Changing Directories with cd

Changing directories is easy as long as you know where you are (your current directory) and how that relates to where you want to go.

To change directories, use the cd command. This command by itself will always return you to your home directory; moving to any other directory requires a pathname.

You can use absolute or relative pathnames. Absolute paths start at the top with / (referred to as root) and then look down for the requested directory; relative paths look down from your current directory, wherever that may be. The tree below is used only as an example for the purpose of explaining cd.

/
directory1
directory2
directory3

If you are currently in directory3 and you want to switch to directory1, you need to move up in the directory tree.

Executing the command

cd directory1 

while you are in directory3, will present you with an error message explaining that there is no such directory. This is because there is no directory1 below directory3.

To move up to directory1, type:

cd /directory1 

This is an example of an absolute path. It tells Linux to start at the top (/) and look down until it finds directory1. A path is absolute if the first character is a /. Otherwise, it is a relative path.

Absolute paths will take you to any directory, from any directory. Relative paths will only take you to directories below your current one.

Use the following exercise to test what you have learned so far regarding absolute and relative paths. From your home directory, type the relative path:

cd ../../etc/X11

The command cd .. tells your system to go up to the directory immediately above the one in which you are currently working. cd ../.. tells it to go up two directories.

After using the full command in the example, you should be in the directory /X11, which is where you will find configuration files and directories related to the X Window System.

Take a look at your last cd command. You told your system to:

1. Go up one level to your login directory's parent directory (probably /home)

2. Then go up to that directory's parent (which is the root, or /, directory)

3. Then go down to the etc directory

4. Finally, go to the X11 directory

Conversely, using an absolute path would get you to the /etc/X11 directory more quickly. For example:

cd /etc/X11

	Note
	Always make sure you know which working directory you are in before you state the relative path to the directory or file you want to get to. You do not have to worry about your position in the file system, though, when you state the absolute path to another directory or file. If you are not sure, type pwd.

Now that you are starting to understand how to change directories, see what happens when you change to root's login directory (the superuser account). Type:

cd /root

If you are not logged in as root, you are denied permission to access that directory.

Denying access to the root and other users' accounts (or login directories) is one way your Linux system prevents accidental or malicious tampering. See the Section called Ownership and Permissions.

To change to the root login and root directory, use the su command. For example:

[sam@halloween sam]$su
Password:your root password
[root@halloween sam]#cd /root
[root@halloween /root]#

	Tip
	The command su means substitute users and it allows you to temporarily log in as another user. When you type su all by itself and press [Enter], you become root (also called the superuser) while still inside your login shell (your user's home directory). Typing su - makes you become root with root's login shell — that is, it is as if you had logged in as root originally.

As soon as you give the root password, you will see the changes in your command prompt to show your new, superuser status, the root account designation at the front of the prompt and "#" at the end (as shown in the prior example).

When you are done working as root, type exit at the prompt and you will return to your user account.

[root@halloween /root]#exit
exit
[sam@halloween sam]$