In this chapter, you will climb a very special tree, which is the Linux filesystem. During this climbing journey, you will learn:

• The Linux filesystem hierarchy.
• What is the root directory?
• Absolute versus Relative paths.
• How to navigate the Linux filesystem.

Alright, you are at the root of the tree and ready to climb up. In Linux, just like an actual tree, the beginning of the filesystem starts at the root directory. You can use the cd command followed by a forward slash to get to the root:

elliot@ubuntu-linux:~$ cd /

The cd command is short for Change Directory and is one of the most used commands in Linux. You can't move around in Linux without it. It's like your limbs (arms and legs), can you climb a tree without your limbs?
The forward slash character represents the root directory. Now to make sure you're at the root directory, you can run pwd:

elliot@ubuntu-linux:~$ pwd
/

And sure enough, we are at the root of the Linux filesystem. Whenever you are lost and you don't know where you are, pwd is here to rescue you.

Alright, while we are still at the root directory, let's see what's in there! Run the ls command to view the contents of the current directory:

elliot@ubuntu-linux:/$ ls
bin etc lib proc tmp var boot 
dev home opt root sbin usr

To have a better view of the contents, you can use the long listing -l option with the ls command:

elliot@ubuntu-linux:/$ ls -l
drwxr-xr-x   2 root root           4096 Dec 28 15:36 bin
drwxr-xr-x 125 root root          12288 Jan  1 11:01 etc
drwxr-xr-x  21 root root           4096 Dec 26 23:52 lib
dr-xr-xr-x 227 root root              0 Jan  3 02:33 proc
drwxrwxrwt  15 root root           4096 Jan  3 02:35 tmp
drwxr-xr-x  14 root root           4096 Jul 24 21:14 var
drwxr-xr-x   3 root root           4096 Dec 29 07:17 boot
drwxr-xr-x  18 root root           4000 Jan  3 02:33 dev
drwxr-xr-x   3 root root           4096 Dec 26 23:47 home
drwxr-xr-x   3 root root           4096 Dec 27 15:07 opt
drwx------   4 root root           4096 Dec 29 09:39 root
drwxr-xr-x   2 root root          12288 Dec 28 15:36 sbin
drwxr-xr-x  10 root root           4096 Jul 24 21:03 usr

This output gives you a lot of valuable information that we will discuss in detail in the upcoming chapters. But for now, we focus on the first letter in the first column of the output. Take a look at the first column of the output:

drwxr-xr-x 
drwxr-xr-x 
drwxr-xr-x 
drwxr-xr-x
.
.
.
.

You will see that the first letter is d, which means that the file is a directory. The first letter reveals the file type. The last column of the output displays the filename.

Now each one of these directories has a special purpose, as you can see in the following table:

You can also run the man hier command to read more about the Linux filesystem hierarchy:

elliot@ubuntu-linux:/$ man hier

Alright, now let's do further climbing on the Linux directory tree. Take a look at figure 1, and you will understand why we choose a tree to describe the structure of the Linux filesystem.

The preceding figure only features very few files and by no means is a representation for the whole directory tree, as the Linux filesystem literally contains thousands of files. So you can think of the preceding figure as a subtree of the actual Linux directory tree.

Alright, let's do more climbing. For example, let's climb to the /home directory to see how many users we have on the system. You can do that by simply running the cd /home command:

elliot@ubuntu-linux:~$ cd /home 
elliot@ubuntu-linux:/home$

Notice how your command prompt changes as it's now showing that you are at the home directory.

Now let's run ls to view the contents of the /home directory:

elliot@ubuntu-linux:/home$ ls 
angela elliot

These are the two users on my system (besides the root user). The /root is the home directory for the root user. You probably have only one user in /home; you will learn later in the book how to add other users to your system.

If you want proof that you are currently at the /home directory, you can run the pwd command:

elliot@ubuntu-linux:/home$ pwd
/home

Sure enough! We are at the /home directory. Now let's climb to the home directory of user elliot. Now, believe it or not, there are two ways to navigate to elliot's home directory. You can simply run the cd elliot command:

elliot@ubuntu-linux:/home$ cd elliot 
elliot@ubuntu-linux:~$ pwd
/home/elliot

Or you can run the cd /home/elliot command:

elliot@ubuntu-linux:/home$ cd /home/elliot 
elliot@ubuntu-linux:~$ pwd
/home/elliot

Notice that both commands have landed us in elliot's home directory. However, running cd elliot is much easier than running cd /home/elliot, of course.

