Translations by Seongho Choo

<emphasis role="strong">Note that Linux is case sensitive.</emphasis> User, user, and USER are all different to Linux.

File and Directory Commands

The <command>cd</command> command changes directories. When you open a terminal you will be in your home directory. To move around the file system you will use <command>cd</command>.

To navigate into the root directory, type: <screen>cd /</screen>

To navigate to your home directory, type: <screen>cd</screen> or <screen>cd ~</screen>

The <command>~</command> character represents the current user's home directory. As seen above, <command>cd ~</command> is equivalent to <command>cd /home/username/</command>. However, when running a command as root (using <command>sudo</command>, for example), <command>~</command> points instead to <filename class="directory">/root</filename>. When running a command with <command>sudo</command>, the full path to your home directory must be given.

To navigate up one directory level, type: <screen>cd ..</screen>

To navigate to the previous directory (or back), type: <screen>cd -</screen>

To navigate through multiple levels of directories at once, specify the full directory path that you want to go to. For example, type: <screen>cd /var/www</screen> to go directly to the <filename class="directory">/www</filename> subdirectory of <filename class="directory">/var/</filename>. As another example, type: <screen>cd ~/Desktop</screen> to move you to the <filename class="directory">Desktop</filename> subdirectory inside your home directory.

The <command>pwd</command> command outputs which directory you are currently located in (<acronym>pwd</acronym> stands for <quote>print working directory</quote>). For example, typing <screen>pwd</screen> in the <filename class="directory">Desktop</filename> directory, will show <computeroutput>/home/username/Desktop</computeroutput>. <placeholder-1/>

The <command>ls</command> command outputs a list of the files in the current directory. For example, typing <screen>ls ~</screen> will show you the files that are in your home directory.

Used with the <command>-l</command> options, <command>ls</command> outputs various other information alongside the filename, such as the current permissions on the file, and the file's owner.

The <command>cp</command> command makes a copy of a file. For example, type: <screen>cp foo bar</screen> to make an exact copy of <filename>foo</filename> and name it <filename>bar</filename>. <filename>foo</filename> will be unchanged.

The <command>mv</command> command moves a file to a different location or will rename a file. Examples are as follows: <screen>mv foo bar</screen> will rename the file <filename>foo</filename> to <filename>bar</filename>. <screen>mv foo ~/Desktop</screen> will move the file <filename>foo</filename> to your <filename class="directory">Desktop</filename> directory but will not rename it.

<command>rm</command> is used to delete files. <screen>rm foo</screen> deletes the file <filename>foo</filename> from the current directory.

By default, <command>rm</command> will not remove directories. To remove a directory, you must use the <command>-R</command> option. For example, <screen>rm -R foobar</screen> will remove the directory foobar, <emphasis role="strong">and all of its contents!</emphasis>

The <command>mkdir</command> command allows you to create directories. For example, typing: <screen>mkdir music</screen> will create a directory named <filename class="directory">music</filename> in the current directory.

System Information Commands

The <command>df</command> command displays filesystem disk space usage for all partitions. <screen>df -h</screen> will give information using megabytes (M) and gigabytes (G) instead of blocks (<emphasis role="strong">-h</emphasis> means "human-readable").

The <command>free</command> command displays the amount of free and used memory in the system. <screen>free -m</screen> will give the information using megabytes, which is probably most useful for current computers.

The <command>top</command> command displays information on your GNU/Linux system, running processes and system resources, including CPU, RAM &amp; swap usage and total number of tasks being run. To exit <application>top</application>, press <keycap>q</keycap>.

The <command>uname</command> command with the <emphasis role="strong">-a</emphasis> option, prints all system information, including machine name, kernel name &amp; version, and a few other details. Most useful for checking which kernel you're using.

The following commands will need to be prefaced with the <command>sudo</command> command. Please see <ulink url="https://help.ubuntu.com/community/RootSudo">RootSudo</ulink> for information on using <command>sudo</command>.

The <command>addgroup</command> command is used to create a new group on the system. To create a new group, type: <screen>addgroup newgroup</screen> The above command will create a new group called <emphasis role="strong">newgroup</emphasis>.

The <command>adduser</command> is used to create new users on the system. To create a new user, type: <screen>adduser newuser</screen> The above command will create a new user called <emphasis role="strong">newuser</emphasis>.

The default behavior for a command may usually be modified by adding a <emphasis role="strong">-- <emphasis>option</emphasis></emphasis> to the command. The <link linkend="ls"><command>ls</command></link> command, for example, has a <emphasis role="strong">-s</emphasis> option so that <command>ls -s</command> will include file sizes in the listing. There is also a <emphasis role="strong">-h</emphasis> option to get those sizes in a "human readable" format.

Virtually all commands understand the <emphasis role="strong">-h</emphasis> (or <emphasis role="strong">--help</emphasis>) option which will produce a short usage description of the command and it's options, then exit back to the command prompt. Type <screen>man -h</screen> or <screen>man --help</screen> to see this in action.

Every command and nearly every application in Linux will have a man (manual) file, so finding them is as simple as typing <command>man command</command> to bring up a longer manual entry for the specified command. For example, <screen>man mv</screen> will bring up the <command>mv</command> (move) manual.

Move up and down the man file with the arrow keys, and quit back to the command prompt with <keycap>q</keycap>.

<screen>man man</screen> will bring up the manual entry for the <command>man</command> command, which is a good place to start.

<screen>man intro</screen> is especially useful - it displays the "Introduction to user commands" which is a well-written, fairly brief introduction to the Linux command line.

If you aren't sure which command or application you need to use, you can try searching the man files.

This is the same as the <command>apropos</command> command.

This is the same as the <command>whatis</command> command.

Cutting and pasting

Often, you will be referred to instructions that require commands to be pasted into the terminal.

You might be wondering why the text you've copied from a web page using <keycombo><keycap>Ctrl</keycap><keycap>C</keycap></keycombo> won't paste in with <keycombo><keycap>Ctrl</keycap><keycap>V</keycap></keycombo>, the shell uses a different combination for paste <keycombo><keycap>Shift</keycap><keycap>Insert</keycap></keycombo>. This can also be done using the mouse, by right-clicking in the terminal and clicking <menuchoice><guimenuitem>Paste</guimenuitem></menuchoice> from the menu.

You can also select the required commands in your web browser and then subsequently click the middle button on your mouse (or simply click buttons simultaneously on a two-button mouse) in the terminal to paste in the select command.

These actions may mean something entirely different to other terminal emulators. Consult your emulator's documentation for details.

Scrolls through the commands you've entered previously.

Takes you back to a more recent command.

When you have the command you want.

A very useful feature. It autocompletes any commands or filenames, if there's only one option, or else gives you a list of options.