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.
+files. A lazy unmount avoids this problem, but it may introduce another
+issues. See \fB\-\-lazy\fR description below.
.SH OPTIONS
.TP
.BR \-a , " \-\-all"
All of the filesystems described in
-.I /etc/mtab
-are unmounted, except the \fIproc\fR filesystem.
+.I /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 \fB\-\-types\fR
+umount option.
.TP
-.BR \-A , " \-\-all-targets"
-Unmount all mountpoints in the current namespace for the specified filesystem.
+.BR \-A , " \-\-all\-targets"
+Unmount 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 \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 \-c , " \-\-no\-canonicalize"
+Do not canonicalize paths. The paths canonicalization is based on
+.BR stat (2)
+and
+.BR 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
.BR mount (8)
-man page. Note that \fBumount\fR does not pass this option to the
+man page. Note that \fBumount\fR does not pass this option to the
.BI /sbin/umount. type
helpers.
.TP
-.BR \-d , " \-\-detach-loop"
+.BR \-d , " \-\-detach\-loop"
When the unmounted device was a loop device, also free this loop
-device.
+device. This option is unnecessary for devices initialized by
+.BR mount (8),
+in this case "autoclear" functionality is enabled by default.
.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
+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
.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.)
+Force 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.
.TP
-.BR \-i , " \-\-internal-only"
+.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.)
+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 \fBumount \-l\fR 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.
+
+.TP
+.BR \-N , " \-\-namespace " \fIns
+Perform umount in the mount namespace specified by \fIns\fR.
+\fIns\fR is either PID of process running in that namespace
+or special file representing that namespace.
+.sp
+.BR umount (8)
+switches to the namespace when it reads /etc/fstab, writes /etc/mtab (or writes to /run/mount) and calls
+.BR 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 another requirements necessary to execute
+.BR umount (2)
+command.
+.sp
+See \fBmount_namespaces\fR(7) for more information.
.TP
-.BR \-n , " \-\-no-mtab"
+.BR \-n , " \-\-no\-mtab"
Unmount without writing in
.IR /etc/mtab .
.TP
-.BR \-O , " \-\-test-opts " \fIoption\fR...
+.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.
.B no
to indicate that no action should be taken for this option.
.TP
+.BR \-q , " \-\-quiet"
+Suppress "not mounted" error messages.
+.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
must be specified by mountpoint path; a recursive unmount by device name (or UUID)
is unsupported.
.TP
-.BR \-r , " \-\-read-only"
+.BR \-r , " \-\-read\-only"
When an unmount fails, try to remount the filesystem read-only.
.TP
.BR \-t , " \-\-types " \fItype\fR...
of filesystem types can be prefixed with
.B no
to indicate that no action should be taken for all of the mentioned types.
+Note that
+.B 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").
.TP
.BR \-v , " \-\-verbose"
Verbose mode.
.TP
.BR \-h , " \-\-help"
Display help text and exit.
-.SH "LOOP DEVICE"
+.SH NON-SUPERUSER UMOUNTS
+Normally, only the superuser can umount filesystems.
+However, when
+.I fstab
+contains the
+.B user
+option on a line, anybody can umount the corresponding filesystem. For more details see
+.BR mount (8)
+man page.
+.PP
+Since version 2.34 \fBumount\fR command allows 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.
+.PP
+Since version 2.35 \fBumount\fR 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. It allows to support use-cases where
+root permissions are not necessary (e.g., fuse filesystems, user namespaces,
+etc).
+.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"
+command will automatically detach loop device previously initialized by
+.BR mount (8)
+command independently of /etc/mtab.
+
+In this case the device is initialized with "autoclear" flag (see
+.BR losetup (8)
+output for more details), otherwise it's necessary to use the option \fB \-\-detach\-loop\fR
+or call \fBlosetup \-d <device>\fR. The autoclear feature is supported since Linux 2.6.25.
+.SH EXTERNAL HELPERS
The syntax of external unmount helpers is:
.PP
-.BI /sbin/umount. suffix
+.RS
+.BI umount. suffix
.RI { directory | device }
.RB [ \-flnrv ]
+.RB [ \-N
+.IR namespace ]
.RB [ \-t
.IR type . subtype ]
+.RE
.PP
-where \fIsuffix\fR is the filesystem type or a value from a "uhelper=" or
-"helper=" mtab option. The \fB\-t\fR option can be used for filesystems
-with subtypes support (for example \fB/sbin/mount.fuse -t fuse.sshfs\fR).
+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
-The \fBuhelper=\fR (unprivileged unmount helper) mount option can be used
-when non-root users need to be able to unmount a mountpoint which is not
-defined in \fI/etc/fstab\fR (e.g. devices mounted by udisk).
+.RS
+.B umount.fuse \-t fuse.sshfs
+.RE
.PP
-The \fBhelper=\fR mount option redirects 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
-checked when option \fB\-O\fR is given
+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.
+.PP
+Note that \fI/etc/mtab\fR is currently deprecated and helper= and another
+userspace mount options are maintained by libmount.
.SH ENVIRONMENT
.IP LIBMOUNT_FSTAB=<path>
-overrides the default location of the fstab file
+overrides the default location of the fstab file (ignored for suid)
.IP LIBMOUNT_MTAB=<path>
-overrides the default location of the mtab file
-.IP LIBMOUNT_DEBUG=0xffff
-enables debug output
-.SH "SEE ALSO"
-.BR umount (2),
-.BR mount (8),
-.BR losetup (8)
+overrides the default location of the mtab file (ignored for suid)
+.IP LIBMOUNT_DEBUG=all
+enables libmount debug output
+.SH FILES
+.TP
+.I /etc/mtab
+table of mounted filesystems (deprecated and usually replaced by
+symlink to /proc/mounts)
+.TP
+.I /etc/fstab
+table of known filesystems
+.TP
+.I /proc/self/mountinfo
+table of mounted filesystems generated by kernel.
.SH HISTORY
A
.B umount
command appeared in Version 6 AT&T UNIX.
+.SH SEE ALSO
+.BR umount (2),
+.BR losetup (8),
+.BR mount_namespaces (7)
+.BR mount (8)
.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/
+.UR https://\:www.kernel.org\:/pub\:/linux\:/utils\:/util-linux/
Linux Kernel Archive
.UE .
projects / thirdparty / util-linux.git / blobdiff