Well, think about it, we were initially at the /home directory, and that's why we were able to run cd elliot to land in /home/elliot.

However, in other situations, we would be forced to use the full path (absolute path) /home/elliot to reach our destination. To demonstrate, let's first change to the /etc directory:

elliot@ubuntu-linux:~$ cd /etc 
elliot@ubuntu-linux:/etc$ pwd
/etc

Figures 4 and 5 help you visualize it. You are at /etc and you want to go to /home/elliot. To get to elliot's home directory, we can no longer use a short path (relative path) by running the cd elliot command:

elliot@ubuntu-linux:/etc$ cd elliot
bash: cd: elliot: No such file or directory

As you can see, the Shell got mad and returned an error bash: cd: elliot: No such file or directory. In this case, we have to use the full path (absolute path)/home/elliot:

elliot@ubuntu-linux:/etc$ cd /home/elliot 
elliot@ubuntu-linux:~$ pwd
/home/elliot

In case you haven't noticed by now, we have been using the forward slash (/) as a directory separator.

It's crucial to realize the difference between absolute paths and relative paths.

As a rule of thumb, if you want to distinguish between a relative path and an absolute path, look and see if the path starts with the root directory (forward slash); if it does, then you can conclude the path is absolute, otherwise, the path is relative.

The following diagram shows you the relative path Desktop/hello.txt and will only work if your current working directory is /home/elliot.

The following image shows you the absolute path /home/elliot/Desktop and will always work regardless of your current working directory.

Now let's climb to Elliot's Desktop directory to see what he has there. We will use an absolute path:

elliot@ubuntu-linux:/$ cd /home/elliot/Desktop 
elliot@ubuntu-linux:~/Desktop$ pwd
/home/elliot/Desktop

We follow it with a pwd to confirm that we are indeed in the desired directory. Now let's run ls to view the contents of Elliot's desktop:

elliot@ubuntu-linux:~/Desktop$ ls 
hello.txt

Notice that the file hello.txt is on Elliot's desktop, so we can actually see it right there on the desktop.

As you can see in the preceding image, there is a file named hello.txt on Elliot's desktop. You can use the cat command to view the contents of a text file:

elliot@ubuntu-linux:~/Desktop$ cat hello.txt 
Hello Friend!
Are you from fsociety?

If you open the file hello.txt on the desktop, you will see the same contents, of course, as you can see in the following screenshot.

There are two special directories under every directory in the filesystem:

1. Current working directory represented by one dot (.)
2. Parent directory represented by two dots (..)

It's easy to understand both directories by going through a few examples. To demonstrate, let's first change to /home/elliot so that it becomes our current working directory:

elliot@ubuntu-linux:~/Desktop$ cd /home/elliot 
elliot@ubuntu-linux:~$ pwd
/home/elliot

Now run the cd . command:

elliot@ubuntu-linux:~$ cd . 
elliot@ubuntu-linux:~$ pwd
/home/elliot

As you would expect, nothing happened! We are still at /home/elliot, and that is because one dot (.) represents the current working directory. It's like if you told someone, "Go where you are!"

Now run the cd .. command:

elliot@ubuntu-linux:~$ cd .. 
elliot@ubuntu-linux:/home$ pwd
/home

We moved back one directory! In other words, we changed to the parent directory of /home/elliot, which is /home.

Let's run another cd ..:

elliot@ubuntu-linux:/home$ cd .. 
elliot@ubuntu-linux:/$ pwd
/

Indeed we keep going back, and now we are at the root of our directory tree. Well, let's run cd .. one more time:

elliot@ubuntu-linux:/$ cd .. 
elliot@ubuntu-linux:/$ pwd
/

Hmmm, we are at the same directory! Our path didn't change, and that's because we are at the root of our directory tree already, so we can't go any further back. As a result, the root directory (/) is the only directory where the parent directory = current directory, and you can visualize it by looking at figure 10.

