Linux Fundamentals Full Course | TryHackMe Linux Fundamentals

Introduction

We covered the second volume of basics and fundamentals of Linux operating system. We covered permissions, processes, services, files and directories, downloading and uploading, system configurations,etc. This was part of Pre Security pathway and TryHackMe Linux Fundamentals Room.

OSCP Study Notes

CompTIA Security+ SY0-601 Study Notes

The video begins by explaining that the content will focus on Linux basics as laid out in TryHackMe’s pre-security path.It emphasizes that the video will not go into deep reading of materials but will instead focus on answering questions and explaining how to approach them.

Basic Linux Commands

Echo Command:

• The instructor explains how to use echo to display text in the terminal (e.g., echo "TryHackMe").
• They show how echo can be used to write text to a file, for example: echo "TryHackMe" > file1.

ID Command:

• The id command is used to display the current user’s ID and group information.

Hostname Command:

• The hostname command shows the name of the machine.

Man Pages:

• Man pages provide detailed information about commands and their usage. The instructor emphasizes the importance of using man <command> (e.g., man cat) to explore the different options and flags that a command supports.

Cat Command:

• The cat command is used to display the contents of files in the terminal. The video demonstrates how cat works with a file named test.txt and explains that cat is useful for viewing text-based content quickly.

LS Command:

• ls is used to list files and directories in the current directory. The instructor goes further by explaining options like ls -a to display hidden files and ls -l for long format listing, which shows details like permissions and ownership of files.
• Directories are identified by the “d” at the beginning of the permissions string, while regular files do not have the “d.”

Touch Command:

• touch is used to create empty files. The instructor demonstrates creating a file named test2.txt using touch test2.txt and verifying it with the ls command.

Executing Binaries:

• Binary files are executable files in Linux. The instructor explains how to check the nature of a file using the file command (e.g., file shiva2).
• Two ways to execute binaries are discussed:
  • Absolute Path: Providing the full path to the binary (e.g., /home/user/shiva2).
  • Relative Path: Using ./binaryname to execute the binary from the current directory.

Changing Users:

• The su command allows switching to another user. For example, su root switches to the root user, provided the user knows the root password. The instructor explains the differences between switching users with su alone and su <username>.

Linux File System

pwd Command:

• This command is used to print the current working directory.

ls Command:

• Lists the contents of the current directory.

cd Command:

• Used to change directories.

The instructor shows how to differentiate between directories and files using ls -la and explains how directories are marked with a “d” in their permissions.cat Command:

• The cat command is used to display the contents of a file in the terminal.

Searching for Files in Linux

grep Command:

• grep is used to search for specific patterns or strings in files. In this case, the instructor demonstrates how to use grep to find a flag within an access log file by searching for the prefix “THM

Shell Operators

Redirection Operators:

• The video explains the difference between single (>) and double (>>) arrows for file redirection.
• Single arrows overwrite file contents, while double arrows append to the file without removing the existing content.

Background Processes:

• The & operator is used to run a process in the background, allowing the user to continue using the terminal while the command executes.
• Additionally, the instructor mentions that Ctrl+Z can be used to send a process to the background.

Example: Using Echo and Redirection

The instructor demonstrates how to use echo to replace or append content to a file, showing the difference between single and double redirection arrows.

Practical Examples

Using echo to display and write text.Navigating the file system with cd, pwd, ls.Searching for strings with grep.Redirection with > and >>.Running commands in the background using &.

Room Answers | TryHackMe Linux Fundamentals

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