MOUNT(8)                      System Administration                     MOUNT(8)

       mount - mount a filesystem

       mount [-h|-V]

       mount [-l] [-t fstype]

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

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

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

       mount --bind|--rbind|--move olddir newdir


       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 other 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 ambiguous interpretation of the given argument. For

          mount --target /mountpoint

       The same filesystem may be mounted more than once, and in some cases
       (e.g., network filesystems) the same filesystem may be mounted on the
       same mountpoint multiple times. The mount command does not implement any
       policy to control this behavior. All behavior is controlled by the kernel
       and it is usually specific to the 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

       The device names of disk partitions are unstable; hardware
       reconfiguration, and adding or removing a device can cause changes in
       names. This is the reason why it’s strongly recommended to use filesystem
       or partition identifiers like UUID or LABEL. Currently supported
       identifiers (tags):

           Human readable filesystem identifier. See also -L.

           Filesystem universally unique identifier. The format of the UUID is
           usually a series of hex digits separated by hyphens. See also -U.

           Note that mount 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.

           Human readable partition identifier. This identifier is independent
           on filesystem and does not change by mkfs or mkswap operations It’s
           supported for example for GUID Partition Tables (GPT).

           Partition universally unique identifier. This identifier is
           independent on filesystem and does not change by mkfs or mkswap
           operations It’s supported for example for GUID Partition Tables

           Hardware block device ID as generated by udevd. This identifier is
           usually based on WWN (unique storage identifier) and assigned by the
           hardware manufacturer. See ls /dev/disk/by-id for more details, this
           directory and running udevd is required. This identifier is not
           recommended for generic use as the identifier is not strictly defined
           and it depends on udev, udev rules and hardware.

       The command lsblk --fs provides an 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,id,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).

       The proc filesystem is not associated with a special device, and when
       mounting it, an arbitrary keyword - for example, 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

   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 in parallel.

       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(8) traditionally maintained a list of
       currently mounted filesystems in the file /etc/mtab. The support for
       regular classic /etc/mtab is completely disabled at compile time by
       default, because on current Linux systems it is better to make /etc/mtab
       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, then
       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

       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 can be changed
       using the --options-mode command-line option. 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, ID, PARTUUID or PARTLABEL) and dir are specified. For
       example, to mount device foo at /dir:

          mount /dev/foo /dir

       This default behaviour can be changed by using the --options-source-force
       command-line option to always read configuration from fstab. For non-root
       users mount always reads the 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

       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 a bad
       idea to use NFS or CIFS source on command line.

       Since util-linux 2.35, mount does not exit when user permissions are
       inadequate according to libmount’s internal security rules. Instead, it
       drops suid permissions and continues as regular non-root user. This
       behavior supports use-cases where root permissions are not necessary
       (e.g., fuse filesystems, user namespaces, etc).

       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 a 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 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 a "bind" operation.
       The olddir and newdir are independent and the olddir may be unmounted.

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

          mount --bind foo foo

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

          mount --rbind olddir newdir

       Note that the filesystem mount options maintained by the 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 and it’s necessary to
       explicitly specify the options on the mount command line.

       Since util-linux 2.27 mount permits changing 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

       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

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

       Since util-linux 2.31, mount ignores the bind flag from /etc/fstab on a
       remount operation (if "-o remount" is specified on command line). This is
       necessary to fully control mount options on remount by command line. In
       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 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; see also mount_namespaces(7).

       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 changing 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 can be used to do more
       propagation (topology) changes by one mount(8) call and do it also
       together with other mount operations. 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 /foo
           mount --make-private /foo
           mount --make-unbindable /foo

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

       The mount command 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. This means
           that all duplicated fstab entries will be mounted.

           The option --all is possible to use for remount operation too. In
           this case all filters (-t and -O) are applied to the table of already
           mounted filesystems.

           Since version 2.35 is possible to use the command line option -o to
           alter mount options from fstab (see also --options-mode).

           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 the 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 does not pass this option to the /sbin/mount.type

       -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 proceed in parallel. A disadvantage is that
           the order of the mount operations is undefined. 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

       -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 the mount operation in the mount namespace specified by ns.
           ns is either PID of process running in that namespace or special file
           representing that namespace.

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

           See mount_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

       -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

       --options-mode mode
           Controls how to combine options from fstab/mtab with options from the
           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 the command line. The 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 a comma-separated list of fstab,
           mtab and disable. disable disables fstab and mtab and disables
           --options-source-force. The default value is fstab,mtab.