You can also insert the directory separator cd ../.. to move back two directories at once:

elliot@ubuntu-linux:~$ pwd
/home/elliot
elliot@ubuntu-linux:~$ cd ../.. 
elliot@ubuntu-linux:/$ pwd
/

You can also run cd ../../.. to move back three directories and so on.

Now I will show you some cool tricks that will make you fast and efficient in navigating the Linux directory tree.

Go back home!

Let's change to the /var/log directory:

elliot@ubuntu-linux:~$ cd /var/log 
elliot@ubuntu-linux:/var/log$ pwd
/var/log

You can now run the cd ~ command to go to your home directory:

elliot@ubuntu-linux:/var/log$ cd ~ 
elliot@ubuntu-linux:~$ pwd
/home/elliot

WOW! Let's do it again, but this time, we switch to user angela. In case you don't know, the character is called tilde and should be located next to your number 1 key on your keyboard:

elliot@ubuntu-linux:~$ whoami 
elliot
elliot@ubuntu-linux:~$ su angela 
Password:
angela@ubuntu-linux:/home/elliot$ whoami 
angela

Notice here I used two new commands. The whoami command prints the name of the currently logged-in user. I also used the switch user su command to switch to user angela. You can use the su command to switch to any user on your system; you just need to run su, followed by the username.

Now, as user angela, I will navigate to the /var/log directory:

angela@ubuntu-linux:/home/elliot$ cd /var/log 
angela@ubuntu-linux:/var/log$ pwd
/var/log

Then I run the cd ~ command:

angela@ubuntu-linux:/var/log$ cd ~ 
angela@ubuntu-linux:~$ pwd
/home/angela

Boom! I am at Angela's home directory. Regardless of your current working directory, running the cd ~ command will land you straight to your home directory.

Take me back!

Now, what if angela wants to go back as quickly as possible to her previous working directory?

Running the cd - command is the fastest method that will land angela back to her previous working directory:

angela@ubuntu-linux:~$ pwd
/home/angela
angela@ubuntu-linux:~$ cd -
/var/log

Cool! angela is back in /var/log. So anytime you want to go back to your previous working directory, just run the cd - command.

The current directory . and the parent directory .. exist under each directory in the Linux filesystem. But how come we can't see them when we run the ls command?

elliot@ubuntu-linux:~/Desktop$ pwd
/home/elliot/Desktop 
elliot@ubuntu-linux:~/Desktop$ ls 
hello.txt
elliot@ubuntu-linux:~/Desktop$ ls -l 
total 4
-rw-r--r-- 1 elliot elliot 37 Jan 19 14:20 hello.txt

As you can see, I even tried to run ls -l and still can't see the current directory or the parent directory.

You need to use the -a option with the ls command as follows:

elliot@ubuntu-linux:~/Desktop$ ls -a
. .. hello.txt

Hooray! Now you can see all the files. The -a option shows you all the files, including hidden files and of course you can use the full option name --all, which will do the same thing:

elliot@ubuntu-linux:~/Desktop$ ls --all
. .. hello.txt

It turns out that any filename that starts with . (a dot) is hidden.

To demonstrate further, go to your user home directory and run the ls command:

angela@ubuntu-linux:~$ ls 
Music

Now run the ls -a command:

angela@ubuntu-linux:~$ ls -a
. .. .bash_logout .bashrc Music .profile

You can now see the hidden files in your home directory! Notice all the hidden filenames start with a dot.

So far, we ran the ls command only on the current working directory. However, you can list the contents of any directory without having to change to it. For example, if your current working directory is /home/elliot:

elliot@ubuntu-linux:~$ pwd
/home/elliot

You can list all the files in /home/angela by running the ls -a /home/angela command:

elliot@ubuntu-linux:~$ ls -a /home/angela
. .. .bash_history .bash_logout .bashrc Music .profile 
elliot@ubuntu-linux:~$ pwd
/home/elliot 
elliot@ubuntu

I was able to list the contents of /home/angela while still being in /home/elliot. This is possible because the ls command accepts any file as an argument.

You can see in the preceding image the general structure of a Linux command.

