How can I watch the processes in such level
 

I want to observe how the command "exec" work in the level shown in the video, I mean there is no GUI

I would love to see how exec swaps the ls command with bash


Any idea how to do that? any kernel logs that I can see?


http://www.youtube.com/watch?v=h7v7kqyz7XU

Maybe I don't understand the question, but press [ctrl][alt] + [F1] and you should see a CLI login screen. Actually you can press any of [F1] through [F6] and have multiple CLI sessions running. To get back to the GUI press [ctrl][alt] + [F7].

If this isn't what you mean please do clarify...

exec <command> will replace the current shell, and <command> will be running (in place of your original shell - it does not exist any more, overwritten). When the <program> completed your login will be terminated as well because you replaced your login shell (that happened in that video). ls terminates almost immediately, therefore you will not see the result of the command. You can check it by executing ls > /tmp/ls and check the file /tmp/ls afterward. top will running as long as you wish, after quitting you will be returned to the login prompt again.