           Use options from fstab/mtab even if both device and dir are

       -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.

           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 the target (mountpoint) or source
           (device). This option allows you 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 the target (mountpoint) or source
           (device). This option allows you to explicitly define that the
           argument is the mount target.

       --target-prefix directory
           Prepend the specified directory to all mount targets. This option can
           be used to follow fstab, but mount operations are done in another
           place, for example:

           mount --all --target-prefix /chroot -o X-mount.mkdir

           mounts all from system fstab to /chroot, all missing mountpoint are
           created (due to X-mount.mkdir). See also --fstab to use an
           alternative fstab.

       -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 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(8) 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 '' 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 libblkid(3)
           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
           the -t option as well as in an /etc/fstab entry. The list of
           filesystem types for the -t option 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

           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. Read-write is the kernel default and
           the mount default is to try read-only if the previous mount syscall
           with read-write flags on write-protected devices of filesystems

           A synonym is -o rw.

           Note that specifying -w on the command line forces mount to never try
           read-only mount on write-protected devices or already mounted
           read-only filesystems.

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

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

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

       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 ext_N_

       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, ufs and xfs):

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

           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.

           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.

           Can be mounted with the -a option.

           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
           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

           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

           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 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

          mount -t tmpfs none /mnt -o \

       For more details, see selinux(8).

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

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

           Interpret character or block special devices on the filesystem.

           Do not interpret character or block special devices on the

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

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

           All directory updates within the filesystem should be done
           synchronously. This affects the following system calls: creat(2),
           link(2), unlink(2), symlink(2), mkdir(2), rmdir(2), mknod(2) and

           Permit execution of binaries.

           Do not permit direct execution of any binaries on the mounted

           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).

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

           Do not increment the i_version inode field.

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

           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).

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

           Update inode access times relative to modify or change time. Access
           time is only updated if the previous access time was earlier than the
           current modify or change time. (Similar to noatime, but it doesn’t
           break mutt(1) or other applications that need to know if a file has
           been read since the last time it was modified.)

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

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

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

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

           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

           •   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 inode was written to

           Do not use the lazytime feature.

           Honor set-user-ID and set-group-ID bits or file capabilities when
           executing programs from this filesystem.

           Do not honor set-user-ID and set-group-ID bits or file capabilities
           when executing programs from this filesystem. In addition, SELinux
           domain transitions require permission nosuid_transition, which in
           turn needs also policy capability nnp_nosuid_transition.

           Turn on the silent flag.

           Turn off the silent flag.

           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

           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

           The remount operation together with the bind flag has special
           semantics. 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.

           mount allows the use of --all to remount all already mounted
           filesystems which match a specified filter (-O and -t). For example:

           mount --all -o remount,ro -t vfat

           remounts all already mounted vfat filesystems in read-only mode. Each
           of the filesystems is remounted by mount -o remount,ro /dir semantic.
           This means the mount command reads fstab or mtab and merges these
           options with the options from the command line.

           Mount the filesystem read-only.

           Mount the filesystem read-write.

           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.

           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).

           Forbid an ordinary user to mount the filesystem. This is the default;
           it does not imply any other options.

           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).

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

           The same as X-* options, but stored permanently in user space. This
           means the options are also available for umount(8) or other
           operations. Note that maintaining 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 for X-* now), but due to the growing number of use-cases
           (in initrd, systemd etc.) the functionality has been extended to keep
           existing fstab configurations usable without a change.

           Allow to make a target directory (mountpoint) if it does not exit
           yet. 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 or when mount executed
           without suid permissions. The option is also supported as
           x-mount.mkdir, this notation is deprecated since v2.30.

           Do not follow symlinks when resolving paths. Symlinks can still be
           created, and readlink(1), readlink(2), realpath(1), and realpath(3)
           all still work properly.

       This section lists options that are specific to particular filesystems.
       Where possible, you should first consult filesystem-specific manual pages
       for details. Some of those pages are listed in the following table.

       │                 │               │
       │Filesystem(s)    Manual page   │
       │                 │               │
       │btrfs            │ btrfs(5)      │
       │                 │               │
       │cifs             │ mount.cifs(8) │
       │                 │               │
       │ext2, ext3, ext4 │ ext4(5)       │
       │                 │               │
       │fuse             │ fuse(8)       │
       │                 │               │
       │nfs              │ nfs(5)        │
       │                 │               │
       │tmpfs            │ tmpfs(5)      │
       │                 │               │
       │xfs              │ xfs(5)        │

       Note that some of the pages listed above might be available only after
       you install the respective userland tools.

