode  number and file handle on the on-disk
              location of a file in the FAT directory entry.  This ensures that ESTALE  will  not
              be  returned  after a file is evicted from the inode cache.  However, it means that
              operations such as  rename,  create  and  unlink  could  cause  file  handles  that
              previously  pointed  at  one file to point at a different file, potentially causing
              data corruption.  For this reason, this option also mounts the filesystem readonly.

              To maintain backward compatibility,  '-o  nfs'  is  also  accepted,  defaulting  to
              stale_rw.

       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.

       time_offset=minutes
              Set offset for conversion of timestamps from local time used by FAT to UTC.   I.e.,
              minutes will be subtracted from each timestamp to convert it to UTC used internally
              by Linux.  This is useful when the time zone set in the kernel via  settimeofday(2)
              is  not the time zone used by the filesystem.  Note that this option still does not
              provide correct time stamps in all cases in presence of DST  -  time  stamps  in  a
              different DST setting will be off by one hour.

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

       rodir  FAT has the  ATTR_RO  (read-only)  attribute.   On  Windows,  the  ATTR_RO  of  the
              directory  will  just  be ignored, and is used only by applications as a flag (e.g.
              it's set for the customized folder).

              If you want to use ATTR_RO as read-only flag  even  for  the  directory,  set  this
              option.

       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  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 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  current
              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=mode
              This option is obsolete and may fail or being ignored.

       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 an 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.

       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 and
              execute permission for everybody.)  Octal mode values require 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.)

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

       conv=mode
              This option is obsolete and may fail or being ignored.

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

       session=x
              Select number of session on multisession CD.

       sbsector=xxx
              Session begins from sector xxx.

       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 ends.

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

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

   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 ntfs
       iocharset=name
              Character set to use when returning file names.  Unlike VFAT, NTFS suppresses names
              that contain nonconvertible 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 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 overlay
       Since Linux 3.18 the  overlay  pseudo  filesystem  implements  a  union  mount  for  other
       filesystems.

       An  overlay  filesystem  combines  two  filesystems  -  an  upper  filesystem  and a lower
       filesystem.  When a name exists in both filesystems, the object in the upper filesystem is
       visible  while  the  object  in  the  lower filesystem is either hidden or, in the case of
       directories, merged with the upper object.

       The lower filesystem can be any filesystem supported by Linux and  does  not  need  to  be
       writable.   The lower filesystem can even be another overlayfs.  The upper filesystem will
       normally be writable and if it is it must  support  the  creation  of  trusted.*  extended
       attributes, and must provide a valid d_type in readdir responses, so NFS is not suitable.

       A read-only overlay of two read-only filesystems may use any filesystem type.  The options
       lowerdir and upperdir are combined into a merged directory by using:

              mount -t overlay  overlay  \
                -olowerdir=/lower,upperdir=/upper,workdir=/work  /merged

       lowerdir=directory
              Any filesystem, does not need to be on a writable filesystem.

       upperdir=directory
              The upperdir is normally on a writable filesystem.

       workdir=directory
              The workdir needs to be an empty directory on the same filesystem as upperdir.

   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 directories.

              rupasov
                     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.

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

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

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

   Mount options for ubifs
       UBIFS  is  a  flash  filesystem 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 OSTA, the Optical Storage
       Technology Association, and is often used for DVD-ROM, frequently in the form of a  hybrid
       UDF/ISO-9660  filesystem. It is, however, perfectly usable by itself on disk drives, flash
       drives and other block devices.  See also iso9660.

       uid=   Make all files in the filesystem belong to  the  given  user.   uid=forget  can  be
              specified  independently  of  (or usually in addition to) uid=<user> and results in
              UDF not storing uids to the media. In fact the recorded uid is the 32-bit  overflow
              uid  -1  as defined by the UDF standard.  The value is given as either <user> which
              is a valid user name or the corresponding decimal user id, or  the  special  string
              "forget".

       gid=   Make  all  files  in  the  filesystem belong to the given group.  gid=forget can be
              specified independently of (or usually in addition to) gid=<group> and  results  in
              UDF  not storing gids to the media. In fact the recorded gid is the 32-bit overflow
              gid -1 as defined by the UDF standard.  The value is given as either <group>  which
              is  a valid group name or the corresponding decimal group id, or the special string
              "forget".

