sys-utils/umount.8

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  25 .TH UMOUNT 8 "July 2014" "util-linux" "System Administration"
  26 .SH NAME
  27 umount \- unmount file systems
  28 .SH SYNOPSIS
  29 .B umount \-a
  30 .RB [ \-dflnrv ]
  31 .RB [ \-t
  32 .IR fstype ]
  33 .RB [ \-O
  34 .IR option ...]
  35 .sp
  36 .B umount
  37 .RB [ \-dflnrv ]
  38 .RI { directory | device }...
  39 .sp
  40 .B umount
  41 .BR \-h | \-V
  42
  43 .SH DESCRIPTION
  44 The
  45 .B umount
  46 command detaches the mentioned file system(s) from the file hierarchy.  A
  47 file system is specified by giving the directory where it has been
  48 mounted.  Giving the special device on which the file system lives may
  49 also work, but is obsolete, mainly because it will fail in case this
  50 device was mounted on more than one directory.
  51 .PP
  52 Note that a file system cannot be unmounted when it is 'busy' - for
  53 example, when there are open files on it, or when some process has its
  54 working directory there, or when a swap file on it is in use.  The
  55 offending process could even be
  56 .B umount
  57 itself - it opens libc, and libc in its turn may open for example locale
  58 files.  A lazy unmount avoids this problem, but it may introduce another
  59 issues. See \fB\-\-lazy\fR description bellow.
  60 .SH OPTIONS
  61 .TP
  62 .BR \-a , " \-\-all"
  63 All of the filesystems described in
  64 .I /proc/self/mountinfo
  65 (or in deprecated /etc/mtab)
  66 are unmounted, except the proc, devfs, devpts, sysfs, rpc_pipefs and nfsd
  67 filesystems. This list of the filesystems may be replaced by \fB\-\-types\fR
  68 umount option.
  69 .TP
  70 .BR \-A , " \-\-all\-targets"
  71 Unmount all mountpoints in the current namespace for the specified filesystem.
  72 The filesystem can be specified by one of the mountpoints or the device name (or
  73 UUID, etc.).  When this option is used together with \fB\-\-recursive\fR, then
  74 all nested mounts within the filesystem are recursively unmounted.
  75 This option is only supported on systems where /etc/mtab is a symlink
  76 to /proc/mounts.
  77 .TP
  78 .BR \-c , " \-\-no\-canonicalize"
  79 Do not canonicalize paths.  The paths canonicalization is based on
  80 .BR stat (2)
  81 and
  82 .BR readlink (2)
  83 system calls. These system calls may hang in some cases (for example on NFS if
  84 server is not available). The option has to be used with canonical path to the
  85 mount point.
  86
  87 For more details about this option see the
  88 .BR mount (8)
  89 man page. Note that \fBumount\fR does not pass this option to the
  90 .BI /sbin/umount. type
  91 helpers.
  92 .TP
  93 .BR \-d , " \-\-detach\-loop"
  94 When the unmounted device was a loop device, also free this loop
  95 device. This option is unnecessary for devices initialized by
  96 .BR mount (8),
  97 in this case "autoclear" functionality is enabled by default.
  98 .TP
  99 .B \-\-fake
 100 Causes everything to be done except for the actual system call or umount helper
 101 execution; this 'fakes' unmounting the filesystem.  It can be used to remove
 102 entries from the deprecated
 103 .I /etc/mtab
 104 that were unmounted earlier with the
 105 .B \-n
 106 option.
 107 .TP
 108 .BR \-f , " \-\-force"
 109 Force an unmount (in case of an unreachable NFS system).
 110
 111 Note that this option does not guarantee that umount command does not hang.
 112 It's strongly recommended to use absolute paths without symlinks to avoid
 113 unwanted readlink and stat system calls on unreachable NFS in umount.
 114 .TP
 115 .BR \-i , " \-\-internal\-only"
 116 Do not call the \fB/sbin/umount.\fIfilesystem\fR helper even if it exists.
 117 By default such a helper program is called if it exists.
 118 .TP
 119 .BR \-l , " \-\-lazy"
 120 Lazy unmount.  Detach the filesystem from the file hierarchy now,
 121 and clean up all references to this filesystem as soon as it is not busy
 122 anymore.
 123
 124 A system reboot would be expected in near future if you're going to use this
 125 option for network filesystem or local filesystem with submounts.  The
 126 recommended use-case for \fBumount -l\fR is to prevent hangs on shutdown due to
 127 an unreachable network share where a normal umount will hang due to a downed
 128 server or a network partition. Remounts of the share will not be possible.
 129
 130 .TP
 131 .BR \-n , " \-\-no\-mtab"
 132 Unmount without writing in
 133 .IR /etc/mtab .
 134 .TP
 135 .BR \-O , " \-\-test\-opts " \fIoption\fR...
