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  49 also work, but is obsolete, mainly because it will fail in case this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 below.
  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 , " \-\-namespace " \fIns
 132 Perform umount in namespace specified by \fIns\fR.
 133 \fIns\fR is either PID of process running in that namespace
 134 or special file representing that namespace.
 135 .sp
 136 .BR umount (8)
 137 switches to the namespace when it reads /etc/fstab, writes /etc/mtab (or writes to /run/mount) and calls
 138 .BR umount (2)
 139 system call, otherwise it runs in the original namespace. It means that the target namespace does not have
 140 to contain any libraries or another requirements necessary to execute
 141 .BR umount (2)
 142 command.
 143 .sp
 144 See \fBnamespaces\fR(7) for more information.
 145 .TP
 146 .BR \-n , " \-\-no\-mtab"
 147 Unmount without writing in
 148 .IR /etc/mtab .
 149 .TP
 150 .BR \-O , " \-\-test\-opts " \fIoption\fR...
 151 Unmount only the filesystems that have the specified option set in
 152 .IR /etc/fstab .
 153 More than one option may be specified in a comma-separated list.
 154 Each option can be prefixed with
 155 .B no
 156 to indicate that no action should be taken for this option.
 157 .TP
 158 .BR \-q , " \-\-quiet"
 159 Suppress "not mounted" error messages.
 160 .TP
 161 .BR \-R , " \-\-recursive"
 162 Recursively unmount each specified directory.  Recursion for each directory will
 163 stop if any unmount operation in the chain fails for any reason.  The relationship
 164 between mountpoints is determined by /proc/self/mountinfo entries.  The filesystem
 165 must be specified by mountpoint path; a recursive unmount by device name (or UUID)
 166 is unsupported.
 167 .TP
 168 .BR \-r , " \-\-read\-only"
 169 When an unmount fails, try to remount the filesystem read-only.
 170 .TP
 171 .BR \-t , " \-\-types " \fItype\fR...
 172 Indicate that the actions should only be taken on filesystems of the
 173 specified
 174 .IR type .
 175 More than one type may be specified in a comma-separated list.  The list
 176 of filesystem types can be prefixed with
 177 .B no
 178 to indicate that no action should be taken for all of the mentioned types.
 179 Note that
 180 .B umount
 181 reads information about mounted filesystems from kernel (/proc/mounts) and
 182 filesystem names may be different than filesystem names used in the /etc/fstab
 183 (e.g., "nfs4" vs. "nfs").
 184 .TP
 185 .BR \-v , " \-\-verbose"
 186 Verbose mode.
 187 .TP
 188 .BR \-V , " \-\-version"
 189 Display version information and exit.
 190 .TP
 191 .BR \-h , " \-\-help"
 192 Display help text and exit.
 193 .SH NON-SUPERUSER UMOUNTS
 194 Normally, only the superuser can umount filesystems.
 195 However, when
 196 .I fstab
 197 contains the
 198 .B user
 199 option on a line, anybody can umount the corresponding filesystem.  For more details see
 200 .BR mount (8)
 201 man page.
 202 .PP
 203 Since version 2.34 \fBumount\fR command allows to perform umount operation also
 204 for fuse filesystems if kernel mount table contains user's ID.  In this case fstab
 205 user= mount option is not required.
 206 .PP
 207 Since version 2.35 \fBumount\fR command does not exit when user permissions are
 208 inadequate by internal libmount security rules.  It drops suid permissions
 209 and continue as regular non-root user. It allows to support use-cases where
 210 root permissions are not necessary (e.g., fuse filesystems, user namespaces,
 211 etc).
 212 .SH LOOP DEVICE
 213 The
 214 .B umount
 215 command will automatically detach loop device previously initialized by
 216 .BR mount (8)
 217 command independently of /etc/mtab.
 218
 219 In this case the device is initialized with "autoclear" flag (see
 220 .BR losetup (8)
 221 output for more details), otherwise it's necessary to use the option \fB \-\-detach\-loop\fR
 222 or call \fBlosetup \-d <device>\fR. The autoclear feature is supported since Linux 2.6.25.
 223 .SH EXTERNAL HELPERS
 224 The syntax of external unmount helpers is:
 225 .PP
 226 .RS
 227 .BI umount. suffix
 228 .RI { directory | device }
 229 .RB [ \-flnrv ]
 230 .RB [ \-N
 231 .IR namespace ]
 232 .RB [ \-t
 233 .IR type . subtype ]
 234 .RE
 235 .PP
 236 where \fIsuffix\fR is the filesystem type (or the value from a
 237 \fBuhelper=\fR or \fBhelper=\fR marker in the mtab file).
 238 The \fB\-t\fR option can be used for filesystems that
 239 have subtype support.  For example:
 240 .PP
 241 .RS
 242 .B umount.fuse \-t fuse.sshfs
 243 .RE
 244 .PP
 245 A \fBuhelper=\fIsomething\fR marker (unprivileged helper) can appear in
 246 the \fI/etc/mtab\fR file when ordinary users need to be able to unmount
 247 a mountpoint that is not defined in \fI/etc/fstab\fR
 248 (for example for a device that was mounted by \fBudisks\fR(1)).
 249 .PP
 250 A \fBhelper=\fItype\fR marker in the mtab file will redirect
 251 all unmount requests
 252 to the \fB/sbin/umount.\fItype\fR helper independently of UID.
 253 .PP
 254 Note that \fI/etc/mtab\fR is currently deprecated and helper= and another
 255 userspace mount options are maintained by libmount.
 256 .SH ENVIRONMENT
 257 .IP LIBMOUNT_FSTAB=<path>
 258 overrides the default location of the fstab file (ignored for suid)
 259 .IP LIBMOUNT_MTAB=<path>
 260 overrides the default location of the mtab file (ignored for suid)
 261 .IP LIBMOUNT_DEBUG=all
 262 enables libmount debug output
 263 .SH FILES
 264 .TP
 265 .I /etc/mtab
 266 table of mounted filesystems (deprecated and usually replaced by
 267 symlink to /proc/mounts)
 268 .TP
 269 .I /etc/fstab
 270 table of known filesystems
 271 .TP
 272 .I /proc/self/mountinfo
 273 table of mounted filesystems generated by kernel.
 274 .SH HISTORY
 275 A
 276 .B umount
 277 command appeared in Version 6 AT&T UNIX.
 278 .SH SEE ALSO
 279 .BR umount (2),
 280 .BR losetup (8),
 281 .BR mount (8)
 282 .SH AVAILABILITY
 283 The umount command is part of the util-linux package and is available from
 284 .UR https://\:www.kernel.org\:/pub\:/linux\:/utils\:/util-linux/
 285 Linux Kernel Archive
 286 .UE .