umount -- unmount file systems

     umount [-fNnv] special ... | node ... | fsid ...
     umount -a | -A [-F fstab] [-fnv] [-h host] [-t type]

     The umount utility calls the unmount(2) system call to remove a file sys-
     tem from the file system tree.  The file system can be specified by its
     special device or remote node (rhost:path), the path to the mount point
     node or by the file system ID fsid as reported by ``mount -v'' when run
     by root.

     The options are as follows:

     -a      All the file systems described in fstab(5) are unmounted.

     -A      All the currently mounted file systems except the root are

     -F fstab
             Specify the fstab file to use.

     -f      The file system is forcibly unmounted.  Active special devices
             continue to work, but all other files return errors if further
             accesses are attempted.  The root file system cannot be forcibly
             unmounted.  For NFS, a forced dismount can take up to 1 minute or
             more to complete against an unresponsive server and may throw
             away data not yet written to the server for this case.  If a
             process, such as umount without the -f flag is hung on an NFS
             mount point, use the -N flag instead.  Also, doing a forced dis-
             mount of an NFSv3 mount when rpc.lockd(8) is running is unsafe
             and can result in a crash.

     -h host
             Only file systems mounted from the specified host will be
             unmounted.  This option implies the -A option and, unless other-
             wise specified with the -t option, will only unmount NFS file

     -N      Do a forced dismount of an NFS mount point without checking the
             mount path.  This option can only be used with the path to the
             mount point node and the path must be specified exactly as it was
             at mount time.  This option is useful when a process is hung
             waiting for an unresponsive NFS server while holding a vnode lock
             on the mounted-on vnode, such that umount with the -f flag can't
             complete.  Using this option can result in a loss of file updates
             that have not been flushed to the NFS server.

     -n      Unless the -f is used, the umount will not unmount an active file
             system.  It will, however, perform a flush.  This flag disables
             this behaviour, preventing the flush if there are any files open.

     -t type
             Is used to indicate the actions should only be taken on file sys-
             tems 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 for which
             action should not be taken.  For example, the umount command:

                   umount -a -t nfs,nullfs

             unmounts all file systems of the type NFS and NULLFS that are
             listed in the fstab(5) file.

     -v      Verbose, additional information is printed out as each file sys-
             tem is unmounted.

     PATH_FSTAB  If the environment variable PATH_FSTAB is set, all operations
                 are performed against the specified file.  PATH_FSTAB will
                 not be honored if the process environment or memory address
                 space is considered ``tainted''.  (See issetugid(2) for more

     /etc/fstab  file system table

     unmount(2), fstab(5), autounmountd(8), mount(8)

     A umount utility appeared in Version 6 AT&T UNIX.