sys-utils/umount.8.adoc

   1 //po4a: entry man manual
   2 ////
   3 Copyright (c) 1996 Andries Brouwer
   4 This page is somewhat derived from a page that was
   5 (c) 1980, 1989, 1991 The Regents of the University of California
   6 and had been heavily modified by Rik Faith and myself.
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  21 GNU General Public License for more details.
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  26 ////
  27 = umount(8)
  28 :doctype: manpage
  29 :man manual: System Administration
  30 :man source: util-linux {release-version}
  31 :page-layout: base
  32 :command: umount
  33
  34 == NAME
  35
  36 umount - unmount filesystems
  37
  38 == SYNOPSIS
  39
  40 *umount* *-a* [*-dflnrv*] [*-t* _fstype_] [*-O* _option_...]
  41
  42 *umount* [*-dflnrv*] {_directory_|_device_}
  43
  44 *umount* *-h*|*-V*
  45
  46 == DESCRIPTION
  47
  48 The *umount* command detaches the mentioned filesystem(s) from the file hierarchy. A filesystem is specified by giving the directory where it has been mounted. Giving the special device on which the filesystem lives may also work, but is obsolete, mainly because it will fail in case this device was mounted on more than one directory.
  49
  50 Note that a filesystem 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, but it may introduce other issues. See *--lazy* description below.
  51
  52 == OPTIONS
  53
  54 *-a*, *--all*::
  55 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.
  56
  57 *-A*, *--all-targets*::
  58 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 *--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_.
  59
  60 *-c*, *--no-canonicalize*::
  61 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.
  62 +
  63 This option is silently ignored by *umount* for non-root users.
  64 +
  65 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.
  66
  67 *-d*, *--detach-loop*::
  68 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.
  69
  70 *--fake*::
  71 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.
  72
  73 *-f*, *--force*::
  74 Force an unmount (in case of an unreachable NFS system).
  75 +
  76 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*(2) and *stat*(2) system calls on unreachable NFS in *umount*.
  77
  78 *-i*, *--internal-only*::
  79 Do not call the **/sbin/umount.**__filesystem__ helper even if it exists. By default such a helper program is called if it exists.
  80
  81 *-l*, *--lazy*::
  82 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.
  83 +
  84 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 *umount -l* 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.
  85
  86 *-N*, *--namespace* _ns_::
  87 Perform *umount* in the mount namespace specified by _ns_. _ns_ is either PID of process running in that namespace or special file representing that namespace.
  88 +
  89 *umount* switches to the namespace when it reads _/etc/fstab_, writes _/etc/mtab_ (or writes to _/run/mount_) and calls *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 other requirements necessary to execute *umount*(2) command.
  90 +
  91 See *mount_namespaces*(7) for more information.
  92
  93 *-n*, *--no-mtab*::
  94 Unmount without writing in _/etc/mtab_.
  95
  96 *-O*, *--test-opts* _option_...::
  97 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.
  98
  99 *-q*, *--quiet*::
 100 Suppress "not mounted" error messages.
 101
 102 *-R*, *--recursive*::
 103 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. Since version 2.37 it umounts also all over-mounted filesystems (more filesystems on the same mountpoint).
 104
 105 *-r*, *--read-only*::
 106 When an unmount fails, try to remount the filesystem read-only.
 107
 108 *-t*, *--types* _type_...::
 109 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. Note that *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").
 110
 111 *-v*, *--verbose*::
 112 Verbose mode.
 113
 114 include::man-common/help-version.adoc[]
 115
 116 == NON-SUPERUSER UMOUNTS
 117
 118 Normally, only the superuser can umount filesystems. However, when _fstab_ contains the *user* option on a line, anybody can umount the corresponding filesystem. For more details see *mount*(8) man page.
 119
 120 Since version 2.34 the *umount* command can be used 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.
 121
 122 Since version 2.35 *umount* 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. This can be used to support use-cases where root permissions are not necessary (e.g., fuse filesystems, user namespaces, etc).
 123
 124 == LOOP DEVICE
 125
 126 The *umount* command will automatically detach loop device previously initialized by *mount*(8) command independently of _/etc/mtab_.
 127
 128 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.
 129
 130 == EXTERNAL HELPERS
 131
 132 The syntax of external unmount helpers is:
 133
 134 ____
 135 **umount.**__suffix__ {__directory__|_device_} [*-flnrv*] [*-N* _namespace_] [*-t* _type_._subtype_]
 136 ____
 137
 138 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:
 139
 140 ____
 141 *umount.fuse -t fuse.sshfs*
 142 ____
 143
 144 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)).
 145
 146 A **helper=**__type__ marker in the _mtab_ file will redirect all unmount requests to the **/sbin/umount.**__type__ helper independently of UID.
 147
 148 Note that _/etc/mtab_ is currently deprecated and *helper=* and other userspace mount options are maintained by *libmount*.
 149
 150 == ENVIRONMENT
 151
 152 *LIBMOUNT_FSTAB*=<path>::
 153 overrides the default location of the _fstab_ file (ignored for *suid*)
 154
 155 *LIBMOUNT_DEBUG*=all::
 156 enables *libmount* debug output
 157
 158 == FILES
 159
 160 _/etc/mtab_::
 161 table of mounted filesystems (deprecated and usually replaced by symlink to _/proc/mounts_)
 162
 163 _/etc/fstab_::
 164 table of known filesystems
 165
 166 _/proc/self/mountinfo_::
 167 table of mounted filesystems generated by kernel.
 168
 169 == HISTORY
 170
 171 A *umount* command appeared in Version 6 AT&T UNIX.
 172
 173 == SEE ALSO
 174
 175 *umount*(2),
 176 *losetup*(8),
 177 *mount_namespaces*(7),
 178 *mount*(8)
 179
 180 include::man-common/bugreports.adoc[]
 181
 182 include::man-common/footer.adoc[]
 183
 184 ifdef::translation[]
 185 include::man-common/translation.adoc[]
 186 endif::[]