Sounds scary, doesn't it? "zombie" is the rather macabre name given by early unix developers to a process which has terminated (either because it was killed or because it chose to exit() on its own), but whose parent process has not yet been notified of its termination. This is the kind of unix idiosyncrasy that might be termed "cute."

Normally, as with other unkillable conditions, this one exists only for an invisible instant, and is resolved. However, when said parent process neglects to call wait() (how a parent is notified about child exits - go figure), or becomes in some other way indisposed, zombie children can start to pile up.

Fortunately, while people bug out because they can't kill it, it is, in fact, already dead - hence the name. Zombies exist only as entries in the process table - they consume no resources, and are there solely as a holder for the child's exit status until the parent retrieves it. They're generally not as bad as people think they are; although they are sometimes evidence of bad programming, and process tables are of finite size, and so can fill up too...

Zombies can be observed via ps as processes with a status of Z.

If they're really burning your goat, you can attempt to kill the parent process. Parents can be determined via

ps -fauwxw

, and killed separately.

If a process seems to have no parent but is nonetheless a zombie, well, that's weird, but you can try a

kill -s SIGHUP 1

... that might jolt the init process into doing housekeeping.

After that, if you're still stuck with it, it's time to reboot. And barricade yourself in the house.

See also: oprhan process

In Haiti, where the voudun religion and mythos developed, legend has it that a bokor ("sorcerer") has the power to raise and command the dead. The necromantic slave is referred to as zombi.

Apparently, the American government was researching the process by which a bokor can raise a zombie. The bokor, with a generational knowledge of Haiti's herbal resources, can collect spores, seeds, and other sources of natural chemicals that can be used to brew up a "magical" powder. This powder, when applied to a human being, reduces that person to a near-death state.

Haiti's tropical climate and limited access to medical technology makes it imperative that the dead are buried as quickly as possible, to prevent the spread of dangerous diseases. That means that they don't bother with embalming or autopsy — they check for vital signs, and if they can't find any, they toss them into a hastily-built wooden coffin and bury them.

Of course, when in a bokor-induced torpor, one's vital signs become very faint and difficult to detect. As a result, if you have been subjected to a bokor's mischief, you may be buried alive. The bokor, of course, is well aware of this, and will dig out his zombie prize after the death certificate has been issued and final rites administered.

Of course, by the time the bokor deigns to deliver you from your living tomb, you may be suffering from severe oxygen deprivation. In a box barely big enough to fit you, you will quickly run out of air. Depending on how long the bokkor decides to wait, this may leave you with a significant degree of brain damage — and therefore, you would be the perfect slave: too stupid to escape, but still able to move around, lift things, do household chores; and as far as anyone knows, you don't exist.

This, of course, is all hearsay and legend....

Noder's Note: For a more specific description of this process, take a look at pimephalis's super writeup zombie, and Gritchka's zombification. (Too late, the latter is gone.)