umount <mount path>

[root@sylixos:/root]# help umount         
unmount a volume.
eg. mount /mnt/usb
umount [mount path]
[root@sylixos:/root]# 

[root@sylixos:/root]# umount /mnt/hdd1
[root@sylixos:/root]# showmount
AUTO-Mount point show >>
       VOLUME                    BLK NAME
-------------------- --------------------------------
/media/hdd0          /dev/blk/hdd-0:0                

MTD-Mount point show >>
       VOLUME                    BLK NAME
-------------------- --------------------------------

Mount point show >>
       VOLUME                    BLK NAME
-------------------- --------------------------------
/tmp                 0
[root@sylixos:/root]#