sys-utils/umount.8

.\" Copyright (c) 1996 Andries Brouwer
.\" This page is somewhat derived from a page that was
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.\" and had been heavily modified by Rik Faith and myself.
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.TH UMOUNT 8 "July 2014" "util-linux" "System Administration"
.SH NAME
umount \- unmount file systems
.SH SYNOPSIS
.B umount \-a
.RB [ \-dflnrv ]
.RB [ \-t
.IR fstype ]
.RB [ \-O
.IR option ...]
.sp
.B umount
.RB [ \-dflnrv ]
.RI { directory | device }...
.sp
.B umount
.BR \-h | \-V

.SH DESCRIPTION
The
.B 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also work, but is obsolete, mainly because it will fail in case this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.
.PP
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
.B umount
itself - it opens libc, and libc in its turn may open for example locale
files.  A lazy unmount avoids this problem.
.SH OPTIONS
.TP
.BR \-a , " \-\-all"
All of the filesystems described in
.I /etc/mtab
are unmounted, except the \fIproc\fR filesystem.
.TP
.BR \-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 \fB\-\-recursive\fR, 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.
.TP
.BR \-c , " \-\-no\-canonicalize"
Do not canonicalize paths.  For more details about this option see the
.BR mount (8)
man page.  Note that \fBumount\fR does not pass this option to the
.BI /sbin/umount. type
helpers.
.TP
.BR \-d , " \-\-detach\-loop"
When the unmounted device was a loop device, also free this loop
device.
.TP
.B \-\-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
.I /etc/mtab
that were unmounted earlier with the
.B \-n
option.
.TP
.BR \-f , " \-\-force"
Force an unmount (in case of an unreachable NFS system).  (Requires kernel
2.1.116 or later.)
.TP
.BR \-i , " \-\-internal\-only"
Do not call the \fB/sbin/umount.\fIfilesystem\fR helper even if it exists.
By default such a helper program is called if it exists.
.TP
.BR \-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.)
.TP
.BR \-n , " \-\-no\-mtab"
Unmount without writing in
.IR /etc/mtab .
.TP
.BR \-O , " \-\-test\-opts " \fIoption\fR...
Unmount only the filesystems that have the specified option set in
.IR /etc/fstab .
More than one option may be specified in a comma-separated list.
Each option can be prefixed with
.B no
to indicate that no action should be taken for this option.
.TP
.BR \-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.
.TP
.BR \-r , " \-\-read\-only"
When an unmount fails, try to remount the filesystem read-only.
.TP
.BR \-t , " \-\-types " \fItype\fR...
Indicate that the actions should only be taken on filesystems of the
specified
.IR type .
More than one type may be specified in a comma-separated list.  The list
of filesystem types can be prefixed with
.B no
to indicate that no action should be taken for all of the mentioned types.
.TP
.BR \-v , " \-\-verbose"
Verbose mode.
.TP
.BR \-V , " \-\-version"
Display version information and exit.
.TP
.BR \-h , " \-\-help"
Display help text and exit.
.SH "LOOP DEVICE"
The
.B umount
command will free the loop device associated with a mount when
it finds the option \fBloop=...\fR in
.IR /etc/mtab ,
or when the \fB\-d\fR option was given.  Any still associated loop devices
can be freed by using \fBlosetup -d\fR; see
.BR losetup (8).
.SH EXTERNAL HELPERS
The syntax of external unmount helpers is:
.PP
.RS
.BI umount. suffix
.RI { directory | device }
.RB [ \-flnrv ]
.RB [ \-t
.IR type . subtype ]
.RE
.PP
where \fIsuffix\fR is the filesystem type (or the value from a
\fBuhelper=\fR or \fBhelper=\fR marker in the mtab file).
The \fB\-t\fR option can be used for filesystems that
have subtype support.  For example:
.PP
.RS
.B umount.fuse \-t fuse.sshfs
.RE
.PP
A \fBuhelper=\fIsomething\fR marker (unprivileged helper) can appear in
the \fI/etc/mtab\fR file when ordinary users need to be able to unmount
a mountpoint that is not defined in \fI/etc/fstab\fR
(for example for a device that was mounted by \fBudisks\fR(1)).
.PP
A \fBhelper=\fItype\fR marker in the mtab file will redirect
all unmount requests
to the \fB/sbin/umount.\fItype\fR helper independently of UID.
.SH FILES
.TP
.B /etc/mtab
table of mounted filesystems
.TP
.B /etc/fstab
table of known filesystems
.SH ENVIRONMENT
.IP LIBMOUNT_FSTAB=<path>
overrides the default location of the fstab file (ignored for suid)
.IP LIBMOUNT_MTAB=<path>
overrides the default location of the mtab file (ignored for suid)
.IP LIBMOUNT_DEBUG=all
enables libmount debug output
.SH "SEE ALSO"
.BR umount (2),
.BR mount (8),
.BR losetup (8)
.SH HISTORY
A
.B umount
command appeared in Version 6 AT&T UNIX.
.SH AVAILABILITY
The umount command is part of the util-linux package and is available from
.UR ftp://\:ftp.kernel.org\:/pub\:/linux\:/utils\:/util-linux/
Linux Kernel Archive
.UE .