In Linux terminology, we use the verb pass when talking about command options and arguments. To use the correct Linux terminology, for example, in the preceding image, we say, "We passed the /home/angela directory as an argument to the ls command."

You will often find Linux users very keen on using the right terminology. Moreover, using the proper terminology can help you pass a job interview and land your dream job!

Notice in the preceding figure, we used the plural nouns options and arguments. That's because some commands can accept multiple options and arguments.

For example, we can do a long listing for all the files in /home/angela by running the ls -a -l /home/angela command:

elliot@ubuntu-linux:~$ ls -a -l /home/angela 
total 28
drwxr-xr-x 3 angela angela 4096 Jan 20 13:43 .
drwxr-xr-x 9  root    root 4096 Jan 17 04:37 ..
-rw------- 1 angela angela   90 Jan 20 13:43 .bash_history
-rw-r--r-- 1 angela angela  220 Apr  4  2018 .bash_logout
-rw-r--r-- 1 angela angela 3771 Apr  4  2018 .bashrc
drwxrwxr-x 2 angela angela 4096 Jan 19 19:42 Music
-rw-r--r-- 1 angela angela  807 Apr  4  2018 .profile

So now you see a long listing of all the files in /home/angela including the hidden files, also notice that the ordering of the options doesn't matter here, so if you run the ls -l -a /home/angela command:

elliot@ubuntu-linux:~$ ls -l -a /home/angela 
total 28
drwxr-xr-x 3 angela angela 4096 Jan 20 13:43 .
drwxr-xr-x 9   root   root 4096 Jan 17 04:37 ..
-rw------- 1 angela angela   90 Jan 20 13:43 .bash_history
-rw-r--r-- 1 angela angela  220 Apr  4  2018 .bash_logout
-rw-r--r-- 1 angela angela 3771 Apr  4  2018 .bashrc
drwxrwxr-x 2 angela angela 4096 Jan 19 19:42 Music
-rw-r--r-- 1 angela angela  807 Apr  4  2018 .profile

You will get the same result. This was an example of passing two commands options, what about passing two arguments? Well, you can do a long listing for all the files in /home/angela and /home/elliot at the same time by passing /home/elliot as a second argument:

elliot@ubuntu-linux:~$ ls -l -a /home/angela /home/elliot
/home/angela:
 
total 28
drwxr-xr-x 3 angela angela 4096 Jan 20 13:43 .
drwxr-xr-x 9 root   root   4096 Jan 17 04:37 ..
-rw------- 1 angela angela   90 Jan 20 13:43 .bash_history
-rw-r--r-- 1 angela angela  220 Apr  4  2018 .bash_logout
-rw-r--r-- 1 angela angela 3771 Apr  4  2018 .bashrc
drwxrwxr-x 2 angela angela 4096 Jan 19 19:42  Music
-rw-r--r-- 1 angela angela  807 Apr  4  2018 .profile

/home/elliot:
total 28
drwxr-xr-x 3 elliot elliot 4096 Jan 20 16:26 .
drwxr-xr-x 9 root   root   4096 Jan 17 04:37 ..
-rw------- 1 elliot elliot   90 Jan 20 13:43 .bash_history
-rw-r--r-- 1 elliot elliot  220 Dec 26 23:47 .bash_logout
-rw-r--r-- 1 elliot elliot 3771 Dec 26 23:47 .bashrc
drwxr-xr-x 2 elliot elliot 4096 Jan 19 14:20  Desktop
-rw-r--r-- 1 elliot elliot  807 Apr 4   2018 .profile

So now, you can see the contents of both the /home/elliot and /home/angela directories at the same time.

Let's do a long listing for all the files in /home/elliot one more time to discuss something very important:

elliot@ubuntu-linux:~$ ls -a -l /home/elliot 
total 28
drwxr-xr-x 3 elliot elliot 4096 Jan 20 16:26 .
drwxr-xr-x 9 root   root   4096 Jan 17 04:37 ..
-rw------- 1 elliot elliot   90 Jan 20 13:43 .bash_history
-rw-r--r-- 1 elliot elliot  220 Dec 26 23:47 .bash_logout
-rw-r--r-- 1 elliot elliot 3771 Dec 26 23:47 .bashrc
drwxr-xr-x 2 elliot elliot 4096 Jan 19 14:20  Desktop
-rw-r--r-- 1 elliot elliot  807 Apr  4  2018 .profile

Focus on the last two columns of the output:

You already know that the last column of the output (2nd column of Table 3) shows the filenames, but what about all these dates that are displayed in the preceding column (1st column of Table 3)?

