John The Ripper, program written by Alexander Peslyak, allows fast cracking of users passwords that can be used by both sides of the security world - crackers and system administrators. As basically all of the Linux/UNIX security books suggest, system administrators should use Crack or John The Ripper for finding local users with weak passwords.
As the patch writer notes: "This patch has been tested on x86 only and does not work yet on big endian systems. It uses asm code for speed but a portable C version is included as well. The asm version checks about 150,000 passwords per second on a 1 GHz system. Password cracking is much easier on OpenVMS than on other systems since passwords are not case sensitive and limited to alphanumeric, '$' and '_' only."