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

       What options are supported depends a bit on the running kernel. Further
       information may be available in filesystem-specific files 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:

       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.rst.

   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.

           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 debugfs
       The debugfs filesystem is a pseudo filesystem, traditionally mounted on
       /sys/kernel/debug. As of kernel version 3.4, debugfs has the following

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

           Sets the mode of the mountpoint.

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

       uid=value and gid=value
           This sets the owner or the group of newly created pseudo terminals 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 pseudo
           terminals to belong to the tty group.

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

           Create a private instance of the devpts filesystem, such that indices
           of pseudo terminals 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 pseudo terminal indices (i.e., legacy mode). Each mount of
           devpts with the newinstance option has a private set of pseudo
           terminal 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

           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

   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.

               If current process is in group of file’s group ID, you can change

               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 that the current process is owner of the file,
       or that it has the CAP_FOWNER capability. But FAT filesystems don’t have
       UID/GID on disk, so the normal check is too inflexible. With this option
       you can relax it.

           Three different levels of pickiness can be chosen:

               Upper and lower case are accepted and equivalent, long name parts
               are 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 that contain long parts or special
               characters that are sometimes used on Linux but are not accepted
               by MS-DOS (+, =, etc.) are rejected.

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

           This option is obsolete and may fail or be ignored.

           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.

           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).

           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.

           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.

           Specify FAT behavior on critical errors: panic, continue without
           doing anything, or remount the partition in read-only mode (default

           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.

           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

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

           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

           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.

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

           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.

           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

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

           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 process.

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

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

           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:

           This option is obsolete and may fail or being ignored.

           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).

           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 and execute permission for everybody.) Octal mode
           values require a leading 0.

           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.)

           This option is obsolete and may fail or being ignored.

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

           Select number of session on a multisession CD.

           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.

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

           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 partition.

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

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

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

           These options are accepted but ignored.

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

           New name for the option earlier called iocharset.

           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 gives a
           little-endian encoding and 1 a byteswapped bigendian encoding.

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

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

   Mount options for 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

       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

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

           The upperdir is normally on a writable filesystem.

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

           Use the "user.overlay." xattr namespace instead of
           "trusted.overlay.". This is useful for unprivileged mounting of

           If the redirect_dir feature is enabled, then the directory will be
           copied up (but not the contents). Then the
           "{trusted|user}.overlay.redirect" extended attribute is set to the
           path of the original location from the root of the overlay. Finally
           the directory is moved to the new location.

               Redirects are enabled.

               Redirects are not created and only followed if
               "redirect_always_follow" feature is enabled in the kernel/module

               Redirects are not created, but followed.

               Redirects are not created and not followed (equivalent to
               "redirect_dir=off" if "redirect_always_follow" feature is not

           Inode index. If this feature is disabled and a file with multiple
           hard links is copied up, then this will "break" the link. Changes
           will not be propagated to other names referring to the same inode.

           Can be used to replace UUID of the underlying filesystem in file
           handles with null, and effectively disable UUID checks. This can be
           useful in case the underlying disk is copied and the UUID of this
           copy is changed. This is only applicable if all lower/upper/work
           directories are on the same filesystem, otherwise it will fallback to
           normal behaviour.

           When the underlying filesystems supports NFS export and the
           "nfs_export" feature is enabled, an overlay filesystem may be
           exported to NFS.

           With the “nfs_export” feature, on copy_up of any lower object, an
           index entry is created under the index directory. The index entry
           name is the hexadecimal representation of the copy up origin file
           handle. For a non-directory object, the index entry is a hard link to
           the upper inode. For a directory object, the index entry has an
           extended attribute "{trusted|user}.overlay.upper" with an encoded
           file handle of the upper directory inode.

           When encoding a file handle from an overlay filesystem object, the
           following rules apply

               •   For a non-upper object, encode a lower file handle from lower

               •   For an indexed object, encode a lower file handle from
                   copy_up origin

               •   For a pure-upper object and for an existing non-indexed upper
                   object, encode an upper file handle from upper inode

           The encoded overlay file handle includes

               •   Header including path type information (e.g. lower/upper)

               •   UUID of the underlying filesystem

               •   Underlying filesystem encoding of underlying inode

           This encoding format is identical to the encoding format file handles
           that are stored in extended attribute
           "{trusted|user}.overlay.origin". When decoding an overlay file
           handle, the following steps are followed

               •   Find underlying layer by UUID and path type information.

