AWS Solutions Architect · Module 4 · Day 11

Linux Introduction & Navigation Commands

⏱ 13 min read🎯 Beginner friendly🖼 2 diagrams🧪 2 live demos

You are logged in to a Linux server. Now what? This lesson teaches you to read the prompt, become root safely, understand the directory tree and move around. Every command can be tried in the practice terminal below, so you can learn without breaking anything.

In this session

Why Linux, and default users per distribution
Reading the prompt: user, host, directory, $ or #
Switching users: sudo -i, exit, whoami
/ vs /root vs ~ (the three that confuse everyone)
pwd, cd, ls, ll, clear, history
A practice terminal

01Why Linux?

Linux is a free, open-source operating system. It runs most of the world’s servers and most EC2 instances because it is free, stable, secure and light. On servers it is used through the command line.

Distribution	Default EC2 user
Amazon Linux	ec2-user
Ubuntu	ubuntu
RHEL (Red Hat)	ec2-user
SUSE	ec2-user
Debian	admin
Fedora	fedora
Every Linux system	also has the super-user root

02Reading the prompt

ubuntu@ip-172-31-11-229:~$ broken into its four parts.

Command	What it does
`whoami`	which user am I?
`sudo -i` or `sudo su -`	become root with a fresh login (go to /root); $ becomes #
`sudo su`	become root, stay in the same folder
`exit` or Ctrl + D	go back to the previous user
`sudo <command>`	run just one command as root (best practice)

🔑

sudo = borrowing the manager’s master key. You are an employee ($). For one task you borrow the master key (#). Give it back (exit) when done.

03The directory tree

The Linux file system is an upside-down tree starting at /. Note: “/” (root directory) and “/root” (root user’s home) are different things.

Name	Path	Shortcut
Root directory	/	/
Your home	/home/ubuntu	~ (when you are ubuntu)
Root user’s home	/root	~ (when you are root)

04Navigation commands

Command	Meaning	Example
`pwd`	present working directory: where am I?	/home/ubuntu
`cd /var/log`	change directory (absolute path, starts with /)	go to the logs
`cd log`	relative path, from where you are	from /var
`cd ..`	up one level (parent)	/var/log → /var
`cd` or `cd ~`	go home
`cd -`	back to the previous folder
`ls`	list names
`ls -a`	list all, including hidden (names starting with .)	.bashrc
`ll` / `ls -la`	long list: permissions, owner, size, date
`clear` or Ctrl + L	clear the screen
`history`	show past commands	`!25` re-runs #25

Superpowers: press Tab to auto-complete names and ↑ to repeat earlier commands.

Demo · Practice terminal

Demo · Do it yourself

🎯 Exam corner

$ = normal user, # = root. / = root directory, /root = root’s home, ~ = current user’s home.
Work as a normal user and use sudo only when needed (least privilege).
Check /var/log/cloud-init-output.log to see whether your EC2 user data script ran.

05Summary

Linux runs most cloud servers; default users: ec2-user (Amazon Linux) and ubuntu.
Prompt: user@host:directory$; $ normal, # root.
sudo -i to become root, exit to return, whoami to check.
/ top of the tree, /root root’s home, ~ your home.
pwd, cd, ls -a, ll, clear, history.

06Quick quiz

1. What does # at the end of the prompt mean?

2. Command to become root with a fresh login?

3. Difference between / and /root?

4. You are in /var/log. Where does cd .. take you?

5. Which shows hidden files?

07References

Created by Ajeetkumar