“This article will deal with John from a system administrator’s
perspective, so we expect you to have intermediate knowledge about
your Linux system, whatever distribution that may be, and that you
are a security-conscious person with basic security knowledge.
However, this article might appeal to you also if you are a home
user wanting to learn about these kind of things, but be warned:
some of the commands presented below will ask a great deal of your
CPU time, so maybe it would be better if you had a test machine
and/or lots of time and patience, because password cracking
attempts may take days, even on a relatively new machine.