unmount a file systems

umount    [-dflnrv] dir | device […]
umount -a [-dflnrv] [-t vfstype] [-O options]
umount [-hV]

Detaches the file system(s) from the file hierarchy.
dir is the directory where the file system is mounted ( aka mount point).
-i Don't call the /sbin/umount.filesystem helper.
-a All file systems in /etc/mtab are unmounted except /proc
-t [no]vfstype[,…] type of filesystem(s) which will be [not]unmounted.
Examples are: nfs
-O [no]options[,…] only file systems [not]with the specified options in /etc/fstab are effected.
Examples are: rw, ro, auto, noauto
-l Lazy unmount. Detach filesystem now(preventing new opens) and cleanup when last close frees the file system.
-r remount read-only if unmount fails, (This prevents new opens for update or outut)
-f Force unmount (in case of an unreachable NFS system).
-n Unmount without updating /etc/mtab.
-d if the unmounted device was a loop device, free this loop device.
-h help
-V version
-v Verbose

Filesystems cannot be unmounted when 'busy' - ie. when any process's current working directory is there, have files are open on it or when it contains an active swap file.
A -l may be allow the filesystem to be eventually unmounted.

Loop device will be freed if associated with the mount, when loop=... in /etc/mtab, or when -d was given. Any pending loop devices can be freed using losetup -d, see losetup

The syntax of external umount helpers is:
/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) may be used when non-root user wants to umount a mountpoint which is not defined in /etc/fstab (e.g devices mounted by HAL).


/etc/mtab table of mounted file systems

See AlSO

umount(2), mount, losetup(8).