               •   Decode the underlying filesystem file handle to underlying

               •   For a lower file handle, lookup the handle in index directory
                   by name.

               •   If a whiteout is found in index, return ESTALE. This
                   represents an overlay object that was deleted after its file
                   handle was encoded.

               •   For a non-directory, instantiate a disconnected overlay
                   dentry from the decoded underlying dentry, the path type and
                   index inode, if found.

               •   For a directory, use the connected underlying decoded dentry,
                   path type and index, to lookup a connected overlay dentry.

           Decoding a non-directory file handle may return a disconnected
           dentry. copy_up of that disconnected dentry will create an upper
           index entry with no upper alias.

           When overlay filesystem has multiple lower layers, a middle layer
           directory may have a "redirect" to lower directory. Because middle
           layer "redirects" are not indexed, a lower file handle that was
           encoded from the "redirect" origin directory, cannot be used to find
           the middle or upper layer directory. Similarly, a lower file handle
           that was encoded from a descendant of the "redirect" origin
           directory, cannot be used to reconstruct a connected overlay path. To
           mitigate the cases of directories that cannot be decoded from a lower
           file handle, these directories are copied up on encode and encoded as
           an upper file handle. On an overlay filesystem with no upper layer
           this mitigation cannot be used NFS export in this setup requires
           turning off redirect follow (e.g. "redirect_dir=nofollow").

           The overlay filesystem does not support non-directory connectable
           file handles, so exporting with the subtree_check exportfs
           configuration will cause failures to lookup files over NFS.

           When the NFS export feature is enabled, all directory index entries
           are verified on mount time to check that upper file handles are not
           stale. This verification may cause significant overhead in some

           Note: the mount options index=off,nfs_export=on are conflicting for a
           read-write mount and will result in an error.

           The "xino" feature composes a unique object identifier from the real
           object st_ino and an underlying fsid index. The "xino" feature uses
           the high inode number bits for fsid, because the underlying
           filesystems rarely use the high inode number bits. In case the
           underlying inode number does overflow into the high xino bits,
           overlay filesystem will fall back to the non xino behavior for that

           For a detailed description of the effect of this option please refer

           When metadata only copy up feature is enabled, overlayfs will only
           copy up metadata (as opposed to whole file), when a metadata specific
           operation like chown/chmod is performed. Full file will be copied up
           later when file is opened for WRITE operation.

           In other words, this is delayed data copy up operation and data is
           copied up when there is a need to actually modify data.

           Volatile mounts are not guaranteed to survive a crash. It is strongly
           recommended that volatile mounts are only used if data written to the
           overlay can be recreated without significant effort.

           The advantage of mounting with the "volatile" option is that all
           forms of sync calls to the upper filesystem are omitted.

           In order to avoid a giving a false sense of safety, the syncfs (and
           fsync) semantics of volatile mounts are slightly different than that
           of the rest of VFS. If any writeback error occurs on the upperdir’s
           filesystem after a volatile mount takes place, all sync functions
           will return an error. Once this condition is reached, the filesystem
           will not recover, and every subsequent sync call will return an
           error, even if the upperdir has not experience a new error since the
           last sync call.

           When overlay is mounted with "volatile" option, the directory
           "$workdir/work/incompat/volatile" is created. During next mount,
           overlay checks for this directory and refuses to mount if present.
           This is a strong indicator that user should throw away upper and work
           directories and create fresh one. In very limited cases where the
           user knows that the system has not crashed and contents of upperdir
           are intact, The "volatile" directory can be removed.

   Mount options for reiserfs
       Reiserfs is a journaling filesystem.

           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

               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.

               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.

               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.

               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 situations.

           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.

           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(1) manual page.

           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

              UBI device number X, volume number Y

              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 filesystem. 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 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.

           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

           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".

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

           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

           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

           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

           Show otherwise hidden files.

           Show deleted files in lists.

           Embed data in the inode. (default)

           Don’t embed data in the inode.

           Use short UDF address descriptors.

           Use long UDF address descriptors. (default)

           Unset strict conformance.

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

           Set the UTF-8 character set.

