umount : unmount filesystems
[SYNOPSIS] umount OPTION FILESYSTEM
OPTION
-a unmount all filesystems
-A unmount all mountpoints for the given device in the current namespace
-c don't canonicalize paths
-d if mounted loop device, also free this loop device
-f force unmount (in case of an unreachable NFS system)
-d if mounted loop device, also free this loop device
-i don't call the umount.<type> helpers
-n don't write to /etc/mtab
-l detach the filesystem now, clean up things later
-R recursively unmount a target with all its children
-r in case unmounting fails, try to remount read-only
-R recursively unmount a target with all its children
-v say what is being done
-q suppress 'not mounted' error messages