live, dead

© November 2003 Tony Lawrence

Live data is "real" data, sometimes meaning data you can't screw up. "We'll test against live data" vs. "I don't dare test that against live data!".

A dead machine is a non-functional machine: it is crashed, and may be unable to come back up. A "live" machine usually just means it is responding to pings or is obviously "on the network". The intermediate state: running but not on the network, isn't live or dead. It may be "down", and that is also used when the actual state is unknown: you can't see it on the network, so it is "down". It may actually be running fine, and something else is causing you not to see it, but it is still "down" to you until you learn something different. "System down" might be just a specific (but important) application, or it might be the whole machine.

A zombie process is one that shows up as "defunct" in the process table. It isn't really a process at this point; it's nothing more than a slot in the process table and an exit value that nobody bothered to pick up. This comes from creating a process (by forking) and then exiting without waiting for it to finish. When it finally does finish, it becomes a zombie. You can't "kill" a zombie because there's nothing to kill. Init will eventually pick up the exit value and get rid of the process slot.

A zombie machine is one controlled by some program: the implication is that the machine has been hacked and is doing someone else's bidding.

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