Linux.com: CLI Magic: John the Ripper Jul 12, 2005, 07 :00 UTC (8 Talkback[s]) (12057 reads) (Other stories by Joe Barr)
"There is more to the CLI than a collection of operating system commands. There are many tools--applications written without a thought as to the operating system--available at the CLI to handle a wide range of chores. Like cracking passwords, for example. Not for nefarious purposes, you understand: but for education. If you've ever wondered just how secure your passwords are, John the Ripper is a good way to find out. A much nicer way to find out than having a script-kiddy crack it [in] seconds.
"John the Ripper is part of the Openwall GNU/*/Linux project, or Owl for short. It's been around for years, and has been ported to Windows, DOS, BeOS, and quite a few flavors of Unix. If it's not available as a binary for your distribution, download the source code for the latest version from the website and build it yourself..."