 136 Unmount only the filesystems that have the specified option set in
 137 .IR /etc/fstab .
 138 More than one option may be specified in a comma-separated list.
 139 Each option can be prefixed with
 140 .B no
 141 to indicate that no action should be taken for this option.
 142 .TP
 143 .BR \-R , " \-\-recursive"
 144 Recursively unmount each specified directory.  Recursion for each directory will
 145 stop if any unmount operation in the chain fails for any reason.  The relationship
 146 between mountpoints is determined by /proc/self/mountinfo entries.  The filesystem
 147 must be specified by mountpoint path; a recursive unmount by device name (or UUID)
 148 is unsupported.
 149 .TP
 150 .BR \-r , " \-\-read\-only"
 151 When an unmount fails, try to remount the filesystem read-only.
 152 .TP
 153 .BR \-t , " \-\-types " \fItype\fR...
 154 Indicate that the actions should only be taken on filesystems of the
 155 specified
 156 .IR type .
 157 More than one type may be specified in a comma-separated list.  The list
 158 of filesystem types can be prefixed with
 159 .B no
 160 to indicate that no action should be taken for all of the mentioned types.
 161 .BR
 162 Note that
 163 .B umount
 164 reads information about mounted filesystems from kernel (/proc/mounts) and
 165 filesystem names may be different than filesystem names used in the /etc/fstab
 166 (e.g. "nfs4" vs. "nfs").
 167 .TP
 168 .BR \-v , " \-\-verbose"
 169 Verbose mode.
 170 .TP
 171 .BR \-V , " \-\-version"
 172 Display version information and exit.
 173 .TP
 174 .BR \-h , " \-\-help"
 175 Display help text and exit.
 176 .SH "LOOP DEVICE"
 177 The
 178 .B umount
 179 command will automatically detach loop device previously initialized by
 180 .BR mount (8)
 181 command independently of /etc/mtab.
 182
 183 In this case the device is initialized with "autoclear" flag (see
 184 .BR losetup (8)
 185 output for more details), otherwise it's necessary to use the option \fB \-\-detach\-loop\fR
 186 or call \fBlosetup -d <device>\fR. The autoclear feature is supported since Linux 2.6.25.
 187 .SH EXTERNAL HELPERS
 188 The syntax of external unmount helpers is:
 189 .PP
 190 .RS
 191 .BI umount. suffix
 192 .RI { directory | device }
 193 .RB [ \-flnrv ]
 194 .RB [ \-t
 195 .IR type . subtype ]
 196 .RE
 197 .PP
 198 where \fIsuffix\fR is the filesystem type (or the value from a
 199 \fBuhelper=\fR or \fBhelper=\fR marker in the mtab file).
 200 The \fB\-t\fR option can be used for filesystems that
 201 have subtype support.  For example:
 202 .PP
 203 .RS
 204 .B umount.fuse \-t fuse.sshfs
 205 .RE
 206 .PP
 207 A \fBuhelper=\fIsomething\fR marker (unprivileged helper) can appear in
 208 the \fI/etc/mtab\fR file when ordinary users need to be able to unmount
 209 a mountpoint that is not defined in \fI/etc/fstab\fR
 210 (for example for a device that was mounted by \fBudisks\fR(1)).
 211 .PP
 212 A \fBhelper=\fItype\fR marker in the mtab file will redirect
 213 all unmount requests
 214 to the \fB/sbin/umount.\fItype\fR helper independently of UID.
 215 .PP
 216 Note that \fI/etc/mtab\fR is currently deprecated and helper= and another
 217 userspace mount options are maintained by libmount.
 218 .SH FILES
 219 .TP
 220 .I /etc/mtab
 221 table of mounted filesystems (deprecated and usually replaced by
 222 symlink to /proc/mounts)
 223 .TP
 224 .I /etc/fstab
 225 table of known filesystems
 226 .TP
 227 .I /proc/self/mountinfo
 228 table of mounted filesystems generated by kernel.
 229 .SH ENVIRONMENT
 230 .IP LIBMOUNT_FSTAB=<path>
 231 overrides the default location of the fstab file (ignored for suid)
 232 .IP LIBMOUNT_MTAB=<path>
 233 overrides the default location of the mtab file (ignored for suid)
 234 .IP LIBMOUNT_DEBUG=all
 235 enables libmount debug output
 236 .SH "SEE ALSO"
 237 .BR umount (2),
 238 .BR losetup (8),
 239 .BR mount (8)
 240 .SH HISTORY
 241 A
 242 .B umount
 243 command appeared in Version 6 AT&T UNIX.
 244 .SH AVAILABILITY
 245 The umount command is part of the util-linux package and is available from
 246 .UR https://\:www.kernel.org\:/pub\:/linux\:/utils\:/util-linux/
 247 Linux Kernel Archive
 248 .UE .