UMOUNT(8) System Administration UMOUNT(8)
NAME
umount - unmount filesystems
SYNOPSIS
umount -a [-dflnrv] [-t fstype] [-O option...]
umount [-dflnrv] {directory|device}
umount -h|-V
DESCRIPTION
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lives may also work, but is obsolete, mainly because it will fail in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
-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(2) and stat(2) 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 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. Since version 2.37 it umounts also all over-mounted
filesystems (more filesystems on the same mountpoint).
-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.
-h, --help
Display help text and exit.
-V, --version
Print version 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 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
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 other
userspace mount options are maintained by libmount.
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
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.
HISTORY
A umount command appeared in Version 6 AT&T UNIX.
SEE ALSO
umount(2), losetup(8), mount_namespaces(7), mount(8)
REPORTING BUGS
For bug reports, use the issue tracker at
https://github.com/util-linux/util-linux/issues.
AVAILABILITY
The umount command is part of the util-linux package which can be
downloaded from Linux Kernel Archive
<https://www.kernel.org/pub/linux/utils/util-linux/>.
util-linux 2.38.1 2022-08-04 UMOUNT(8)
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