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

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

           Override standard anchor location. (default= 256)

           Set the last block of the filesystem.

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

           Ignored, use gid=<group> instead.

           Unimplemented and ignored.

           Unimplemented and ignored.

           Unimplemented and ignored.

           Unimplemented and ignored.

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

               For filesystems created by a BSD-like system (NetBSD, FreeBSD,

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

               Synonym for ufs2.

               For filesystems created by SunOS or Solaris on Sparc.

               For filesystems created by Solaris on x86.

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

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

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

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

           Set behavior on error:

               If an error is encountered, cause a kernel panic.

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

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

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

           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).

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

           First try to make a short name without sequence number, before trying

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

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

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

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

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

               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

   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

       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

       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 device-mapper verity target provides read-only transparent integrity
       checking of block devices using kernel crypto API. The mount command can
       open the dm-verity device and do the integrity verification before on the
       device filesystem is mounted. Requires libcryptsetup with in libmount
       (optionally via dlopen(3)). If libcryptsetup supports extracting the root
       hash of an already mounted device, existing devices will be automatically
       reused in case of a match. Mount options for dm-verity:

           Path to the hash tree device associated with the source volume to
           pass to dm-verity.

           Hex-encoded hash of the root of verity.hashdevice. Mutually exclusive
           with verity.roothashfile.

           Path to file containing the hex-encoded hash of the root of
           verity.hashdevice. Mutually exclusive with verity.roothash.

           If the hash tree device is embedded in the source volume, offset
           (default: 0) is used by dm-verity to get to the tree.

           Path to the Forward Error Correction (FEC) device associated with the
           source volume to pass to dm-verity. Optional. Requires kernel built
           with CONFIG_DM_VERITY_FEC.

           If the FEC device is embedded in the source volume, offset (default:
           0) is used by dm-verity to get to the FEC area. Optional.

           Parity bytes for FEC (default: 2). Optional.

           Path to pkcs7(1ssl) signature of root hash hex string. Requires
           crypt_activate_by_signed_key() from cryptsetup and kernel built with
           CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG. For device reuse, signatures
           have to be either used by all mounts of a device or by none.

       Supported since util-linux v2.35.

       For example commands:

           mksquashfs /etc /tmp/etc.squashfs
           dd if=/dev/zero of=/tmp/etc.hash bs=1M count=10
           veritysetup format /tmp/etc.squashfs /tmp/etc.hash
           openssl smime -sign -in <hash> -nocerts -inkey private.key \
           -signer private.crt -noattr -binary -outform der -out /tmp/etc.roothash.p7s
           mount -o verity.hashdevice=/tmp/etc.hash,verity.roothash=<hash>,\
           verity.roothashsig=/tmp/etc.roothash.p7s /tmp/etc.squashfs /mnt

       create squashfs image from /etc directory, verity hash device and mount
       verified filesystem image to /mnt. The kernel will verify that the root
       hash is signed by a key from the kernel keyring if roothashsig is used.

       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 re-uses the loop device rather than
       initializing 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.

       mount has the following exit status values (the bits can be ORed):


           incorrect invocation or permissions

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

           internal mount bug

           user interrupt

           problems writing or locking /etc/mtab

           mount failure

           some mount succeeded

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

       The syntax of external mount helpers is:

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

       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

       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 an
       argument to the -o option.

           overrides the default location of the fstab file (ignored for suid)

           overrides the default location of the mtab file (ignored for suid)

           enables libmount debug output

           enables libblkid debug output

           enables loop device setup debug output

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

           filesystem table

           libmount private runtime directory

           table of mounted filesystems or symlink to /proc/mounts

           lock file (unused on systems with mtab symlink)

           temporary file (unused on systems with mtab symlink)

           a list of filesystem types to try

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

       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, 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/mount 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 the
       noac mount option 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(8) command manually before calling
       mount with the configured loop device.

       Karel Zak <>

       mount(2), umount(2), filesystems(5), fstab(5), nfs(5), xfs(5),
       mount_namespaces(7), xattr(7), e2label(8), findmnt(8), losetup(8),
       lsblk(8), mke2fs(8), mountd(8), nfsd(8), swapon(8), tune2fs(8),
       umount(8), xfs_admin(8)

       For bug reports, use the issue tracker at

       The mount command is part of the util-linux package which can be
       downloaded from Linux Kernel Archive

util-linux 2.37.2                  2021-08-16                           MOUNT(8)