s6-linux-utils
Software
skarnet.org
 The s6-umount program 
 s6-umount unmounts filesystems.
 Interface 
     s6-umount [ -a | mntpoint ]
 -  s6-umount -a unmounts all partitions according to /proc/mounts. 
-  If the -a option is not given,
s6-umount unmounts the filesystem mounted on mntpoint. 
-  s6-umount does not touch /etc/mtab.