DEV Community: Dharamraj Yadav

I Thought I Knew Linux — Then I Actually Learned It (Week 1)

Dharamraj Yadav — Sun, 21 Jun 2026 05:10:22 +0000

The Big Picture

Before you read this doc you must know english is my second language and this doc is have completely my own words not any AI, translator etc.

What an OS really is

An Operating System is software that manage every system resources and it also manage - Hardware, Kernel, and User space.

Kernel mode and User mode

Kernel mode handle every hardware related work and this is only thing that manage hardware. User mode is just showing us to running programs like right now you are in User mode, you never touch any hardware related things.

The Kernel's 4 Jobs

Process Management - Kernel manage every running process.
Memory Management - Kernel decides which process get how much memory.
Device Drivers - This is important job of kernel to manage devices(hardware, virtual).
System Calls - A system call is a how a program asks the kernel to do something fot it.

Users

Users are very important part of the OS bcz it create wall of processes and a single server can manage multiple users.

UID

Every user gets a UID so the kernel identify the user.

root

This is the BOSS of the system he can do anything in the system without any confirmation model and one more thing the root can do anything but it doesn't mean root have kernel mode this is steel in the user mode.

Groups

Every user have a group and we can manage the permissions on the group so we easily add/remove users from group.

The Shell & Basic Commands

What the shell actually is

The shell is a program where we run commands. shell is a interface between kernel and users.

Commands Structure

program + options + argument. ls -l /home
ls - program
-l - option
/home - argument

Core Commands

ls - list the data(files & Directories)
cat - View the inside file
echo - print something
touch - create a file
cp - copy anything
mv - move anything
rm - remove anything(you only remove files & directories that access you have)

Navigation

pwd - present working directory
cd - change directory
mkdir - create directory
rmdir - remove empty directory

Absolute & Relative Path

Absolute path mean full path of the file for example:- /home/user/directory/test.txt

Relative path mean only current folder path for example:- directory/test.txt

Wildcards(globbing)

- ls *.txt(now * mean find only .txt files) ? - ls filen?ame.txt(it mean now the ? find only one single letter)

Intermediate Commands

Searching/Viewing

grep - this cmds grep the exact line what we want(grep "findme" file.txt). -i(case insensitive) and -v(this exclude lines that containing findme) is options of this cmd.
sort - sort lines alphabetically.
head - bydefault print 10 top lines(head filename.txt)
tail - bydefault print 10 bottom lines(tail filename.txt)
less - not print everything in single time it wait for your keys(up, down, q etc.)

Finding/inspecting

find - this find in the subfolders also(but ls find only on the current directory)
locate - quickly find files and direcotries
diff - check differences between two files
file - details of any file

Variables & PATH

Shell Variables & Environment Variables

Shell variable are the private variables of the shell we can't use them in child programs but environment variable can do but before it we need to export that.

How shell finds commands

shell find cmds on the $PATH not in the whole system if sometime the program is installed but the shell throe error like (command not find) it mean that cmd is not in the $PATH

Editing, Help, Input/Output & Errors

Editing in the terminal

vi, vim, nano, these are the terminal editors.(vim filename.txt)
Getting Help: man, man -k, --help. (-k mean search keyword)
Redirection & Pipes: >(> mean overwrite the content), >>(>> mean append the text), | (| mean get output preview cmd)

Processes

What is process

Process is a running instance of the program and every process have a PID(we can kill the process by their PID)

Process Commands

ps: Show running Processes
ps aux: Show running processes with details
kill : kill process by their PID
kill -9 : forcefully kill the process
cmd &: & used for run process in background
ctrl c: stop running process from screen that running right now on screen

File Permissions

When we run the ls -l command you see something like this:-
-rwx-w-rw- 1 username groupname so on....
Breakdown of this:-

-> -(hyphen) mean this is a file rwx - r stand for read, w stand for write, x stand for execute. first 3 letter for owner, then 3 letter for group, and last three letter for others(other users). in our output(-rwx-w-rw-) you see -(hyphen) it mean this is file. then you see rwx it mean owner have read,write,execute permission. then you see (-w-) it mean group have only write permission not read not execute. and last 3(rw-) it mean others have read and write permission not execute.

Change the permission

chmod - it mean change mode so you can change the permissions like chmod 747. each permission have a number:-
read - 4
write - 2
execute - 1
if we want read(4) and write(2) permission to owner just run this command chmod 600. 00 mean no permission to group and other.
and we use something like chmod u+x, u+r. it mean please add execute and read permission for user(owner).

Symbolic Links

Symbolic link just like shortcut in window and alias in mac.
Commands for linux:-
ln -s target linkname
the -s stand for symbolic link OR soft link.

Archiving

tar command

tar mean bundle of the files & directories.
if you want to create a bundle just run this cmd:- tar -czf filename.tar yourstuffs
Options of the cmd:-
-czf - mean create
-tzf - mean show the list inside bundle
-xzf - mean extract the bundle

gzip command

gzip mean compress the file size of the bundle. it only used for create bundle + compress the size.
.tar.gz

Filesystem in Linux

In linux root you see this directories:-
etc, home, var, usr, tmp etc.

etc

This directory have only configuration related data.

home

This is only for users. how many users with there personal data.

var

This directory for the logs of the system and logs are inside /var/log

usr

This directory have most installed programs and /usr/bin have linux commands.

tmp

This directory have temporary data as it name.

