Linux Amazing Keypresses & Commands : Set 3

1. Unmount busy drives
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 /mnt/windows
This will return the command and process ID of any tasks currently accessing the /mnt/windows directory. You can then locate them, or use the kill command to finish them off.

2. su command  fast execution without logging in.
$su --c [command]
It enables you to issue a command in administrative mode directly after providing the superuser password. And when the command is executed the user is logged off to the previous user.