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Linux Fundamentals Part 1

TryHackMe Walkthroughs â‹… Guided â‹… Linux Fundamentals Part 1

Task 1: Introduction

This room is the first in a three-part series on Linux fundamentals. This room will have us:

  • Running our very first commands in an interactive Linux machine

  • Learning some essential commands used to interact with the file system

  • Learning how users and groups work on Linux (and why this is important for penetration testing)

Task 2: A Bit of Background on Linux

Linux is an umbrella term for a group of operating systems all based on Unix. We refer to these operating systems as "flavors" of Linux since they have many similarities. Linux operating systems are commonly used for websites, control panels, critical infrastructure, and more.

Research: What year was the first release of a Linux operating system?

1991

This information can be found with a quick Google search. The original Linux kernel was released on September 17, 1991.

Task 3: Interacting With Your First Linux Machine (In-Browser)

We can interact with a Linux machine in TryHackMe by pressing the "Start Machine" button on the top-right of each task.

Task 4: Running Your First few Commands

Two basic commands that can be run in the Linux command line are echo and whoami. echo <text> outputs the text we provide to it. whoami outputs the username we are logged in as.

If we wanted to output the text "TryHackMe", what would our command be?

echo TryHackMe

The echo <text> command outputs the provided text. No quotation marks are needed.

What is the username of who you're logged in as on your deployed Linux machine?

tryhackme

Use the command whoami to see our username.

Task 5: Interacting With the Filesystem!

The Linux command line allows us to interact with the filesystem. cd <directory> allows us to change directories and pwd prints which directory we are currently in.

ls lists the files in the current directory. cat <file1> <file2> stands for concatenate. The number of files provided to this command can vary since cat outputs the given files concatenated together. Despite its name, this command is most commonly used to print the contents of a single file.

On the Linux machine that you deploy, how many folders are there?

4

Use the ls command to list files and folders.

Which directory contains a file?

folder4

Use the cd <directory> to enter each folder. Use cd ../ to go "back" one folder.

What is the contents of this file?

Hello World

Use cat <file> to view file contents.

Use the cd command to navigate to this file and find out the new current working directory. What is the path?

/home/tryhackme/folder4

Use pwd to print the directory we are currently in.

Task 6: Searching for Files

We can search the filesystem for files by name or other attributes with find. grep <pattern> <file> can be used to search the contents of files for specific values.

Use grep on "access.log" to find the flag that has a prefix of "THM". What is the flag?

THM{ACCESS}

Use grep THM* access.log to search for prefixes of "THM". The * in the pattern is a wildcard that matches any character.

Task 7: An Introduction to Shell Operators

Various operators in the Linux command line allow us to use commands with more flexibility. & allows us to run commands in the background of our terminal. && looks similar but is unrelated to &. Rather, && allows us to combine multiple commands together in one line of your terminal.

The> operator is a redirector, meaning that we can take the output from a command (such as using cat to output a file) and direct it elsewhere. >> has the same functionality as the > operator but appends the output rather than replacing (meaning nothing is overwritten).

If we wanted to run a command in the background, what operator would we want to use?

&

Running a command in the background is done with <command> &.

If I wanted to replace the contents of a file named "passwords" with the word "password123", what would my command be?

echo password123 > passwords

> is used to write a command's output to a file.

Now if I wanted to add "tryhackme" to this file named "passwords" but also keep "passwords123", what would my command be

echo tryhackme >> passwords

>> is used to append a command's output to a file.

Task 8: Conclusions & Summaries

In conclusion, this room has allowed us to:

  • Understand why Linux is so commonplace today

  • Interact with our first-ever Linux machine

  • Run some of the most fundamental commands

  • Get an introduction to navigating around the filesystem and using commands like find and grep to make finding data even more efficient

  • Power up our commands by learning about some of the important shell operators

Task 9: Linux Fundamentals Part 2

My walkthrough for the next room in this Linux introductory series can be found here.

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