John The Ripper - Password cracker

John the Ripper is a fast password cracker, currently available for many flavors of Unix, Windows, DOS, BeOS, and OpenVMS.
It's primary purpose is to detect weak Unix passwords.
Besides several crypt(3) password hash types most commonly found on various Unix systems, supported out of the box are Windows LM hashes, plus lots of other hashes and ciphers in the community-enhanced version.
You can download john the ripper from here
Syntax : john [options] [password-files]
--config=FILE : use FILE instead of john.conf
--wordlist[=FILE] --stdin wordlist mode, read words from FILE or stdin
--pipe like --stdin, but bulk reads, and allows rules
--encoding=NAME : input data is non-ascii (eg. UTF-8, ISO-8859-1). For a full list of NAME use --list=encodings
--rules[=SECTION] : enable word mangling rules for wordlist modes
--stdout[=LENGTH] : just output candidate passwords (cut at LENGTH)
--make-charset=FILE : make a charset file. It will be overwritten
--show[=LEFT] : show cracked passwords (if =LEFT, then uncracked)
--test[=TIME] : run tests and benchmarks for TIME seconds each
--users=[-]LOGIN|UID[,..] [do not] load this (these) user(s) only
--format=NAME : force hash type NAME: afs bf bfegg bsdi crc32 crypt des django dmd5 dominosec dragonfly3-32 dragonfly3-64 dragonfly4-32 dragonfly4-64 drupal7 dummy dynamic_n epi episerver gost hdaa hmac-md5 hmac-sha1 hmac-sha224 hmac-sha256 hmac-sha384 hmac-sha512 hmailserver ipb2 keepass keychain krb4 krb5 lm lotus5 md4-gen md5 md5ns mediawiki mscash mscash2 mschapv2 mskrb5 mssql mssql05 mysql mysql-sha1 nethalflm netlm netlmv2 netntlm netntlmv2 nsldap nt nt2 odf office oracle oracle11 osc pdf phpass phps pix-md5 pkzip po pwsafe racf rar raw-md4 raw-md5 raw-md5u raw-sha raw-sha1 raw-sha1-linkedin raw-sha1-ng raw-sha224 raw-sha256 raw-sha384 raw-sha512 salted-sha1 sapb sapg sha1-gen sha256crypt sha512crypt sip ssh sybasease trip vnc wbb3 wpapsk xsha xsha512 zip
--save-memory=LEVEL : enable memory saving, at LEVEL 1..3
--nolog : disables creation and writing to john.log file
--max-run-time=N : gracefully exit after this many seconds
--plugin=NAME[,..] : load this (these) dynamic plugin(s)
For more information type : john

If you have a problem or you need some explanations just write under this post!