The dates in the first column of Table 3 represent the last modification time of each file, which is the last time a file was modified (edited).

You can use the touch command to change the modification time of a file.

To demonstrate, let's first get the modification time on elliot's Desktop directory, you can do that by running the ls -l -d /home/elliot/Desktop command:

elliot@ubuntu-linux:~$ ls -l -d /home/elliot/Desktop
drwxr-xr-x 2 elliot elliot 4096 Jan 19 14:20 /home/elliot/Desktop

Notice we used the -d option, so it does a long listing on the directory /home/elliot/Desktop instead of listing the contents of the directory.

The last modification time is shown to be: Jan 19 14:20.

Now if you run the touch /home/elliot/Desktop command:

elliot@ubuntu-linux:~$ touch /home/elliot/Desktop 
elliot@ubuntu-linux:~$ ls -l -d /home/elliot/Desktop
drwxr-xr-x 2 elliot elliot 4096 Jan 20 19:42 /home/elliot/Desktop 
elliot@ubuntu-linux:~$ date
Sun Jan 20 19:42:08 CST 2020

You will see that the last modification time of the directory /home/elliot/Desktop has now changed to Jan 20 19:42, which reflects the current time.

Of course, you will get a different result on your system because you will not be running the command at the same time as me.

Ok, great, so now we understand that the touch command can be used to update a file's modification time. Can it do something else? Hmmm, let's see.

What if we try to update the modification time of a file that doesn't exist? What will happen? The only way to know is to try it. Notice that user elliot has only one visible (not hidden) file in his home directory, which happens to be the Desktop directory:

elliot@ubuntu-linux:~$ pwd
/home/elliot
elliot@ubuntu-linux:~$ ls -l 
total 4
drwxr-xr-x 2 elliot elliot 4096 Jan 20 19:42 Desktop

Now watch what will happen when user elliot runs the touch blabla command:

elliot@ubuntu-linux:~$ touch blabla 
elliot@ubuntu-linux:~$ ls -l
total 4
-rw-r--r-- 1 elliot elliot    0 Jan 20 20:00 blabla
drwxr-xr-x 2 elliot elliot 4096 Jan 20 19:42 Desktop

It created an empty file named blabla.

You can do two things with the touch command:

1. You can update the last modification and access times of existing files.
2. You can create new empty files.

The touch command can only create regular files; it cannot create directories. Also, notice that it updates modification and access times, so what is the difference?

• Modification Time > Last time a file was changed or modified.
• Access Time > Last time a file was accessed (read).

By default, the touch command changes both the modification and access times of a file. I have created three files in elliot's home directory: file1, file2, and file3:

elliot@ubuntu-linux:~$ ls -l 
total 8
drwxr-xr-x 6 elliot elliot 4096 Jan 25 22:13 Desktop
drwxr-xr-x 3 elliot elliot 4096 Jan 25 22:18 dir1
-rw-r--r-- 1 elliot elliot    0 Feb 29  2004 file1
-rw-r--r-- 1 elliot elliot    0 Apr 11  2010 file2
-rw-r--r-- 1 elliot elliot    0 Oct  3  1998 file3

Now to change only the modification time of file1. We pass the -m option to the touch command:

elliot@ubuntu-linux:~$ touch -m file1 
elliot@ubuntu-linux:~$ ls -l
total 8
drwxr-xr-x 6 elliot elliot 4096 Jan 25 22:13 Desktop
drwxr-xr-x 3 elliot elliot 4096 Jan 25 22:18 dir1
-rw-r--r-- 1 elliot elliot    0 Jan 25 23:08 file1
-rw-r--r-- 1 elliot elliot    0 Apr 11  2010 file2
-rw-r--r-- 1 elliot elliot    0 Oct  3  1998 file3 
elliot@ubuntu-linux:~$

