umount -a [-dflnrv] [-t vfstype] [-O options]
umount [-dflnrv] dir | device [...]
Note that a file system 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.
Options for the umount command:
|-V||Print version and exit.|
|-h||Print help message and exit.|
|-n||Unmount without writing in /etc/mtab.|
|-r||In case unmounting fails, try to remount read-only.|
|-d||In case the unmounted device was a loop device, also free this loop device.|
|-i||Dont call the /sbin/umount.<filesystem> helper even if it exists. By default /sbin/umount.<filesystem> helper is called if one exists.|
|-a||All of the file systems described in /etc/mtab are unmounted. (With umount version 2.7 and later: the proc filesystem is not unmounted.)|
|Indicate that the actions should only be taken on file systems of the specified type. More than one type may be specified in a comma separated list. The list of file system types can be prefixed with no to specify the file system types on which no action should be taken.|
|Indicate that the actions should only be taken on file systems with the specified options in /etc/fstab. More than one option type may be specified in a comma separated list. Each option can be prefixed with no to specify options for which no action should be taken.|
|-f||Force unmount (in case of an unreachable NFS system). (Requires kernel 2.1.116 or later.)|
Lazy unmount. Detach the filesystem from the filesystem hierarchy now,
and cleanup all references to the filesystem as soon as it is not busy
(Requires kernel 2.4.11 or later.)
/sbin/umount.<suffix> [-nlfvr] dir | device
where the <suffix> is filesystem type or a value from "uhelper=" mtab option.
The uhelper (unprivileged umount request helper) is possible used when non-root user wants to umount a mountpoint which is not defined in the /etc/fstab file (e.g devices mounted by HAL).