Well I run into this issue a lot. I cannot unmount a partition.. or I cannot open a file because it’s locked and in use. How do I see what has that file or mount locked? Well since everything in Linux is a file you can list open files … which will show you what processes have certain files locked this is done with the lsof command.
For example on my Mythbox I want to see what has the /storage partition locked I would issue:
[root@linuxmonkey2 ~]# lsof | grep storage
mysqld 2285 mysql 13u REG 253,0 124 325498 /var/lib/mysql/mythconverg/storagegroup.MYD
mysqld 2285 mysql 57u REG 253,0 5120 325424 /var/lib/mysql/mythconverg/storagegroup.MYI
gnome-key 2887 mythtv mem REG 253,0 40808 502127 /usr/lib/libhal-storage.so.1.0.0
mythbacke 7126 root 18w REG 253,2 1492874876 1523719 /storage/recordings/1007_20100421150000.mpg
From that you can see mysql, gnome-key and mythbackend all have open files inside storage I would have to kill them before unmounting.