2.2. Absolute basics

2.2.1. The commands

These are the quickies, which we need to get started; we will discuss them later in more detail.

Table 2-1. Quickstart commands


Displays a list of files in the current working directory, like the dir command in DOS

cd directory

change directories

passwdchange the password for the current user
file filenamedisplay file type of file with name filename
cat textfilethrows content of textfile on the screen
pwddisplay present working directory
exit or logoutleave this session
man commandread man pages on command
info commandread Info pages on command
apropos stringsearch the whatis database for strings

2.2.2. General remarks

You type these commands after the prompt, in a terminal window in graphical mode or in text mode, followed by Enter.

Commands can be issued by themselves, such as ls. A command behaves different when you specify an option, usually preceded with a dash (-), as in ls -a. The same option character may have a different meaning for another command. GNU programs take long options, preceded by two dashes (--), like ls --all. Some commands have no options.

The argument(s) to a command are specifications for the object(s) on which you want the command to take effect. An example is ls /etc, where the directory /etc is the argument to the ls command. This indicates that you want to see the content of that directory, instead of the default, which would be the content of the current directory, obtained by just typing ls followed by Enter. Some commands require arguments, sometimes arguments are optional.

You can find out whether a command takes options and arguments, and which ones are valid, by checking the online help for that command, see Section 2.3.

In Linux, like in UNIX, directories are separated using forward slashes, like the ones used in web addresses (URLs). We will discuss directory structure in-depth later.

The symbols . and .. have special meaning when directories are concerned. We will try to find out about those during the exercises, and more in the next chapter.

Try to avoid logging in with or using the system administrator's account, root. Besides doing your normal work, most tasks, including checking the system, collecting information etc., can be executed using a normal user account with no special permissions at all. If needed, for instance when creating a new user or installing new software, the preferred way of obtaining root access is by switching user IDs, see Section 3.2.1 for an example.

Almost all commands in this book can be executed without system administrator privileges. In most cases, when issuing a command or starting a program as a non-privileged user, the system will warn you or prompt you for the root password when root access is required. Once you're done, leave the application or session that gives you root privileges immediately.

Reading documentation should become your second nature. Especially in the beginning, it is important to read system documentation, manuals for basic commands, HOWTOs and so on. Since the amount of documentation is so enormous, it is impossible to include all related documentation. This book will try to guide you to the most appropriate documentation on every subject discussed, in order to stimulate the habit of reading the man pages.

2.2.3. Using Bash features

Several special key combinations allow you to do things easier and faster with the GNU shell, Bash, which is the default on almost any Linux system, see Section Below is a list of the most commonly used features; you are strongly suggested to make a habit out of using them, so as to get the most out of your Linux experience from the very beginning.

Table 2-2. Key combinations in Bash

Key or key combinationFunction
Ctrl+AMove cursor to the beginning of the command line.
Ctrl+CEnd a running program and return the prompt, see Chapter 4.
Ctrl+DLog out of the current shell session, equal to typing exit or logout.
Ctrl+EMove cursor to the end of the command line.
Ctrl+HGenerate backspace character.
Ctrl+LClear this terminal.
Ctrl+RSearch command history, see Section
Ctrl+ZSuspend a program, see Chapter 4.
ArrowLeft and ArrowRightMove the cursor one place to the left or right on the command line, so that you can insert characters at other places than just at the beginning and the end.
ArrowUp and ArrowDownBrowse history. Go to the line that you want to repeat, edit details if necessary, and press Enter to save time.
Shift+PageUp and Shift+PageDownBrowse terminal buffer (to see text that has "scrolled off" the screen).
TabCommand or filename completion; when multiple choices are possible, the system will either signal with an audio or visual bell, or, if too many choices are possible, ask you if you want to see them all.
Tab TabShows file or command completion possibilities.

The last two items in the above table may need some extra explanations. For instance, if you want to change into the directory directory_with_a_very_long_name, you are not going to type that very long name, no. You just type on the command line cd dir, then you press Tab and the shell completes the name for you, if no other files are starting with the same three characters. Of course, if there are no other items starting with "d", then you might just as wel type cd d and then Tab. If more than one file starts with the same characters, the shell will signal this to you, upon which you can hit Tab twice with short interval, and the shell presents the choices you have:

your_prompt> cd st
starthere	 stuff		stuffit

In the above example, if you type "a" after the first two characters and hit Tab again, no other possibilities are left, and the shell completes the directory name, without you having to type the string "rthere":

your_prompt> cd starthere

Of course, you'll still have to hit Enter to accept this choice.

In the same example, if you type "u", and then hit Tab, the shell will add the "ff" for you, but then it protests again, because multiple choices are possible. If you type Tab Tab again, you'll see the choices; if you type one or more characters that make the choice unambiguous to the system, and Tab again, or Enter when you've reach the end of the file name that you want to choose, the shell completes the file name and changes you into that directory - if indeed it is a directory name.

This works for all file names that are arguments to commands.

The same goes for command name completion. Typing ls and then hitting the Tab key twice, lists all the commands in your PATH (see Section 3.2.1) that start with these two characters:

your_prompt> ls
ls           lsdev        lspci        lsraid       lsw
lsattr       lsmod        lspgpot      lss16toppm
lsb_release  lsof         lspnp        lsusb