Umount + can't umount

Solution 1:

You can use fuser to see which processes are still using that mount:

fuser -mu /mnt/cdrom

If you want to kill those processes via fuser, use -k:

fuser -mk /mnt/cdrom

I often (as in: I wish I had a nickel every time...) find myself unable to umount because I've cd'd to a mount as myself then su'd to root. My old shell is still on the mount point so I can't umount. Try exiting the root shell and see if your user's shell is still cd'd to something under /mnt/cdrom.

Solution 2:

You need to figure out what is using the tile system in the mount and stop those process. You can get an idea of what might be there by running lsof | grep /mnt/cdrom to see what procses have that folder open. You might start by closing any file managers and cd'ing out of there from any terminals.