Unmounts several file systems at one time. If mount-points are included with the –a option, those file systems are unmounted. If no mount points are included, an attempt is made to unmount all file systems that are listed in /etc/mnttab except for the “required” file systems, such as /, /usr, /var, /proc, /dev/fd, and /tmp. Because the file system is already mounted and should have an entry in /etc/mnttab, you do not need to include a flag for the file system type.
Forces a busy file system to be unmounted. You can use this option to unhang a client that is hung while trying to mount an unmountable file system.
Caution - By forcing an unmount of a file system, you can cause data loss if files are being written to that system.
# umount /usr/manExample 5-2 Using Options with umount
The following example displays the results of running umount –a -V:
# umount -a -V umount /home/kathys umount /opt umount /home umount /net
Note that this command does not actually unmount the file systems.