UMOUNT(8) System Administration UMOUNT(8)
NAME
umount - unmount file systems
SYNOPSIS
umount [-hV]
umount -a [-dflnrv] [-t vfstype] [-O options]
umount [-dflnrv] {dir|device}...
DESCRIPTION
The umount command detaches the file system(s) mentioned 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 obso‐
lete, 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 for the umount command:
-V Print version and exit.
-h Print help message and exit.
-v Verbose mode.
-n Unmount without writing in /etc/mtab.
-r In case unmounting fails, try to remount read-only.
-d In case the unmounted device was a loop device, also free this loop device.
-i Don't call the /sbin/umount. helper even if it exists. By default /sbin/umount. helper is
called if one exists.
-a All of the file systems described in /etc/mtab are unmounted. (With umount version 2.7 and later: the proc filesys‐
tem is not unmounted.)
-t vfstype
Indicate that the actions should only be taken on file systems of the specified type. More than one type may be
specified in a comma separated list. The list of file system types can be prefixed with no to specify the file sys‐
tem types on which no action should be taken.
-O options
Indicate that the actions should only be taken on file systems with the specified options in /etc/fstab. More than
one option type may be specified in a comma separated list. Each option can be prefixed with no to specify options
for which no action should be taken.
-f Force unmount (in case of an unreachable NFS system). (Requires kernel 2.1.116 or later.)
-l Lazy unmount. Detach the filesystem from the filesystem hierarchy now, and cleanup all references to the filesystem
as soon as it is not busy anymore. (Requires kernel 2.4.11 or later.)
--no-canonicalize
Don't canonicalize paths. For more details about this option see the mount(8) man page.
--fake Causes everything to be done except for the actual system call; this ``fakes'' unmounting the filesystem. It can
be used to remove entries from /etc/mtab that were unmounted earlier with the -n option.
THE LOOP DEVICE
The umount command will free the loop device (if any) associated with the mount, in case it finds the option `loop=...' in
/etc/mtab, or when the -d option was given. Any pending loop devices can be freed using `losetup -d', see losetup(8).
NOTES
The syntax of external umount helpers is:
/sbin/umount. {dir|device} [-nlfvr] [-t type.subtype]
where the is filesystem type or a value from "uhelper=" or "helper=" mtab option. The -t option is used for
filesystems with subtypes support (for example /sbin/mount.fuse -t fuse.sshfs).
The uhelper= (unprivileged umount helper) is possible to use when non-root user wants to umount a mountpoint which is not
defined in the /etc/fstab file (e.g devices mounted by udisk).
The helper= mount option redirects all umount requests to the /sbin/umount. independently on UID.
FILES
/etc/mtab table of mounted file systems
SEE ALSO
umount(2), mount(8), losetup(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 ftp://ftp.kernel.org/pub/linux/utils/util-
linux/.
util-linux March 2010 UMOUNT(8)
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