Linux Server Configuration

1.3 Files And Directories

A directory is a collection of files and/or other directories. Because a directory can contain other directories, we get a directory hierarchy. The top level of the hierarchy is the root directory. Files and directories can be named by a path. The root directory is referred to as /. Other directories are referred to by the path. The path consists of names separated by /. A file can also be referred to by the path. If it is directory, then the path may end with a /.

An absolute path starts at the root of the directory hierarchy and names directories or files under it. For example:

/etc/hostname

The above refers to a file hostname which is in the etc directory under the root (/) directory.

1.3.1 List The Names of Files In A Director: ls

We can use ls command to list files in a specific directory by specifying the specific directory:

$ ls /usr/share/doc/

The above command lists all he files and folders under the directory /usr/share/doc. If the first argument to ls is not given, then ls lists the files in current working directory of he user.

The -l option to ls gives more information, including the size of files and the date they were last modified:

$ ls -l

drwxrwxr-x 2 fred users 4096 Jan 21 10:57 Accounts
-rw-rw-r-- 1 fred users 345 Jan 21 10:57 notes.txt
-rw-r--r-- 1 fred users 3255 Jan 21 10:57 report.txt

1.3.2 Viewing And Changing Current Directory: pwd, cd

The shell has a current directory – the directory in which currently the logged user is working in shell. Usually after firs login, the current directory should be the home directory of the user. Some commands like ls use the current directory if none is specified. We use pwd command to see what the current directory is:

$ pwd

/home/fred

We can change the current directory with the command cd :

$ cd /mnt/cdrom
$ pwd
/mnt/cdrom

The symbol tlide (~) is an abbreviation for home directory. So for user fred the following are equivalent:

$ cd /home/fred/documents/

$ cd ˜/documents/

The following are the same for user fred:

$ cd

$ cd ˜
$ cd /home/fred

Paths do not have to start from the root directory. A path which does not start with the / is a relative path. It is relative to some other directory usually current directory. Relative paths specify files in the same way as the absolute ones. For example the following sets of directory changes end up in the same directory

$ cd /usr/share/doc

$ cd /

$ cd usr
$ cd share/doc

Every directory contains two special filenames which help making relative paths.

The directory .. points to the parent directory. ls .. will list files in the parent directory

For example if we start from /home/fred:

$ cd ..

$ pwd
/home
$ cd ..
$ pwd
/

The directory . points to the directory it is in. sp ./foo is the same file as foo.

The special .. and . directories can be used in paths just like any other directory names:

$ cd ../other-dir/

The above means the directory other-dir in the parent directory of the current directory. It is common to see .. to go back several directories from the current directory. The dot directory is most commonly used on its own to mean the current directory.