You are probably all too familiar with the situation – you are trying to unmount a drive, but keep getting told by your system that it’s busy. But what application is tying it up? A quick one-liner will tell you:

lsof +D /media/disk1

This will return the command and process ID of any tasks currently accessing the /media/disk1 directory. You can then locate them, or use the kill command to finish them off.