Sometimes you just need a system to be gone immediately. And with immediately I mean NOW. The moment I do something it should be gone.
This comes in quite handy when you work in an environment that offers High Availability, such as an Oracle RAC, and you need to test a failover or a node crash. The same applies to a middle tier that runs the Oracle Application Server on multiple machines.
Well, if you want to do this you can use these handy commands:
[root@mymachine] cd /proc
[root@mymachine] echo c > sysrq-trigger
Of course you must be root to write into that file. And be aware, you must have (physical) access to the machine as you really need to boot it again. This can be done by pressing the button, or if you use virtualization or any ILO-tool by the available interface.