Linux 101 (Part 1): Introduction
Learn Linux CLI the Right Way
Objective
Welcome to "Linux 101," a comprehensive series designed to transform beginners into confident Linux command line users. In today's digital infrastructure, Linux powers everything from web servers and cloud platforms to network devices and security systems, making command line proficiency an essential skill for IT every professionals.
The command line interface (CLI) is the heart of Linux systems. While graphical interfaces offer convenience, the CLI provides unparalleled power, efficiency, and automation capabilities that are critical for:
Network engineers
System administrators
Security professionals
DevOps engineers
Cloud specialists
Your First Linux Commands
One of the primary motivations for someone to transition to Linux is to take advantage of what is arguably its most powerful feature: the terminal!
At one point, the entire Linux operating system operated solely through the terminal, but today, numerous graphical tools have been created, leading to the development of stunning desktop environments like Ubuntu.
Fundamentally the main difference between using the terminal and using normal graphical methods that you probably already familiar with from using Windows or MAC, instead of pointing and clicking with mouse to control your computer, you will be typing commands with keyboard instead.
Linux is unique and the development of Linux is closely tied to the terminal and this means knowing how to use the terminal gives you pretty much absolute control of how your computer works, by using the terminal you can do pretty much anything you want with your Linux computer that you cannot get this level of control of any other operating system, making mastering the terminal an invaluable skill.
Let's open the terminal and begin typing some commands to see their effects! The goal here is simply to get familiar with the interface, understand what the terminal looks like, and see how it responds to our commands. From there, we can proceed further.
“CTRL+ALT+T “ this is the shortcut you will use to open the terminal on your ubuntu machine
Everything in Linux is case sensitive, so pay extra attention when you are typing any command
Let’s start with fun command, “echo”
The “echo” command just print on the screen what you give it as an input!
root@vps004:~# echo Hello World!
Hello World!
root@vps004:~# echo Hellooooooo
Hellooooooo
root@vps004:~# let’s try now with another command called “cal”
The “cal” command is going to show you a calendar on the screen!
root@vps004:~# cal
April 2025
Su Mo Tu We Th Fr Sa
1 2 3 4 5
6 7 8 9 10 11 12
13 14 15 16 17 18 19
20 21 22 23 24 25 26
27 28 29 30 This is just the default behavior of the “cal” command, prints calendar of the current month, with todays date highlighted, however what make Linux commands interesting is that you can customize the behavior of commands to do what you want them to do.
for example, let’s say we want to see the calendar not just for the current month, but for the current year! so our command now will be “cal 2025”
root@vps004:~# cal 2025
2025
January February March
Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa
1 2 3 4 1 1
5 6 7 8 9 10 11 2 3 4 5 6 7 8 2 3 4 5 6 7 8
12 13 14 15 16 17 18 9 10 11 12 13 14 15 9 10 11 12 13 14 15
19 20 21 22 23 24 25 16 17 18 19 20 21 22 16 17 18 19 20 21 22
26 27 28 29 30 31 23 24 25 26 27 28 23 24 25 26 27 28 29
30 31
April May June
Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa
1 2 3 4 5 1 2 3 1 2 3 4 5 6 7
6 7 8 9 10 11 12 4 5 6 7 8 9 10 8 9 10 11 12 13 14
13 14 15 16 17 18 19 11 12 13 14 15 16 17 15 16 17 18 19 20 21
20 21 22 23 24 25 26 18 19 20 21 22 23 24 22 23 24 25 26 27 28
27 28 29 30 25 26 27 28 29 30 31 29 30
July August September
Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa
1 2 3 4 5 1 2 1 2 3 4 5 6
6 7 8 9 10 11 12 3 4 5 6 7 8 9 7 8 9 10 11 12 13
13 14 15 16 17 18 19 10 11 12 13 14 15 16 14 15 16 17 18 19 20
20 21 22 23 24 25 26 17 18 19 20 21 22 23 21 22 23 24 25 26 27
27 28 29 30 31 24 25 26 27 28 29 30 28 29 30
31
October November December
Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa
1 2 3 4 1 1 2 3 4 5 6
5 6 7 8 9 10 11 2 3 4 5 6 7 8 7 8 9 10 11 12 13
12 13 14 15 16 17 18 9 10 11 12 13 14 15 14 15 16 17 18 19 20
19 20 21 22 23 24 25 16 17 18 19 20 21 22 21 22 23 24 25 26 27
26 27 28 29 30 31 23 24 25 26 27 28 29 28 29 30 31
30 Also, we can give our commands something called “an option” which is something allow you to customize the behavior of the command. So instead of typing “cal 2025” we can add the option “-y” to the command which achieve the same thing, printing the entire current year on the screen.
