monline

There're obviously a zillion ways to do this. Here's a simple one-liner I've found quite useful:
It starts up instances of dd, each pulling pseudo-random data from /dev/urandom (actually the kernel providing this pseudo-random data creates the CPU load). The number of dd instances is taken from the number of processors reported by /proc/cpuinfo. To stop the extra load, you can easily kill all instances via killall dd (assuming there're no other dd instances running on the server that you've the right/permission to kill and that were not started by this one-liner). And this doesn't even require root access, any user will do. Of course on servers using advanced resource control (eg. cgroups) this won't work since the kernel will limit the total load one user can put on the system (regardless of how many processes you start up).