umount — unmount filesystems
umount \-a [−dflnrv] [ −t fstype ] [ −O option... ]
umount [−dflnrv] directory | device ...
umount −h | −V
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 Giving the special device on which the filesystem lives may also work, but is obsolete, mainly because it will fail in case this device was mounted on more than one directory.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.
−a,
−−allAll 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−targetsUnmount 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−canonicalizeDo 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−loopWhen 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.
−−fakeCauses 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,
−−forceForce 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−onlyDo not call the /sbin/umount.filesystem helper
even if it exists. By default such a helper program is
called if it exists.
−l,
−−lazyLazy 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 nsPerform 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−mtabUnmount 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,
−−quietSuppress "not mounted" error messages.
−R,
−−recursiveRecursively 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−onlyWhen 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,
−−verboseVerbose mode.
−V,
−−versionDisplay version information and exit.
−h,
−−helpDisplay help text and exit.
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).
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.
The syntax of external unmount helpers is:
umount.suffix {directory|device} [−flnrv] [−Nnamespace] [−ttype.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.
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=allenables libmount debug output
/etc/mtabtable of mounted filesystems (deprecated and usually
replaced by symlink to /proc/mounts)
/etc/fstabtable of known filesystems
/proc/self/mountinfotable of mounted filesystems generated by kernel.
The umount command is part of the util-linux package and is available from Linux Kernel Archive
|
Copyright (c) 1996 Andries Brouwer This page is somewhat derived from a page that was (c) 1980, 1989, 1991 The Regents of the University of California and had been heavily modified by Rik Faith and myself. This is free documentation; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. The GNU General Public License's references to "object code" and "executables" are to be interpreted as the output of any document formatting or typesetting system, including intermediate and printed output. This manual is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. |