umount

UMOUNT(8)                    System Administration                   UMOUNT(8)



NAME
       umount - unmount file systems

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

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

       umount -h|-V


DESCRIPTION
       The umount command detaches the mentioned file system(s) from the file
       hierarchy.  A file system is specified by giving the directory where it
       has been mounted.  Giving the special device on which the file system
       lives may also work, but is obsolete, mainly because it will fail in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 file system 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 another issues. See --lazy
       description below.

OPTIONS
       -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 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.

              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 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 namespace does not have to contain any
              libraries or another requirements necessary to execute umount(2)
              command.

              See 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
       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 umount command allows 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. It allows to support
       use-cases where root permissions are not necessary (e.g., fuse
       filesystems, user namespaces, etc).

LOOP DEVICE
       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
       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 another
       userspace mount options are maintained by libmount.

FILES
       /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.

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

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

       LIBMOUNT_DEBUG=all
              enables libmount debug output

SEE ALSO
       umount(2), losetup(8), mount(8)

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

AVAILABILITY
       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/⟩.



util-linux                         July 2014                         UMOUNT(8)