#Bash 的 umount 命令

UMOUNT(8)                    System Administration                   UMOUNT(8)

NAME
       umount - unmount filesystems

SYNOPSIS
       umount -a [-dflnrv] [-t fstype] [-O option...]

       umount [-dflnrv] {directory|device}

       umount -h|-V

DESCRIPTION
       The umount command detaches the mentioned filesystem(s) from the file
       hierarchy. A filesystem is specified by giving the directory where it
       has been mounted. Giving the special device on which the filesystem
       lives may also work, but is obsolete, mainly because it will fail in
       case this device was mounted on more than one directory.

       Note that a filesystem cannot be unmounted when it is 'busy' - for
       example, when there are open files on it, or when some process has its
       working directory there, or when a swap file on it is in use. The
       offending process could even be umount itself - it opens libc, and libc
       in its turn may open for example locale files. A lazy unmount avoids
       this problem, but it may introduce other issues. See --lazy description
       below.

OPTIONS
       -a, --all
           All of the filesystems described in /proc/self/mountinfo (or in
           deprecated /etc/mtab) are unmounted, except the proc, devfs,
           devpts, sysfs, rpc_pipefs and nfsd filesystems. This list of the
           filesystems may be replaced by --types umount option.

       -A, --all-targets
           Unmount all mountpoints in the current mount namespace for the
           specified filesystem. The filesystem can be specified by one of the
           mountpoints or the device name (or UUID, etc.). When this option is
           used together with --recursive, then all nested mounts within the
           filesystem are recursively unmounted. This option is only supported
           on systems where /etc/mtab is a symlink to /proc/mounts.

       -c, --no-canonicalize
           Do not canonicalize paths. The paths canonicalization is based on
           stat(2) and readlink(2) system calls. These system calls may hang
           in some cases (for example on NFS if server is not available). The
           option has to be used with canonical path to the mount point.

           This option is silently ignored by umount for non-root users.

           For more details about this option see the mount(8) man page. Note
           that umount does not pass this option to the /sbin/umount.type
           helpers.

       -d, --detach-loop
           When the unmounted device was a loop device, also free this loop
           device. This option is unnecessary for devices initialized by
           mount(8), in this case "autoclear" functionality is enabled by
           default.

       --fake
           Causes everything to be done except for the actual system call or
           umount helper execution; this 'fakes' unmounting the filesystem. It
           can be used to remove entries from the deprecated /etc/mtab that
           were unmounted earlier with the -n option.

       -f, --force
           Force an unmount (in case of an unreachable NFS system).

           Note that this option does not guarantee that umount command does
           not hang. It’s strongly recommended to use absolute paths without
           symlinks to avoid unwanted readlink(2) and stat(2) system calls on
           unreachable NFS in umount.

       -i, --internal-only
           Do not call the /sbin/umount.filesystem helper even if it exists.
           By default such a helper program is called if it exists.

       -l, --lazy
           Lazy unmount. Detach the filesystem from the file hierarchy now,
           and clean up all references to this filesystem as soon as it is not
           busy anymore.

           A system reboot would be expected in near future if you’re going to
           use this option for network filesystem or local filesystem with
           submounts. The recommended use-case for umount -l is to prevent
           hangs on shutdown due to an unreachable network share where a
           normal umount will hang due to a downed server or a network
           partition. Remounts of the share will not be possible.

       -N, --namespace ns
           Perform umount in the mount namespace specified by ns. ns is either
           PID of process running in that namespace or special file
           representing that namespace.

           umount switches to the namespace when it reads /etc/fstab, writes
           /etc/mtab (or writes to /run/mount) and calls umount(2) system
           call, otherwise it runs in the original namespace. It means that
           the target mount namespace does not have to contain any libraries
           or other requirements necessary to execute umount(2) command.

           See mount_namespaces(7) for more information.

       -n, --no-mtab
           Unmount without writing in /etc/mtab.

       -O, --test-opts option...
           Unmount only the filesystems that have the specified option set in
           /etc/fstab. More than one option may be specified in a
           comma-separated list. Each option can be prefixed with no to
           indicate that no action should be taken for this option.

