Where is Linux Used?

It’s fair to say that Linux is a lot more intimidating to approach than Operating System’s (OSs) such as Windows. Both variants have their own advantages and disadvantages. For example, Linux is considerably much more lightweight and you’d be surprised to know that there’s a good chance you’ve used Linux in some form or another every day! Linux powers things such as:

Websites that you visit

Car entertainment/control panels

Point of Sale (PoS) systems such as checkout tills and registers in shops

Critical infrastructures such as traffic light controllers or industrial sensors

Flavors of Linux

The name “Linux” is actually an umbrella term for multiple OS’s that are based on UNIX (another operating system). Thanks to Linux being open-source, variants of Linux come in all shapes and sizes – suited best for what the system is being used for.

Running Your First Few Commands

For example, Ubuntu & Debian are some of the more commonplace distributions of Linux because it is so extensible. I.e. you can run Ubuntu as a server (such as websites & web applications) or as a fully-fledged desktop. For this series, we’re going to be using Ubuntu.

Running Your First Few Commands

tryhackme@linux1:~$ echo Hello

Hello

tryhackme@linux1:~$ echo “Hello Friend!”

Hello Friend!

As shown in the terminal above, if we want to “echo” a single word, we don’t need to use double quotes, for example, echo Hello. However, the string should be enclosed within double quotes if one or more spaces are present, for example, echo “Hello Friend!”.

whoami can be used to find the username we are logged in as.

Using whoami to find out the username of who we’re logged in as

tryhackme@linux1:~$ whom

So far we’ve only covered the “echo” and “whoami” commands. Not all that useful when you consider things that we need to do – including navigating the filesystem, read and write to it as well.

In this task, we’re going to be learning the commands so that we can do just that. Just like the previous task, I’ll display the commands in the table in the next heading & show examples of these commands being used.

Listing Files in Our Current Directory (ls)

Before we can do anything such as finding out the contents of any files or folders, we need to know what exists in the first place. This can be done using the “ls” command (short for listing)

Using “ls” to list the contents of the current directory

tryhackme@linux1:~$ ls

‘Important Files’ ‘My Documents’ Notes Pictures

In the screenshot above, we can see there are the following directories/folders:

Important Files

My Documents

Notes

Pictures

Great! You can probably take a guess as to what to expect a folder to contain given by its name.

Pro tip: You can list the contents of a directory without having to navigate to it by using ls and the name of the directory. I.e. ls pictures

Changing Our Current Directory (cd)

Now that we know what folders exist, we need to use the “cd” command (short for change directory) to change to that directory. Say if I wanted to open the “Pictures” directory – I’d do “cd Pictures”. Where again, we want to find out the contents of this “Pictures” directory and to do so, we’d use “ls” again:

Listing our new directory after we have used “cd”

tryhackme@linux1:~/Pictures$ ls

dog_picture1.jpg dog_picture2.jpg dog_picture3.jpg dog_picture4.jpg

In this case, it looks like there are 4 pictures of dogs!

Outputting the Contents of a File (cat)

Whilst knowing about the existence of files is great — it’s not all that useful unless we’re able to view the contents of them.

We will come on to discuss some of the tools available to us that allows us to transfer files from one machine to another in a later room. But for now, we’re going to talk about simply seeing the contents of text files using a command called “cat”.

“Cat” is short for concatenating & is a fantastic way for us to output the contents of files (not just text files!).

In the screenshot below, you can see how I have combined the use of “ls” to list the files within a directory called “Documents”:

Using “ls” to list the contents of the current directory

tryhackme@linux1:~/Documents$ ls

todo.txt

tryhackme@linux1:~/Documents$ cat todo.txt

Here’s something important for me to do later!

We’ve applied some knowledge from earlier in this task to do the following:

Used “ls” to let us know what files are available in the “Documents” folder of this machine. In this case, it is called “todo.txt”.

We have then used cat todo.txt to concatenate/output the contents of this “todo.txt” file, where the contents are “Here’s something important for me to do later!”

Pro tip: You can use cat to output the contents of a file within directories without having to navigate to it by using cat and the name of the directory. I.e. cat /home/ubuntu/Documents/todo.txt

Sometimes things like usernames, passwords (yes – really…), flags or configuration settings are stored within files where “cat” can be used to retrieve these.

Finding out the full Path to our Current Working Directory (pwd)

You’ll notice as you progress through navigating your Linux machine, the name of the directory that you are currently working in will be listed in your terminal.

It’s easy to lose track of where we are on the filesystem exactly, which is why I want to introduce “pwd”. This stands for print working directory.

Using the example machine from before, we are currently in the “Documents” folder — but where is this exactly on the Linux machine’s filesystem? We can find this out using this “pwd” command like within the screenshot below:

Using “pwd” to list the full path of the current directory

tryhackme@linux1:~/Documents$ pwd

/home/ubuntu/Documents

tryhackme@linux1:~/Documents$

Let’s break this down:

We already know we’re in “Documents” thanks to our terminal, but at this point in time, we have no idea where “Documents” is stored so that we can get back to it easily in the future.

I have used the “pwd” (print working directory) command to find the full file path of this “Documents” folder.

We’re helpfully told by Linux that this “Documents” directory is stored at “/home/ubuntu/Documents” on the machine — great to know!

Now in the future, if we find ourselves in a different location, we can just use cd /home/ubuntu/Documents to change our working directory to this “Documents” directory.