UMOUNT
Section: System Administration (8)
Updated: July 2014
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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also work, but is obsolete, mainly because it will fail in case this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.
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). (Requires kernel
2.1.116 or later.)
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. (Requires kernel 2.4.11 or later.)
- -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.
- -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.
Notethat
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.
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]
[-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
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- OPTIONS
-
- LOOP DEVICE
-
- EXTERNAL HELPERS
-
- FILES
-
- ENVIRONMENT
-
- SEE ALSO
-
- HISTORY
-
- AVAILABILITY
-
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