Many servers and security tools use Linux. Let’s learn how to use the Linux operating system, a critical skill in cyber security.
It is going to be a 3 part lesson, so let’s start with the first #FromZeroToHacker lesson.
| Table of contents |
| Introduction |
| What I have learnt today? |
| Stats |
| Resources |
Introduction to Linux Fundamentals
For the average user, Linux is Open-Source, easy to adapt, control, and pretty reliable (ask older Windows users if their SO is reliable!). For hacking and penetration testing, Linux also offers a wide range of tools and applications (Kali Linux distro is the first one that comes to mind), and its command line or terminal interface gives us full control of our system.
What I have learnt today?
A bit of background in Linux
Where is Linux used?
Linux powers things such as:
- The websites you visit
- Car entertainment and 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
Flavours of Linux
“Linux” is an umbrella term for multiple OSs that are based on UNIX (another operating system). Thanks to UNIX being open-source, we have many distribution options, each suited best for what we want.
For example, Ubuntu and Debian are commonplace distributions (or distros) of Linux as it is extensible (You can run Ubuntu as a server or as a desktop OS).
Running our first commands
One of the larger “selling” point of using Linux is how lightweight it can be. This comes with some disadvantages: for example, oftentimes there is no GUI (Graphical User Interface) or “Desktop Environment” to interact with the machine, so we need to resort to using what is called the “Terminal”.
The terminal is purely text-based and it may seem intimidating at first, but if we start learning some basic commands, we can become quite familiar with using it.
We can do basic functions such as navigating to files and directories, displaying their contents and creating/deleting files. The commands are self-explanatory…once you learnt them, of course.
For example, echo displays a text provided by us, and whoami tell us which user are we using:
Interacting with the Filesystem
We can and we should be able to navigate the machine we are using without relying on a desktop environment, as we don’t know what OS we are going to use or if it has a GUI. Always we will find a terminal. Always.
For that, we have a series of commands such as ls to list all files and directories, cd to change the current directory, cat to concatenate text or pwd to Print the Working Directory
Listing files in our current directory (ls)
Before doing anything, we need to know the content in the actual directory. This can be done with the ls (or LiSting) command:
As shown, we have an access.log file and 4 folders or directories.
Changing Our Current Directory (cd)
Now that we know there are directories, we can change our current location to one of them. Using cd (Change Directory) we can navigate our machine:
Outputting the Contents of a File (cat)
Knowing that there are files is not enough: We need to view the contents of (all of) them.
cat is short for ConcATenating, and it is used to output the contents of a file. And not only text files!
Finding out the full Path to our Current Working Directory (pwd)
Sometimes we lose track of where we are on a computer by just using the terminal without any GUI, that’s why we can use pwd to find what is the current directory (as pwd stands for Print Working Directory).
Searching for Files
I know you won’t believe me, but one of the redeeming features of Linux is how efficient you can be by using just the terminal.
But you can only be as efficient as you practise and learn more and more commands, and over time, essential commands will become pure muscle memory.
Using Find
The command find let us find a file:
Find manages to find the file, despite being in another folder. But what if we want to find ALL the text files? Let’s move to the root folder and replace ‘note’ with a wildcard (*).
Using Grep
Another utility that is important to learn about is grep. This command allows us to search too, but inside the content of files, for a specific value.
An Introduction to Shell Operators
Even if that wasn’t enough, we can power up our terminal skills with operators. For example: & to run commands in the background of your terminal, && to combine multiple commands together in one line, > to redirect the output from a command elsewhere, and >> that does the same as > but appending the output rather than replacing it (so nothing is overwritten).
Operator “&”
This operator allows us to execute commands in the background. For example, if we want to copy a large file, something that would take a lot of time, blocking the terminal. By using & we can keep working!
Operator “&&”
Despite the ampersand, isn’t related to the previous command. We use && to make a list of commands to run. For example command1 && command2.
One caveat: command2 only will run if command1 was successful.
Operator “>”
This is known as the output redirector. It takes the output from a command we ran and sends the output somewhere else.
One way to use this like this:
Operator “>>”
This is also an output redirector as >. However, it just appends the text, instead of overwriting, or replacing the content, of the current file.
Stats
From 238.382th to 229.009th. Getting better!
Here is also the Skill Matrix:
Resources
Path: Pre Security
Linux Fundamentals
TryHackMe: Linux fundamentals part 1