       -q, --quiet
           Suppress "not mounted" error messages.

       -R, --recursive
           Recursively unmount each specified directory. Recursion for each
           directory will stop if any unmount operation in the chain fails for
           any reason. The relationship between mountpoints is determined by
           /proc/self/mountinfo entries. The filesystem must be specified by
           mountpoint path; a recursive unmount by device name (or UUID) is
           unsupported. Since version 2.37 it umounts also all over-mounted
           filesystems (more filesystems on the same mountpoint).

       -r, --read-only
           When an unmount fails, try to remount the filesystem read-only.

       -t, --types type...
           Indicate that the actions should only be taken on filesystems of
           the specified type. More than one type may be specified in a
           comma-separated list. The list of filesystem types can be prefixed
           with no to indicate that no action should be taken for all of the
           mentioned types. Note that umount reads information about mounted
           filesystems from kernel (/proc/mounts) and filesystem names may be
           different than filesystem names used in the /etc/fstab (e.g.,
           "nfs4" vs. "nfs").

       -v, --verbose
           Verbose mode.

       -h, --help
           Display help text and exit.

       -V, --version
           Print version and exit.

NON-SUPERUSER UMOUNTS
       Normally, only the superuser can umount filesystems. However, when
       fstab contains the user option on a line, anybody can umount the
       corresponding filesystem. For more details see mount(8) man page.

       Since version 2.34 the umount command can be used to perform umount
       operation also for fuse filesystems if kernel mount table contains
       user’s ID. In this case fstab user= mount option is not required.

       Since version 2.35 umount command does not exit when user permissions
       are inadequate by internal libmount security rules. It drops suid
       permissions and continue as regular non-root user. This can be used to
       support use-cases where root permissions are not necessary (e.g., fuse
       filesystems, user namespaces, etc).

LOOP DEVICE
       The umount command will automatically detach loop device previously
       initialized by mount(8) command independently of /etc/mtab.

       In this case the device is initialized with "autoclear" flag (see
       losetup(8) output for more details), otherwise it’s necessary to use
       the option --detach-loop or call losetup -d device. The autoclear
       feature is supported since Linux 2.6.25.

EXTERNAL HELPERS
       The syntax of external unmount helpers is:

          umount.suffix {directory|device} [-flnrv] [-N namespace] [-t
          type.subtype]

       where suffix is the filesystem type (or the value from a uhelper= or
       helper= marker in the mtab file). The -t option can be used for
       filesystems that have subtype support. For example:

          umount.fuse -t fuse.sshfs

       A uhelper=something marker (unprivileged helper) can appear in the
       /etc/mtab file when ordinary users need to be able to unmount a
       mountpoint that is not defined in /etc/fstab (for example for a device
       that was mounted by udisks(1)).

       A helper=type marker in the mtab file will redirect all unmount
       requests to the /sbin/umount.type helper independently of UID.

       Note that /etc/mtab is currently deprecated and helper= and other
       userspace mount options are maintained by libmount.

ENVIRONMENT
       LIBMOUNT_FSTAB=<path>
           overrides the default location of the fstab file (ignored for suid)

       LIBMOUNT_DEBUG=all
           enables libmount debug output

FILES
       /etc/mtab
           table of mounted filesystems (deprecated and usually replaced by
           symlink to /proc/mounts)

       /etc/fstab
           table of known filesystems

       /proc/self/mountinfo
           table of mounted filesystems generated by kernel.

HISTORY
       A umount command appeared in Version 6 AT&T UNIX.

SEE ALSO
       umount(2), losetup(8), mount_namespaces(7), mount(8)

REPORTING BUGS
       For bug reports, use the issue tracker at
       https://github.com/util-linux/util-linux/issues.

AVAILABILITY
       The umount command is part of the util-linux package which can be
       downloaded from Linux Kernel Archive
       <https://www.kernel.org/pub/linux/utils/util-linux/>.

util-linux 2.39.3                 2023-11-21                         UMOUNT(8)