root@vps004:~# cal -y
2025
January February March
Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa
1 2 3 4 1 1
5 6 7 8 9 10 11 2 3 4 5 6 7 8 2 3 4 5 6 7 8
12 13 14 15 16 17 18 9 10 11 12 13 14 15 9 10 11 12 13 14 15
19 20 21 22 23 24 25 16 17 18 19 20 21 22 16 17 18 19 20 21 22
26 27 28 29 30 31 23 24 25 26 27 28 23 24 25 26 27 28 29
30 31
April May June
Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa
1 2 3 4 5 1 2 3 1 2 3 4 5 6 7
6 7 8 9 10 11 12 4 5 6 7 8 9 10 8 9 10 11 12 13 14
13 14 15 16 17 18 19 11 12 13 14 15 16 17 15 16 17 18 19 20 21
20 21 22 23 24 25 26 18 19 20 21 22 23 24 22 23 24 25 26 27 28
27 28 29 30 25 26 27 28 29 30 31 29 30
July August September
Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa
1 2 3 4 5 1 2 1 2 3 4 5 6
6 7 8 9 10 11 12 3 4 5 6 7 8 9 7 8 9 10 11 12 13
13 14 15 16 17 18 19 10 11 12 13 14 15 16 14 15 16 17 18 19 20
20 21 22 23 24 25 26 17 18 19 20 21 22 23 21 22 23 24 25 26 27
27 28 29 30 31 24 25 26 27 28 29 30 28 29 30
31
October November December
Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa
1 2 3 4 1 1 2 3 4 5 6
5 6 7 8 9 10 11 2 3 4 5 6 7 8 7 8 9 10 11 12 13
12 13 14 15 16 17 18 9 10 11 12 13 14 15 14 15 16 17 18 19 20
19 20 21 22 23 24 25 16 17 18 19 20 21 22 21 22 23 24 25 26 27
26 27 28 29 30 31 23 24 25 26 27 28 29 28 29 30 31
30 To summarize, you can customize the behavior of commands using:
input —> cal 2025
option —> cal -y
we will be going into more depth about command “inputs” and “options” in a lot more detail, but we are going to save this for later. As for now we are just experiencing the CLI, typing some basic commands and get comfortable with the terminal.
The “date” command is straightforward to check today’s date!
root@vps004:~# date
Sat 05 Apr 2025 02:35:19 PM UTCThe “clear” command
this command simply clear your terminal by removing all the previous text from the screen, there is keyboard shortcut for it “CTRL+L”
If you press the up arrow key, you will see the most recent command you have typed, keep pressing that for older commands.
you can also look at your whole command history using “history” command
root@vps004:~# history
1 history
2 clear
3 shell
4 clear
5 echo $PATH
6 efiwefjowe
7 clear
8 ech $PATH
9 echo $PATH
10 which echo
11 cd /usr/bin/
12 ls
13 cd
14 ls -la
15 cd /usr/bin/
16 ls
17 cd echo
18 cat echo
19 clear
20 cd ..
21 exit
22 history
23 which cal
24 cd /usr/bin
25 ls
26 cd root
27 cd ..
28 ls
29 which which
30 date
31 clear
32 cal 8 2020
33 cal 12 2020
34 cal 2 2026
35 cal march 2020
36 clear
37 date
38 date -u
39 cal dec 2020
40 cal -A 1 dec 2020
41 cal -A 3 dec 2020we can see all the previous commands that I have typed in my terminal, even if the command was wrong it will be saved here in the history, with each command you can see a “line number” associated with it.
for example, we can see the line number = 37 " for the date command, let’s say I want to run the “date” command again, instead of cycling all the way back to “date” command using the up arrow key, I can do this instead “! + line number”:
root@vps004:~# !37
date
Sat 05 Apr 2025 02:47:29 PM UTCand if you just want to run the most recent command you have typed you can use “!!”
root@vps004:~# !!
date
Sat 05 Apr 2025 02:49:35 PM UTCsince that last command I used was the “date” command, when I typed “!!” I got the same result, printing the today’s date on the screen.
sometimes this history file that stores your commands can get quite long, so if you want to clear the history, it’s kind of tow step process “history -c ; history -w” and what this does, is the “-c” opting clears the history while the “-w” option write those changes:
root@vps004:~# history -c ; history -w
root@vps004:~# history
1 history
root@vps004:~# finally to close the terminal, you can use the “exit” command or use the keyboard shortcut of “CTRL+ALT+D”
Summary
The use case of the commands we discussed earlier may not be entirely clear at this moment, and that’s perfectly fine. Our goal in this section wasn't to learn all the available commands at once; rather, we aimed to simply enter our initial commands in the terminal and observe the results on our screen.
All commands in the Linux CLI share a somewhat similar structure, and grasping that structure is a crucial step towards mastering the CLI and harnessing the power of the terminal. In the next section, we will explore how Linux commands are structured, which serves as a vital foundation step for everything we'll learn moving forward. If you have previously used Linux but never felt confident in your understanding, or if you're new to Linux, then the next section is an excellent place to start.
