stress is a tool which imposes a configurable amount of CPU,
memory, I/O, or disk stress on a POSIX-compliant operating
system. It is written in portable ANSI C, and uses the GNU
Autotools to compile on a great number of UNIX-like operating
systems.

stress is not a benchmark. It is a tool used by system
administrators to evaluate how well their systems will scale,
by kernel programmers to evaluate perceived performance
characteristics, and by systems programmers to expose the
classes of bugs which only or more frequently manifest
themselves when the system is under heavy load.

WWW: http://weather.ou.edu/~apw/projects/stress/