Linux Fundamentals Part 3
TryHackMe Walkthroughs â‹… Guided â‹… Linux Fundamentals Part 3
Between the time I finished this room and the time I wrote this walkthrough, this room has unfortunately become premium-access only. I've constructed this walkthrough based on my personal notes, but I now lack access to the original room. So, please let me know if this walkthrough has any inaccuracies.
Task 1: Introduction
In this room, we will learn about automation, package management, and service/application logging.
Task 2: Deploy Your Linux Machine
To complete this room, we first need to deploy and log into the room's associated machine.
Task 3: Terminal Text Editors
We can edit files with terminal text editors like Nano and Vim.
nano <file> can be used to open or create a file in the text editor. Pressing [CTRL] + [X] on our keyboard will allow us to exit nano.
Vim is a much more advanced text editor. Learning Vim is much more difficult than learning Nano, but Vim offers advanced features and customizability that Nano does not have.
Task 4: General/Useful Utilities
We can download files from the web via HTTP using wget <address>. We can copy files and folders between our local system and a remote system using secure copy. scp <local_file> <remote_user>@<remote_destination>:<remote_file> copies from our system to the remote system where remote_file specifies the name that we wish to store the file as on the remote system. scp <remote_user>@<remote_destination>:<remote_file> <local_file> copies from the remote system to our system where local_file specifies the name that we wish to store the file as on our local system.
Python3's "HTTPServer" allows us to serve files on the web and can be run with the command python3 -m http.server.
Task 5: Processes 101
Processes are the programs that are running on a machine. They are managed by the kernel, where each process will have an ID associated with it, also known as its PID. PIDs are assigned by the order in which a process starts. Processes with a PID of 0 are started when the system boots.
ps can be used to view processes running as our user session. ps aux includes processes run by other users and system processes.
ps gives a one-time view of processes. In contrast, top can be used to see real-time statistics about the processes running on a system.
We can send signals to processes in order to terminate them. Consider these three signals:
SIGTERM allows a process to do some cleanup tasks and then kills the process.
SIGKILL kills the process without any cleanup afterwards.
SIGSTOP stops or suspends a process.
A computer's operating system uses namespaces to split up the computer's resources, such as CPU and RAM. Namespaces help isolate processes from one another.
One of the first processes that starts when a computer boots is systemd. systemctl <option> <service> allows to interact with the systemd process. The four options we can use with this command are start, stop, enable, and disable.
Processes can either run in the foreground or in the background. Processes that run in the background allow us to continue running further commands while waiting for that process to complete. A process can be backgrounded by adding the & operator to the command. A backgrounded process can be brought back to the foreground using fg.
Task 6: Maintaining Your System: Automation
We can schedule certain tasks to occur after every system boot using the cron process. We interact with this process by writing crontabs, or special files that are executed by the cron process.
Task 7: Maintaining Your System: Package Management
Software on Linux can be downloaded and managed with the Advanced Package Tool (apt). We can download packages with apt-get install <package> and remove packages with apt-get remove <package>.
Task 8: Maintaining Your System: Logs
As noted in Linux Fundamentals Part 1, logs are located in the /var/log folder in Linux. Consider the following three services:
Apache2 is a web server.
fail2ban monitors attempted brute force attempts.
UFW is used as a firewall.
The logs for these services will contain a wealth of information about what actions users are taking on a system.
Task 9: Conclusions & Summaries
In conclusion, this room taught us:
How to use terminal text editors
General utilities such as downloading and serving contents using a Python web server
The basics of processes
How to maintain and automate a system using crontabs, package management, and reviewing logs
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