umount(8) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | NON-SUPERUSER UMOUNTS | LOOP DEVICE | EXTERNAL HELPERS | ENVIRONMENT | FILES | HISTORY | SEE ALSO | AVAILABILITY | COLOPHON

UMOUNT(8)                 System Administration                UMOUNT(8)

NAME         top

       umount - unmount filesystems

SYNOPSIS         top

       umount -a [-dflnrv] [-t fstype] [-O option...]

       umount [-dflnrv] {directory|device}...

       umount -h|-V

DESCRIPTION         top

       The umount command detaches the mentioned filesystem(s) from the
       file hierarchy.  A filesystem is specified by giving the
       directory where it has been mounted.  Giving the special device
       on which the filesystem lives may also work, but is obsolete,
       mainly because it will fail in case this device was mounted on
       more than one directory.

       Note that a filesystem cannot be unmounted when it is 'busy' -
       for example, when there are open files on it, or when some
       process has its working directory there, or when a swap file on
       it is in use.  The offending process could even be umount itself
       - it opens libc, and libc in its turn may open for example locale
       files.  A lazy unmount avoids this problem, but it may introduce
       other issues. See --lazy description below.

OPTIONS         top

       -a, --all
              All of the filesystems described in /proc/self/mountinfo
              (or in deprecated /etc/mtab) are unmounted, except the
              proc, devfs, devpts, sysfs, rpc_pipefs and nfsd
              filesystems. This list of the filesystems may be replaced
              by --types umount option.

       -A, --all-targets
              Unmount all mountpoints in the current mount namespace for
              the specified filesystem.  The filesystem can be specified
              by one of the mountpoints or the device name (or UUID,
              etc.).  When this option is used together with
              --recursive, then all nested mounts within the filesystem
              are recursively unmounted.  This option is only supported
              on systems where /etc/mtab is a symlink to /proc/mounts.

       -c, --no-canonicalize
              Do not canonicalize paths.  The paths canonicalization is
              based on stat(2) and readlink(2) system calls. These
              system calls may hang in some cases (for example on NFS if
              server is not available). The option has to be used with
              canonical path to the mount point.

              This option is silently ignored by umount for non-root
              users.

              For more details about this option see the mount(8) man
              page. Note that umount does not pass this option to the
              /sbin/umount.type helpers.

       -d, --detach-loop
              When the unmounted device was a loop device, also free
              this loop device. This option is unnecessary for devices
              initialized by mount(8), in this case "autoclear"
              functionality is enabled by default.

       --fake Causes everything to be done except for the actual system
              call or umount helper execution; this 'fakes' unmounting
              the filesystem.  It can be used to remove entries from the
              deprecated /etc/mtab that were unmounted earlier with the
              -n option.

       -f, --force
              Force an unmount (in case of an unreachable NFS system).

              Note that this option does not guarantee that umount
              command does not hang.  It's strongly recommended to use
              absolute paths without symlinks to avoid unwanted readlink
              and stat system calls on unreachable NFS in umount.

       -i, --internal-only
              Do not call the /sbin/umount.filesystem helper even if it
              exists.  By default such a helper program is called if it
              exists.

       -l, --lazy
              Lazy unmount.  Detach the filesystem from the file
              hierarchy now, and clean up all references to this
              filesystem as soon as it is not busy anymore.

              A system reboot would be expected in near future if you're
              going to use this option for network filesystem or local
              filesystem with submounts.  The recommended use-case for
              umount -l is to prevent hangs on shutdown due to an
              unreachable network share where a normal umount will hang
              due to a downed server or a network partition. Remounts of
              the share will not be possible.

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

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

              See mount_namespaces(7) for more information.

       -n, --no-mtab
              Unmount without writing in /etc/mtab.

       -O, --test-opts option...
              Unmount only the filesystems that have the specified
              option set in /etc/fstab.  More than one option may be
              specified in a comma-separated list.  Each option can be
              prefixed with no to indicate that no action should be
              taken for this option.

       -q, --quiet
              Suppress "not mounted" error messages.

