Permissions and Users
Mac Tip #109/09-July-2003

This Tip applies only to Mac OS X. If you don’t have OS X read it anyway — one day you might find it useful.

Mac OS X works on the assumption that more than one person will use the computer. According to this model each user can have a certain level of access and authority.

There are three types of user.

Admin users have a lot of power

If you are the only person using your Mac then you probably have admin access. You’re allowed to install software and just get on with regular, normal things.

If you have a visitor come to stay then you might set up a new user, let’s call her “Alice”. This is easy to do but I’ll cover it in another tip.

Guest users have less power

Let’s say you want Alice to be able to surf the web and play a few games but not install or remove anything. You can set her up as a guest user and restrict her permissions so she can do only those things you’ve allowed her to do. And what’s more she can’t get into your files.

The ‘super’ user can do anything

Now, as the Admin user you can do any number of things on your computer, but there are some things even you can’t do.

On rare occasions you might need to log in as a third kind of user. This user is very special and exists on every Mac automatically. This super-user is known as Root and can do anything at all on the Mac.

The Root user can delete crucial files, tinker with anyone’s files, generally wreak havoc on the machine. For that reason it’s not easy to log in as the Root user — you won’t accidentally find yourself with this capability.

All these different levels of permission mean that your Mac has to keep track of who is allowed to do what with each file. This works by having a set of information attached to each file specifying who can read, write and execute it.

This may not mean much to you today, but in the next tip we’ll build on it to help you keep your Mac running smoothly.