To reboot, just type reboot or press Ctrl-Alt-Del (that’s Ctrl, Alt, and Delete).
To shut down, you’ll have to log in as root. As root, just type the command shutdown -h now. The sytem will go through the entire shutdown procedure, including the sync command, which clears the disk cache as described above. When you see System halted, it’s safe to turn off the computer. If you have Advanced Power Management (APM) support in your kernel and BIOS, the computer might shut itself off and save you the trouble. APM is common in laptops and is also found in certain desktop mainboards.
It’s now time to explore the system in more detail. You’ve seen how to log in and shut down the system. In this chapter, we explore the Linux comand line, how Linux deals with files and directories, and some basics on identifying yourself to others.
We’ve already discussed the command line—that is, commands you type after the shell prompt. This section describes the structure of more complicated command lines.
A minimal command line contains just a command name, such as whoami. But other things are possible. For example, you might type: man whoami. This command requests the online manual for the whoami program (you may have to press the space bar to scroll through the documentation or press q to quit). A more complicated example is man -k PostScript. This command line has three parts. It begins with the command name, man. Then it has an _option_ or _switch_, -k, followed by an _argument_, PostScript. Some people refer to everything except the command name as the _parameters_ of the command. So, options and arguments are both parameters.
Options change the behavior of a command, switching on particular features or functionality. They usually have a - before them. The GNU utilities also have “long forms” for the options; the long form of -k is -apropos. You can enter man -h or man -help to get a full list of options for the man command. Every command will have its own set of options, though most have -help and -version options. Some commands, such as tar, do not require the “-” before their options for historical reasons.
Anything that isn’t an option and isn’t the command name is an _argument_ (in this case, PostScript). Arguments can serve many purposes; most commonly, they are filenames that the command should operate on. In this case, PostScript is the word you want man to search for. In the case of man whoami, the argument was the command you wanted information about.