       -R, --recursive
              Recursively unmount each specified directory.  Recursion
              for each directory will stop if any unmount operation in
              the chain fails for any reason.  The relationship between
              mountpoints is determined by /proc/self/mountinfo entries.
              The filesystem must be specified by mountpoint path; a
              recursive unmount by device name (or UUID) is unsupported.

       -r, --read-only
              When an unmount fails, try to remount the filesystem read-
              only.

       -t, --types type...
              Indicate that the actions should only be taken on
              filesystems of the specified type.  More than one type may
              be specified in a comma-separated list.  The list of
              filesystem types can be prefixed with no to indicate that
              no action should be taken for all of the mentioned types.
              Note that umount reads information about mounted
              filesystems from kernel (/proc/mounts) and filesystem
              names may be different than filesystem names used in the
              /etc/fstab (e.g., "nfs4" vs. "nfs").

       -v, --verbose
              Verbose mode.

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

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

NON-SUPERUSER UMOUNTS         top

       Normally, only the superuser can umount filesystems.  However,
       when fstab contains the user option on a line, anybody can umount
       the corresponding filesystem.  For more details see mount(8) man
       page.

       Since version 2.34 the umount command can be used to perform
       umount operation also for fuse filesystems if kernel mount table
       contains user's ID.  In this case fstab user= mount option is not
       required.

       Since version 2.35 umount command does not exit when user
       permissions are inadequate by internal libmount security rules.
       It drops suid permissions and continue as regular non-root user.
       This can be used to support use-cases where root permissions are
       not necessary (e.g., fuse filesystems, user namespaces, etc).

LOOP DEVICE         top

       The umount command will automatically detach loop device
       previously initialized by mount(8) command independently of
       /etc/mtab.

       In this case the device is initialized with "autoclear" flag (see
       losetup(8) output for more details), otherwise it's necessary to
       use the option  --detach-loop or call losetup -d <device>. The
       autoclear feature is supported since Linux 2.6.25.

EXTERNAL HELPERS         top

       The syntax of external unmount helpers is:

              umount.suffix {directory|device} [-flnrv] [-N namespace]
              [-t type.subtype]

       where suffix is the filesystem type (or the value from a uhelper=
       or helper= marker in the mtab file).  The -t option can be used
       for filesystems that have subtype support.  For example:

              umount.fuse -t fuse.sshfs

       A uhelper=something marker (unprivileged helper) can appear in
       the /etc/mtab file when ordinary users need to be able to unmount
       a mountpoint that is not defined in /etc/fstab (for example for a
       device that was mounted by udisks(1)).

       A helper=type marker in the mtab file will redirect all unmount
       requests to the /sbin/umount.type helper independently of UID.

       Note that /etc/mtab is currently deprecated and helper= and other
       userspace mount options are maintained by libmount.

ENVIRONMENT         top

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

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

       LIBMOUNT_DEBUG=all
              enables libmount debug output

FILES         top

       /etc/mtab
              table of mounted filesystems (deprecated and usually
              replaced by symlink to /proc/mounts)

       /etc/fstab
              table of known filesystems

       /proc/self/mountinfo
              table of mounted filesystems generated by kernel.

HISTORY         top

       A umount command appeared in Version 6 AT&T UNIX.

SEE ALSO         top

       umount(2), losetup(8), mount_namespaces(7) mount(8)

AVAILABILITY         top

       The umount command is part of the util-linux package and is
       available from Linux Kernel Archive 
       ⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩.

COLOPHON         top

       This page is part of the util-linux (a random collection of Linux
       utilities) project.  Information about the project can be found
       at ⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩.  If you
       have a bug report for this manual page, send it to
       util-linux@vger.kernel.org.  This page was obtained from the
       project's upstream Git repository
       ⟨git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git⟩ on
       2021-03-21.  (At that time, the date of the most recent commit
       that was found in the repository was 2021-03-19.)  If you
       discover any rendering problems in this HTML version of the page,
       or you believe there is a better or more up-to-date source for
       the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original
       manual page), send a mail to man-pages@man7.org

util-linux                      July 2014                      UMOUNT(8)

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