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  49 also work, but is obsolete, mainly because it will fail in case this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.
  59 .SH OPTIONS
  60 .TP
  61 .BR \-a , " \-\-all"
  62 All of the filesystems described in
  63 .I /proc/self/mountinfo
  64 (or in deprecated /etc/mtab)
  65 are unmounted, except the proc, devfs, devpts, sysfs, rpc_pipefs and nfsd
  66 filesystems. This list of the filesystems may be replaced by \fB\-\-types\fR
  67 umount option.
  68 .TP
  69 .BR \-A , " \-\-all\-targets"
  70 Unmount all mountpoints in the current namespace for the specified filesystem.
  71 The filesystem can be specified by one of the mountpoints or the device name (or
  72 UUID, etc.).  When this option is used together with \fB\-\-recursive\fR, then
  73 all nested mounts within the filesystem are recursively unmounted.
  74 This option is only supported on systems where /etc/mtab is a symlink
  75 to /proc/mounts.
  76 .TP
  77 .BR \-c , " \-\-no\-canonicalize"
  78 Do not canonicalize paths.  The paths canonicalization is based on
  79 .BR stat (2)
  80 and
  81 .BR readlink (2)
  82 system calls. These system calls may hang in some cases (for example on NFS if
  83 server is not available). The option has to be used with canonical path to the
  84 mount point.
  85
  86 For more details about this option see the
  87 .BR mount (8)
  88 man page. Note that \fBumount\fR does not pass this option to the
  89 .BI /sbin/umount. type
  90 helpers.
  91 .TP
  92 .BR \-d , " \-\-detach\-loop"
  93 When the unmounted device was a loop device, also free this loop
  94 device. This option is unnecessary for devices initialized by
  95 .BR mount (8),
  96 in this case "autoclear" functionality is enabled by default.
  97 .TP
  98 .B \-\-fake
  99 Causes everything to be done except for the actual system call or umount helper
 100 execution; this 'fakes' unmounting the filesystem.  It can be used to remove
 101 entries from the deprecated
 102 .I /etc/mtab
 103 that were unmounted earlier with the
 104 .B \-n
 105 option.
 106 .TP
 107 .BR \-f , " \-\-force"
 108 Force an unmount (in case of an unreachable NFS system).  (Requires kernel
 109 2.1.116 or later.)
 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.  (Requires kernel 2.4.11 or later.)
 123 .TP
 124 .BR \-n , " \-\-no\-mtab"
 125 Unmount without writing in
 126 .IR /etc/mtab .
 127 .TP
 128 .BR \-O , " \-\-test\-opts " \fIoption\fR...
 129 Unmount only the filesystems that have the specified option set in
 130 .IR /etc/fstab .
 131 More than one option may be specified in a comma-separated list.
 132 Each option can be prefixed with
 133 .B no
 134 to indicate that no action should be taken for this option.
 135 .TP
 136 .BR \-R , " \-\-recursive"
 137 Recursively unmount each specified directory.  Recursion for each directory will
 138 stop if any unmount operation in the chain fails for any reason.  The relationship
 139 between mountpoints is determined by /proc/self/mountinfo entries.  The filesystem
 140 must be specified by mountpoint path; a recursive unmount by device name (or UUID)
 141 is unsupported.
 142 .TP
 143 .BR \-r , " \-\-read\-only"
 144 When an unmount fails, try to remount the filesystem read-only.
 145 .TP
 146 .BR \-t , " \-\-types " \fItype\fR...
 147 Indicate that the actions should only be taken on filesystems of the
 148 specified
 149 .IR type .
 150 More than one type may be specified in a comma-separated list.  The list
 151 of filesystem types can be prefixed with
 152 .B no
 153 to indicate that no action should be taken for all of the mentioned types.
 154 .BR
 155 Note that
 156 .B umount
 157 reads information about mounted filesystems from kernel (/proc/mounts) and
 158 filesystem names may be different than filesystem names used in the /etc/fstab
 159 (e.g. "nfs4" vs. "nfs").
 160 .TP
 161 .BR \-v , " \-\-verbose"
 162 Verbose mode.
 163 .TP
 164 .BR \-V , " \-\-version"
 165 Display version information and exit.
 166 .TP
 167 .BR \-h , " \-\-help"
 168 Display help text and exit.
 169 .SH "LOOP DEVICE"
 170 The
 171 .B umount
 172 command will automatically detach loop device previously initialized by
 173 .BR mount (8)
 174 command independently of /etc/mtab.
 175
 176 In this case the device is initialized with "autoclear" flag (see
 177 .BR losetup (8)
 178 output for more details), otherwise it's necessary to use the option \fB \-\-detach\-loop\fR
 179 or call \fBlosetup -d <device>\fR. The autoclear feature is supported since Linux 2.6.25.
 180 .SH EXTERNAL HELPERS
 181 The syntax of external unmount helpers is:
 182 .PP
 183 .RS
 184 .BI umount. suffix
 185 .RI { directory | device }
 186 .RB [ \-flnrv ]
 187 .RB [ \-t
 188 .IR type . subtype ]
 189 .RE
 190 .PP
 191 where \fIsuffix\fR is the filesystem type (or the value from a
 192 \fBuhelper=\fR or \fBhelper=\fR marker in the mtab file).
 193 The \fB\-t\fR option can be used for filesystems that
 194 have subtype support.  For example:
 195 .PP
 196 .RS
 197 .B umount.fuse \-t fuse.sshfs
 198 .RE
 199 .PP
 200 A \fBuhelper=\fIsomething\fR marker (unprivileged helper) can appear in
 201 the \fI/etc/mtab\fR file when ordinary users need to be able to unmount
 202 a mountpoint that is not defined in \fI/etc/fstab\fR
 203 (for example for a device that was mounted by \fBudisks\fR(1)).
 204 .PP
 205 A \fBhelper=\fItype\fR marker in the mtab file will redirect
 206 all unmount requests
 207 to the \fB/sbin/umount.\fItype\fR helper independently of UID.
 208 .PP
 209 Note that \fI/etc/mtab\fR is currently deprecated and helper= and another
 210 userspace mount options are maintained by libmount.
 211 .SH FILES
 212 .TP
 213 .I /etc/mtab
 214 table of mounted filesystems (deprecated and usually replaced by
 215 symlink to /proc/mounts)
 216 .TP
 217 .I /etc/fstab
 218 table of known filesystems
 219 .TP
 220 .I /proc/self/mountinfo
 221 table of mounted filesystems generated by kernel.
 222 .SH ENVIRONMENT
 223 .IP LIBMOUNT_FSTAB=<path>
 224 overrides the default location of the fstab file (ignored for suid)
 225 .IP LIBMOUNT_MTAB=<path>
 226 overrides the default location of the mtab file (ignored for suid)
 227 .IP LIBMOUNT_DEBUG=all
 228 enables libmount debug output
 229 .SH "SEE ALSO"
 230 .BR umount (2),
 231 .BR losetup (8),
 232 .BR mount (8)
 233 .SH HISTORY
 234 A
 235 .B umount
 236 command appeared in Version 6 AT&T UNIX.
 237 .SH AVAILABILITY
 238 The umount command is part of the util-linux package and is available from
 239 .UR https://\:www.kernel.org\:/pub\:/linux\:/utils\:/util-linux/
 240 Linux Kernel Archive
 241 .UE .