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  49 also work, but is obsolete, mainly because it will fail in case this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