What is a user-id?

Digging through posts I have started and failed to finish, I found a sub-thread I started on the Fedora list, trying to explain the difference between a system user, as represented by a user-id, and the human whose hands are on the keyboard:

http://lists.fedoraproject.org/pipermail/users/2012-April/416380.html

When you hear/see the word "user" it's only natural to think in terms of a human user. So, when you think of a user-id, there is a tendency to think of your school ID card or your driver's license certificate, or such.

But there are lots of user-ids in use on your computer. Whose are they all? Who let them in there? Why?

Maybe we should have used Latin words for the computer jargon, instead of borrowing from living languages. Dead languages are convenient. Or maybe we just could have made up new words. In this case, virtual-user-role-to-manage-a-related-collection-of-tasks, or VURTMARCOT. Shoot, just the acronym is long enough we want to take it out behind the barn and shoot it. I don't want to be talking about a VURTMARCOT-identitfier-number every time I try to figure out what is happening in my system.

So, let's just say that most of the user-ids on your computer are VURTMARCOTs and keep using the term, "user-id", instead.

No?

Uhm, okay, first we have to explain. When your system is running, there are lots of different things going on inside it. Hundreds and thousands of things. The impression that you have that it is complicated is not incorrect. That means that there has to be programs in there to manage the complexity, so that you don't have to. Lots of programs. So many that even the programs to manage the complexity have to be managed.

(Did I really have to say that? I think so.)

So we collected some of those things according to how they are related, and we gave that collection an id number, and we called it a user-id, and we invented  the concept of a (virtual?) system user to manage those things. And we ended up with lots of those system user-ids.

Now, if the system has lots of user-ids for its use, why shouldn't you?

One login user-id for when you are playing around, one for when you are working at your new job, one for the old job, one for when you are going to the bank, one for when you are keeping track of your family records, ...

Well, it's a little inconvenient, because you really don't want to log out and back in every time you shift gears. It's not just a hassle, either, because sometimes what you were playing with turns out to be useful for work, and you want to copy-and-paste from your play area to your work area.

I've blogged about a way to do that. The information is a little old, and I should post an update, with some of the options that I've found to (sort-of) work. But not today.

So, what is a user-id? It's an identifier (both a number and a mnemonic name) that you use to keep track of what's going on in your computer. You may have more than one user-id per human user, and you have lots of user-ids that have no human user.

And you should, in fact, have at least one login user-id for administration tasks, separate from the one you usually log in on to work or whatever.