Ubuntu Manpages

umount.crypt

unmount a dm-crypt encrypted volume

umount.crypt [-n] directory

This option is ignored (originally is "force unmount for NFS").
Do not update /etc/mtab.
Try mounting read-only if unmounting fails. This option is currently not implemented and is ignored.

umount.crypt will unmount directory and disassociates the underlying crypto device, and loop device if such was used.