       umask= Mask out the given permissions from all inodes read from the filesystem.  The value
              is given in octal.

       mode=  If  mode=  is  set  the  permissions  of  all  non-directory  inodes  read from the
              filesystem will be set to the given mode. The value is given in octal.

       dmode= If dmode= is set the permissions of all directory inodes read from  the  filesystem
              will be set to the given dmode. The value is given in octal.

       bs=    Set  the  block  size. Default value prior to kernel version 2.6.30 was 2048. Since
              2.6.30 and prior to 4.11 it was logical device block size with  fallback  to  2048.
              Since  4.11  it is logical block size with fallback to any valid block size between
              logical device block size and 4096.

              For other details see the mkudffs(8) 2.0+ manpage, sections COMPATIBILITY and BLOCK
              SIZE.

       unhide Show otherwise hidden files.

       undelete
              Show deleted files in lists.

       adinicb
              Embed data in the inode. (default)

       noadinicb
              Don't embed data in the inode.

       shortad
              Use short UDF address descriptors.

       longad Use long UDF address descriptors. (default)

       nostrict
              Unset strict conformance.

       iocharset=
              Set  the  NLS  character  set.  This  requires  kernel compiled with CONFIG_UDF_NLS
              option.

       utf8   Set the UTF-8 character set.

   Mount options for debugging and disaster recovery
       novrs  Ignore the Volume Recognition Sequence and attempt to mount anyway.

       session=
              Select the session number for multi-session recorded optical media. (default=  last
              session)

       anchor=
              Override standard anchor location. (default= 256)

       lastblock=
              Set the last block of the filesystem.

   Unused historical mount options that may be encountered and should be removed
       uid=ignore
              Ignored, use uid=<user> instead.

       gid=ignore
              Ignored, use gid=<group> instead.

       volume=
              Unimplemented and ignored.

       partition=
              Unimplemented and ignored.

       fileset=
              Unimplemented and ignored.

       rootdir=
              Unimplemented and ignored.

   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).

              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.

              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 behavior 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 possible.  The  escape  character
              is ':' because it is otherwise invalid on the vfat filesystem.  The escape sequence
              that gets used, where u is the Unicode character, is: ':', (u &  0x3f),  ((u>>6)  &
              0x3f), (u>>12).

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

       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 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.

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

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

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

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

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

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

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

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

THE LOOP DEVICE

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

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

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

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

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

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

              mount /tmp/disk.img /mnt

              mount -t ext4 /tmp/disk.img /mnt

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

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

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

       Since util-linux v2.29 mount command re-uses the loop device rather than initialize a  new
       device  if the same backing file is already used for some loop device with the same offset
       and sizelimit. This is necessary to avoid a filesystem corruption.

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

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

EXTERNAL HELPERS

       The syntax of external mount helpers is:

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

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

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

FILES

       See also "The files /etc/fstab, /etc/mtab and /proc/mounts" section above.

       /etc/fstab        filesystem table

       /run/mount        libmount private runtime directory

       /etc/mtab         table of mounted filesystems or symlink to /proc/mounts

       /etc/mtab~        lock file (unused on systems with mtab symlink)

       /etc/mtab.tmp     temporary file (unused on systems with mtab symlink)

       /etc/filesystems  a list of filesystem types to try

ENVIRONMENT

       LIBMOUNT_FSTAB=<path>
              overrides the default location of the fstab file (ignored for suid)

       LIBMOUNT_MTAB=<path>
              overrides the default location of the mtab file (ignored for suid)

       LIBMOUNT_DEBUG=all
              enables libmount debug output

       LIBBLKID_DEBUG=all
              enables libblkid debug output

       LOOPDEV_DEBUG=all
              enables loop device setup debug output

SEE ALSO

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

BUGS

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

       Some Linux filesystems don't support -o sync nor -o dirsync (the ext2, ext3, ext4, fat and
       vfat filesystems do support synchronous updates (a la BSD)  when  mounted  with  the  sync
       option).

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

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

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

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

HISTORY

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

AUTHORS

       Karel Zak <kzak@redhat.com>

AVAILABILITY

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