Zombies, Daemons, and nobody

Anyone vaguely geeky would probably be able to predict from this title, exactly what I'm going to talk about. However, none of you are so here is a picture:

Yes, I know, it's a little bit dusty,
but I don't really do dusting, I'm afraid.

The above mentioned entities are all to be found in the box pictured above, and in similar boxes everywhere. At least as long as they're running Unix, Linux, or Mac's OS X. I'm not sure about Windows.

Zombies
All the work in your computer is done by processes, which in turn are made up of threads. And you thought that it was little goblins, or hamsters. These processes are created ("spawned"), using an asexual form of reproduction known as "forking". Be careful how you say that.

A process therefore has a single parent, though it can be made into an orphan, which doesn't necessarily involve the parent dying - it's more like being disinherited. Often this happens when processes are "daemonised" (see below).

Child processes usually die, kill themselves or are killed, before their parents. If their parents are on the computer's "Next of Kin" list, they will be informed of such events. The dead process becomes a zombie. Zombies don't actually do anything - they don't get any computer time, and they don't take up an awful lot of memory. They just hang around until the parent does something.


Users can type "kill" to kill a process on the system. This sends a message to the process telling it to die. If it refuses, you need to "kill -9", which tells the system to kill it anyway. It has been suggested that a game like Doom could be used as a fun way to do this...

Daemons

Daemons are programs which are constantly running (as processes) in your computer, waiting for something to happen. They usually provide a service, such as the "CUPS" daemon on this linux system. This sadly does not serve out alcoholic beverages or hold up breasts - it provides printing services to the web browser, word processor, etc. The "HAL" daemon has little in common with the rogue computer in 2001, and it notices when you plug and unplug devices, such as cameras, disks, etc.

daemon is also the name of a non-human user in many computers, since all processes have to be run by a user, even ones that people aren't involved with.

nobody

nobody is a user, too. In some ways it is almost the opposite of root, the all-powerful superuser, who can do anything. nobody is used when someone logs into a publicly accessible system such as a fileserver without having any access rights.

As I write this there are 119 processes in my computer. 2 are running, 117 are sleeping (they've got nothing better to do), and none are zombies. What a crowded place that little box is...