22.Lock ScreenEffect

The lsof command lists down open files and network connections on Linux. Here's how you can use it to your advantage.

Have you ever tried to close your shell or unmount a drive only to get an error that one or more files are in use? Or perhaps you've tried to edit a file only to find it's locked by another program? 

Maybe you're worried that someone has somehow gained unauthorized access to your Linux system. Using a tool called lsof, you can see which files are open, even over network connections.