I have discovered a funny and didactic online game where you can test and improve your hacking skills. The objective of the game is to hack a Linux server and scale user privileges. You start with user level1 and you must exploit several bugs on the system to get access to the highest levelX that you can achieve.
For example you can try the game blowfish that I love (currently I am stuck at level5 )
Telnet to blowfish.smashthestack.org port 6666 to recieve an encrypted passwd. #decrypt it and log in to level2 (If you are too lazy to decrypt it google can help you) ssh firstname.lastname@example.org -p 2222 #follow the hints and try to get access to level13
Your mission is not to get root (but if you do you would win the medal of honor 😉