Linux Fundamentals Part 2

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Task 1: Introduction

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

• Unlocking the potential of our first few commands by introducing flags and arguments

• Advancing our knowledge of the filesystem by copying and moving files

• Discovering how access to files and folders is managed and how we can determine our access

• Running our first few scripts and executables

Task 2: Accessing Your Linux Machine Using SSH (Deploy)

Secure Shell (SSH) is a protocol between devices in an encrypted form. We can SSH into the machine for this room using the command ssh tryhackme@<machine_ip>. The machine IP is listed at the top of the page after we start the machine for the room.

Task 3: Introduction to Flags and Switches

Commands in Linux have a default behavior. For example, ls lists the contents of the working directory. We can add flags to commands to extend the behavior of commands. man <command> can be used to view the associated flags for each command.

What directional arrow key would we use to navigate down the manual page?

down

Pressing the down key scrolls the manual page down, and pressing the up key scrolls up.

What flag would we use to display the output in a "human-readable" way?

-h

Use the command man ls to view the flags for ls. Then, press the down key to find the flag that results in "human-readable" output.

Task 4: Filesystem Interaction Continued

The command line can also be used to manipulate files. touch <file> creates a new file and mkdir <directory> creates a new folder. Files and folders can be copied with cp <file> <destination>, moved with mv <file> <destination>, and removed with rm <file>. file <file> can be used to output the file type.

How would you create the file named "newnote"?

touch newnote

The touch command is used to create a new file.

On the deployable machine, what is the file type of "unknown1" in "tryhackme's" home directory?

ASCII text

Use the file command to view the file's type.

How would we move the file "myfile" to the directory "myfolder"

mv myfile myfolder

The mv command is used to move or rename a file.

What are the contents of this file?

THM{FILESYSTEM}

Use cat myfile to output the contents of the file to the command line.

Task 5: Permissions 101

In Linux, a file's characteristics determines what actions can be performed on that file and by whom. The three basic actions we have in Linux are read, write and execute.

A file's permissions can be viewed by using the -l flag on the ls command.

We can switch users using su <user>.

On the deployable machine, who is the owner of "important"?

user2

Use ls -l to view the owner of "important".

What would the command be to switch to the user "user2"?

su user2

The su command is used to switch users.

Output the contents of "important", what is the flag?

THM{SU_USER2}

After switching to user2 using su, we can cat to view the output of "important".

Task 6: Common Directories

The Linux filesystem is organized into directories that hold important files for the operating system. The /etc directory holds system files that are used by the operating system. /var holds variable data such as logs. /root is the home directory for the root user, and /tmp holds temporary information and is wiped after the computer is restarted.

What is the directory path that would we expect logs to be stored in?

/var/log

Logs are stored in the log directory of /var.

What root directory is similar to how RAM on a computer works?

/tmp

RAM on a computer is wiped after the computer is restarted, similar to tmp.

Name the home directory of the root user

/root

The root user's home directory is simply root.

Task 7: Conclusions and Summaries

In conclusion, this room allowed us to:

• Use terminal text editors

• Deploy general utilities, such as downloading and serving contents using a Python web server

• Take a look into processes

• Maintain and automate our system using crontabs, package management, and reviewing logs

Task 8: Linux Fundamentals Part 3

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

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