Linux and Unix file systems are organised in a hierarchical, tree-like structure. The highest level of the file system is the / or root directory. In the Unix and Linux design philosophy, everything is considered a file - including hard disks, partitions and removable media. This means that all other files and directories (including other disks and partitions) exist under the root directory.

For example, /home/jebediah/cheeses.odt shows the correct full path to the cheeses.odt file that exists in the jebediah directory which is under the home directory, which in turn, is under the root (/) directory.

Underneath the root (/) directory, there is a set of important system directories that are common across most Linux distributions that are used. The following is a listing of common directories that are directly under the root (/) directory:

All of the files on a Linux system have permissions that allow or prevent others from viewing, modifying or executing. The super user "root" has the ability to access any file on the system. Each file has access restrictions, user restrictions and have an owner/group association.

Every file is secured by the following three sets of permissions, in order of importance:

Inside each of the three sets of permissions are the actual permissons. The permissions, along with the way they apply differently to files and directories, are outlined below:

To view and edit the permissions on files and directories, open the Applications->Accessories->Home Folder and right-click on a file or directory. Then select Properties. The permissions exist under the Permissions tab and allow for the editing of all permission levels, if you are the owner of the file.

To learn more about file permissions in Linux, read the file permissions page in the Ubuntu Wiki.

Working at the command line is not as daunting a task as you would think. There is no special knowledge needed to know how to use the command line. It is a program like everything else. Most things in Linux can be done using the command line, although there are graphical tools for most programs. Sometimes they are just not enough. This is where the command line comes in handy.

The Terminal is located in Applications->Terminal . The terminal is often called the command prompt or the shell. In days gone by, this was the way the user interacted with the computer. However, Linux users have found that the use of the shell can be quicker than a graphical method and still holds some merit today. Here you will learn how to use the terminal.

The original use of the terminal was a file browser and indeed it is still used as a file browser, in the event of the graphical environment failing. You can use the terminal as a file browser to navigate your files and undo the changes that have been made.

All of the configurations and settings in Linux are saved in text files. Even though you most often can edit configurations through the graphical interface, you may occasionally have to edit them by hand. Mousepad is the default Xubuntu text editor, which you can launch by clicking Applications->Accessories->Mousepad on the desktop menu system.

At times in this guide, Mousepad is run from the command line using gksudo, which runs Mousepad with administrative privileges, in order to modify configuration files.

If you need to use a text editor from the command line, you can use nano, which is a simple to use text editor. When running it from the command line, always use the following command, which ensures that the editor will not introduce line breaks:

nano -w

For more information about how to use nano, refer to the guide on the wiki.

There are also quite a few other terminal-based editors available in Ubuntu. Popular ones include VIM and Emacs (the pros and cons of each are cause for much friendly debate within the Linux community). These are often more complex to use than nano, but are also more powerful.

The root user in GNU/Linux is the user which has administrative access to your system. Normal users do not have this access for security reasons. However, Ubuntu does not enable the root user. Instead, administrative access is given to individual users, who may use the "sudo" application to perform administrative tasks. The first user account you created on your system during installation will, by default, have access to sudo. You can restrict and enable sudo access to users with the Users and Groups application (see the section called “Managing Users and Groups” for more information).

When you run an application that requires root privileges, sudo will ask you to input your normal user password. This ensures that rogue applications cannot damage your system, and serves as a reminder that you are about to perform administrative actions which require you to be careful!

To use sudo when using the command line, simply type "sudo" before the command you wish to run. Sudo will then prompt you for your password.

Sudo will remember your password for 15 minutes (by default). This feature was designed to allow users to perform multiple administrative tasks without being asked for a password each time.

Some other tips for using sudo include:

An incredible amount of information about Linux is available on the Internet. To get started, see the excellent and comprehensive tutorial Getting Started with Linux.

For people who already know the basics, the tutorial Intermediate Level User Linux Course is a good read.