Becoming SuperUser
No phone booth needed. The obvious way is to login as root. That's the best way to do it if you plan on doing a bunch of system maintenance type stuff, but it can be a pain if you're logged in as User with an X session and 14 programs open and connected to the Internet and you just need to copy one file into /usr/lib so you can run this program you just downloaded. Fear not, there is a better way. Type this:
[user]$ su
Password:*****
[root]#
Bang! Just like that, you are SuperUser! A few cautions: Although you are now SuperUser, this is not a "login" shell, so your environment hasn't changed. The biggest way this will effect you is that some programs you normally run as root may appear to be missing. That's because your PATH environment variable, the list of places Linux looks for executables, does not contain /sbin or /usr/sbin. If you try to run a command like shutdown (see below) and it complains, try typing /sbin/shutdown instead. That should do it.
When you are finished with your maintenance tasks you should immediately change back to normal user mode:
[root]# exit
[user]$
Notice that while you are SuperUser, your command prompt looks different. An ordinary user is prompted with the dollar sign ($) while SuperUser gets a pound sign (#). This makes it easy to tell which mode you are in. (This is true on most distributions, but the prompts may be different on different distributions, and they can be customized.)