As you can see, the modification time of file1 has now changed. I promised you I would only change the modification time, right? If you pass the -u option along with the -l option to the ls command, you will get the last access times instead of the modification times:

elliot@ubuntu-linux:~$ ls -l 
total 8
drwxr-xr-x 6 elliot elliot 4096 Jan 25 22:13 Desktop
drwxr-xr-x 3 elliot elliot 4096 Jan 25 22:18 dir1
-rw-r--r-- 1 elliot elliot 0    Jan 25 23:08 file1
-rw-r--r-- 1 elliot elliot 0    Apr 11  2010 file2
-rw-r--r-- 1 elliot elliot 0    Oct 3   1998 file3
elliot@ubuntu-linux:~$ ls -l -u 
total 8 
drwxr-xr-x 6 elliot elliot 4096 Jan 25 22:13 Desktop
drwxr-xr-x 3 elliot elliot 4096 Jan 25 22:18 dir1
-rw-r--r-- 1 elliot elliot 0    Feb 29 2004  file1
-rw-r--r-- 1 elliot elliot 0    Apr 11 2010  file2
-rw-r--r-- 1 elliot elliot 0    Oct 3  1998  file3

As you can see, the last modification time of file1 is changed to Jan 25 23:08, but the access time is left unchanged: Feb 29 2004. Now this time around, let's only change the access time of file2. To do this, we pass the -a option to the touch command:

elliot@ubuntu-linux:~$ touch -a file2 
elliot@ubuntu-linux:~$ ls -l
total 8
drwxr-xr-x 6 elliot elliot 4096 Jan 25 22:13 Desktop
drwxr-xr-x 3 elliot elliot 4096 Jan 25 22:18 dir1
-rw-r--r-- 1 elliot elliot    0 Jan 25 23:08 file1
-rw-r--r-- 1 elliot elliot    0 Apr 11  2010 file2
-rw-r--r-- 1 elliot elliot    0 Oct  3  1998 file3 
elliot@ubuntu-linux:~$ ls -l -u
total 8
drwxr-xr-x 6 elliot elliot 4096 Jan 25 22:13 Desktop
drwxr-xr-x 3 elliot elliot 4096 Jan 25 22:18 dir1
-rw-r--r-- 1 elliot elliot   0  Feb 29  2004 file1
-rw-r--r-- 1 elliot elliot   0  Jan 25 23:20 file2
-rw-r--r-- 1 elliot elliot   0  Oct  3  1998 file3 
elliot@ubuntu-linux:~$

As you can see, the modification time of file2 was left unchanged, but the access time is changed to the current time. Now to change both the modification and access times of file3, you can run the touch command with no options:

elliot@ubuntu-linux:~$ ls -l file3
-rw-r--r-- 1 elliot elliot 0 Oct 3 1998 file3 
elliot@ubuntu-linux:~$ touch file3 
elliot@ubuntu-linux:~$ ls -l file3
-rw-r--r-- 1 elliot elliot 0 Jan 25 23:27 file3 
elliot@ubuntu-linux:~$ ls -l -u file3
-rw-r--r-- 1 elliot elliot 0 Jan 25 23:27 file3

Awesome! You can also pass the -t option to the ls command to list the files sorted by modification times, newest first:

elliot@ubuntu-linux:~$ ls -l -t 
total 8
-rw-r--r-- 1 elliot elliot    0 Jan 25 23:27 file3
-rw-r--r-- 1 elliot elliot    0 Jan 25 23:08 file1
drwxr-xr-x 3 elliot elliot 4096 Jan 25 22:18 dir1
drwxr-xr-x 6 elliot elliot 4096 Jan 25 22:13 Desktop
-rw-r--r-- 1 elliot elliot    0 Apr 11  2010 file2

You can add the -u option to sort by access times instead:

elliot@ubuntu-linux:~$ ls -l -t -u 
total 8
-rw-r--r-- 1 elliot elliot    0 Jan 25 23:27 file3
-rw-r--r-- 1 elliot elliot    0 Jan 25 23:20 file2
-rw-r--r-- 1 elliot elliot    0 Jan 25 23:20 file1
drwxr-xr-x 3 elliot elliot 4096 Jan 25 22:18 dir1
drwxr-xr-x 6 elliot elliot 4096 Jan 25 22:13 Desktop

