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  49 also work, but is obsolete, mainly because it will fail in case this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