centos man page for umount

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  Giving the special device on which the file system lives may also work, but is obsolete, mainly because it will  fail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  file  systems  described  in  /etc/mtab are unmounted.  (With umount version 2.7 and later: the proc filesystem is not
	      unmounted.)

       -A, --all-targets
	      Unmount all mountpoints in the current namespace for the specified filesystem.  The filesystem could be  specified  by  one  of  the
	      mountpoints  or  device  name (or UUID, etc.). This option could be used together with --recursive then all nested mounts within the
	      filesystem are recursively unmounted.

       -c, --no-canonicalize
	      Do not canonicalize paths.  For more details about this option see the mount(8) man page.

       -d, --detach-loop
	      In case the unmounted device was a loop device, also free this loop device.

       --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.

       -f, --force
	      Force unmount (in case of an unreachable NFS system).  (Requires kernel 2.1.116 or later.)

       -i, --internal-only
	      Do  not  call  the /sbin/umount.<filesystem> helper even if it exists.  By default /sbin/umount.<filesystem> helper is called if one
	      exists.

       -n, --no-mtab
	      Unmount without writing in /etc/mtab.

       -l, --lazy
	      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.)

       -O, --test-opts options,list
	      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.

       -R, --recursive
	      Recursively unmount each directory specified. 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, recursive unmount by device name (or UUID) is unsupported.

       -r, --read-only
	      In case unmounting fails, try to remount read-only.

       -t, --types vfstype,ext2,ext3
	      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 system types  on  which	no  action
	      should be taken.

       -v, --verbose
	      Verbose mode.

       -h, --help
	      Print help message and exit.

       -V, --version
	      Print version and exit.

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.<suffix> {dir|device} [-nlfvr] [-t type.subtype]

       where the <suffix> is filesystem type or a value from "uhelper=" or "helper=" mtab option.  The -t option is used for filesystems with sub-
       types 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.<helper> independently on UID.

FILES
       /etc/mtab table of mounted file systems

ENVIRONMENT
       LIBMOUNT_FSTAB=<path>
	      overrides the default location of the fstab file

       LIBMOUNT_MTAB=<path>
	      overrides the default location of the mtab file

       LIBMOUNT_DEBUG=0xffff
	      enables debug output

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 Linux Kernel Archive <ftp://ftp.kernel.org/pub/linux/utils/util-
       linux/>.

util-linux							    August 2012 							 UMOUNT(8)