You can also pass the -r option to reverse the sorting:

elliot@ubuntu-linux:~$ ls -l -t -r 
total 8
-rw-r--r-- 1 elliot elliot    0 Apr 11  2010 file2
drwxr-xr-x 6 elliot elliot 4096 Jan 25 22:13 Desktop
drwxr-xr-x 3 elliot elliot 4096 Jan 25 22:18 dir1
-rw-r--r-- 1 elliot elliot    0 Jan 25 23:08 file1
-rw-r--r-- 1 elliot elliot    0 Jan 25 23:27 file3

To create directories in Linux, we use the mkdir command, which is short for make directory.

In elliot's desktop, let's create a directory named games by running the mkdir games command:

elliot@ubuntu-linux:~/Desktop$ mkdir games 
elliot@ubuntu-linux:~/Desktop$ ls -l 
total 8
drwxr-xr-x 2 elliot elliot 4096 Jan 20 20:20 games
-rw-r--r-- 1 elliot elliot 37 Jan 19 14:20 hello.txt 
elliot@ubuntu-linux:~/Desktop$

Notice that my current working directory is /home/elliot/Destkop; that's why I was able to use a relative path.

You can also create multiple directories at the same time. For example, you can create three directories – Music, Movies, and Books – on your desktop by running the mkdir Music Movies Books command:

elliot@ubuntu-linux:~/Desktop$ mkdir Music Movies Books 
elliot@ubuntu-linux:~/Desktop$ ls -l
total 20
drwxr-xr-x 2 elliot elliot 4096 Jan 21 01:54 Books
drwxr-xr-x 2 elliot elliot 4096 Jan 20 20:20 games
-rw-r--r-- 1 elliot elliot   37 Jan 19 14:20 hello.txt
drwxr-xr-x 2 elliot elliot 4096 Jan 21 01:54 Movies
drwxr-xr-x 2 elliot elliot 4096 Jan 21 01:54 Music

You can also use the -p option to create a whole path of directories. For example, you can create the path /home/elliot/dir1/dir2/dir3 by running the mkdir -p dir1/dir2/dir3 command:

elliot@ubuntu-linux:~$ pwd
/home/elliot
elliot@ubuntu-linux:~$ mkdir -p dir1/dir2/dir3 
elliot@ubuntu-linux:~$ ls 
blabla Desktop dir1 
elliot@ubuntu-linux:~$ cd dir1 
elliot@ubuntu-linux:~/dir1$ ls 
dir2
elliot@ubuntu-linux:~/dir1$ cd dir2 
elliot@ubuntu-linux:~/dir1/dir2$ ls 
dir3
elliot@ubuntu-linux:~/dir1/dir2$ cd dir3 
elliot@ubuntu-linux:~/dir1/dir2/dir3$ pwd
/home/elliot/dir1/dir2/dir3 
elliot@ubuntu-linux:~/dir1/dir2/dir3$

It created dir1 in the /home/elliot directory, and then it created dir2 inside of dir1, and finally, it created dir3 inside of dir2.

You can use the recursive -R option to do a recursive listing on /home/elliot/dir1 and see all the files underneath /home/elliot/dir1 without the hassle of changing to each directory:

elliot@ubuntu-linux:~$ ls -R dir1 
dir1:
dir2

dir1/dir2:
dir3

dir1/dir2/dir3: 
elliot@ubuntu-linux:~$

As you can see, it listed all the files under /home/elliot/dir1. It even displayed the hierarchy.

You can also create a new directory with multiple subdirectories by including them inside a pair of curly brackets and each subdirectory separated by a comma like in the following:

elliot@ubuntu-linux:~/dir1/dir2/dir3$ mkdir -p dir4/{dir5,dir6,dir7} 
elliot@ubuntu-linux:~/dir1/dir2/dir3$ ls -R dir4
dir4:
dir5 dir6 dir7 

dir4/dir5: 

dir4/dir6:
 
dir4/dir7:

As you can see, we created dir4, and inside it, we created three directories – dir5, dir6, and dir7.