Running Commands as super user(sudo)

Every linux user should know about this topic. coz it is very important to know. in linux you can't delete,view,run anything without permission and every user have permissions to what to do or not. some users have sudo access it mean they can install, delete anything in system without any permission bcz they have root access sudo stand for super user.

My First CI/CD Pipeline with YAML and Docker on AWS

Dharamraj Yadav — Tue, 17 Mar 2026 13:41:32 +0000

Hello everyone, today I want to share how I added my first CI/CD pipeline using YAML and Docker on AWS. First, I forked a React project on my GitHub because I didn’t want to waste time setting up React and adding a very simple app, so I decided to fork a project. Then I cloned that repository and added .dockerignore and Dockerfile files in my project’s root directory, and this is the code you can see in the screenshots:

After that, I created an EC2 instance to run my project and installed Docker. I added my Ubuntu user to Docker because Docker runs as root and the Ubuntu user doesn’t have access to that, so I added the user to the Docker group. Look at the screenshot I attached:

After that, I worked on the YAML for CI/CD. I created a .github folder in the root directory of my project, then created another folder called workflows, and in this folder I created a deploy.yml file. In this file, first I added the project name, after that I added on for when I push code to the main branch, then it triggers the action, and in the last I added my jobs. First, I used Ubuntu, then I checked out the code in that Ubuntu machine. After that, I copied this code to my EC2 machine, then SSH into my Ubuntu machine, then cd into my project, stop the running Docker container, build a new one, and run it. When I pushed the code, I saw my project was still not running, then I added an inbound rule in my EC2 machine because by default EC2 blocks other access points, so I added an inbound rule so everyone can access it.

Look at the YAML code screenshot and running project screenshot:

Learning Docker: Dockerfiles, .dockerignore, and Port Mapping 🐳

Dharamraj Yadav — Sat, 07 Mar 2026 10:56:14 +0000

Hey everyone! Here’s a quick update on what I learned last week. I finally got hands-on with two essential Docker files: the Dockerfile and .dockerignore.

First up, let's talk about the .dockerignore file. If you've used Git, this works exactly like .gitignore. When we build an image, this file prevents Docker from copying over unnecessary files and folders, which helps keep our final image clean and lightweight.
Here is my setup:

Next, I created the Dockerfile. This is basically the instruction manual for your project. We write down all the necessary commands in here, and Docker uses this file as the blueprint to build our custom image.
Take a look at the code:

After building the image, it was time to run it. This is where I learned how port mapping works. Port mapping is simply telling the Docker container, "Hey, forward your internal project port to this specific port on my local system."

In my setup below, I mapped the ports so my project runs on port 5173 inside the container's terminal, but I can actually access it in my local browser using port 3200.
Check out the terminal and browser screenshots:

Getting Started with Docker: Images, Containers, Volumes, and Networks 🐳

Dharamraj Yadav — Tue, 24 Feb 2026 11:15:43 +0000

Hello Everyone as part of my journey transitioning to DevSecOps, today i dove into Docker.

In simple terms Docker is a software platform that allows you to build, test and deploy your applications quickly. Today i learned about four core concept of Docker, and i want to share my understanding with you all.

1. Docker Images (The Blueprint)
An image is basically the blueprint for a container.We create this blueprint by writing some instructions inside a file called a Dockerfile. it contains everything your application needs to run - the code, runtime, libraries, and environment variables.

2. Docker Container (The Running App)
If an image is a blueprint, then a container is the actual building. A container is simply the running instance of a Docker Image. You can start, stop, or delete a container anytime without affecting the original image.

3. Docker Volume (Permanent Storage)
By default, data inside the container temporary. this is where a volume come in. Volumes provide permanent storage for your container's data by saving it directly to your hard drive.

Real World Example: Suppose we host a database(like mongoDB) inside a container, and we have 1,000 users registered. if we delete or restart the container, all the users data will be lost. To prevent this we use a volume to safety store that database information permanently on the host machine.

4. Docker Network (The Communication Bridge)
When we create and run multiple containers at the same time, they are completely isolated from each other by default for security.
However in real applications, they need to communicate. For example if i have a Node.js backend running in one container and a database in another container, they need to talk each other. We Use Docker Networks to create a secure connection between these isolated containers.

My Journey Continues
Understanding these four concepts completely changed how I look at deployments. No more "It work's on my machine".

Hello World: My Journey from MERN Stack to DevSecOps 🚀

Dharamraj Yadav — Sat, 21 Feb 2026 04:13:32 +0000

Hello everyone!

My name is Dharamraj Yadav, and this is my first post on this platform. I am currently working as a MERN Stack Developer, where I build web applications and craft APIs using Node.js. I have gained solid experience working across the MERN stack.

Recently, I’ve been observing my seniors handle server management, specifically focusing on reducing AWS infrastructure costs. Watching them work over the last three months really inspired me. I realized that with a bit of effort, I have the confidence to learn these new concepts myself.

So, I started using AI tools like Gemini to deeply understand how servers, deployments, and cloud infrastructure actually work.

Now, I have officially decided to start my #LearnInPublic journey—transitioning from a MERN Stack Developer to DevSecOps. ⚙️🛡️

Please connect with me to follow my journey, and stay tuned for more updates and learnings from the tech field!

DevSecOps #MERN #AWS #LearnInPublic #DevOpsJourney