You have learned a lot of different options that you can use with the ls command. Table 4 summarizes all the options we have used so far.

You will often be wanting to use two or more command options at a time. For example, ls -a -l is commonly used to do a long listing for all the files in a directory.

Also, ls -l -a -t -r is a very popular combination because sometimes you would want to see the listing of the files sorted by modification times (oldest first). For that reason, combining the command options is more efficient and so running the ls -latr command:

elliot@ubuntu-linux:~$ ls -latr 
total 120
-rw-r--r--  1 elliot elliot       0    Apr 11  2010 file2
-rw-r--r--  1 elliot elliot     807    Dec 26 23:47 .profile
-rw-r--r--  1 elliot elliot    3771    Dec 26 23:47 .bashrc
drwxr-xr-x  9 root   root      4096    Jan 17 04:37 ..
-rw-r--r--  1 elliot elliot     220    Jan 20 17:23 .bash_logout
drwxr-xr-x  6 elliot elliot    4096    Jan 25 22:13 Desktop
-rw-r--r--  1 elliot elliot       0    Jan 25 23:08 file1
-rw-r--r--  1 elliot elliot       0    Jan 25 23:27 file3
drwxr-xr-x  3 elliot elliot    4096    Jan 25 23:52 dir1
-rw-------  1 elliot elliot    3152    Jan 26 00:01 .bash_history
drwxr-xr-x 17 elliot elliot    4096    Jan 30 23:32 .

Will yield the same result as running the ls -l -a -t -r command:

elliot@ubuntu-linux:~$ ls -l -a -t -r 
total 120
-rw-r--r--  1 elliot elliot    0 Apr 11  2010 file2
-rw-r--r--  1 elliot elliot  807 Dec 26 23:47 .profile
-rw-r--r--  1 elliot elliot 3771 Dec 26 23:47 .bashrc
drwxr-xr-x  9 root   root   4096 Jan 17 04:37 ..
-rw-r--r--  1 elliot elliot  220 Jan 20 17:23 .bash_logout
drwxr-xr-x  6 elliot elliot 4096 Jan 25 22:13 Desktop
-rw-r--r--  1 elliot elliot    0 Jan 25 23:08 file1
-rw-r--r--  1 elliot elliot    0 Jan 25 23:27 file3
drwxr-xr-x  3 elliot elliot 4096 Jan 25 23:52 dir1
-rw-------  1 elliot elliot 3152 Jan 26 00:01 .bash_history
drwxr-xr-x 17 elliot elliot 4096 Jan 30 23:32 .

Before this chapter comes to an end, I want to show you a pretty cool tip. First, let's create a directory named averylongdirectoryname:

elliot@ubuntu-linux:~$ mkdir averylongdirectoryname 
elliot@ubuntu-linux:~$ ls -ld averylongdirectoryname
drwxr-xr-x 2 elliot elliot 4096 Mar 2 12:57 averylongdirectoryname

Tab Completion is one of the most useful features in the Linux command line. You can use this to feature to let the shell automatically complete (suggest) command names and file paths. To demonstrate, type (don't run) the following text on your terminal:

elliot@ubuntu-linux:~$ cd ave

Now press the Tab key on your keyboard, and the shell will automatically complete the directory name for you:

elliot@ubuntu-linux:~$ cd averylongdirectoryname/

Pretty cool! Alright, this takes us to the end of this chapter, and it's time for you to do the lovely knowledge check.

For the following exercises, open up your terminal and try to solve the following tasks:

1. Do a long listing for all the files in /var/log.
2. Display the contents of the file /etc/hostname.
3. Create three files – file1, file2, and file3 – in /home/elliot.
4. List all the files (including hidden files) of elliot's home directory.
5. Create a directory named fsociety in /home/elliot.

True or false

1. /home/root is the home directory of the root user.
2. dir1/dir2/dir3 is an example of an absolute path.
3. /home/elliot/Desktop is an example of an absolute path.
4. touch -m file1 will update file1 access time.
5. mkdir dir1 dir2 dir3 will create three directories – dir1, dir2, and dir3.