Linux for DevOps (Beginners)

1. Linux Fundamentals

1.1 What is Open Source?

Open-source software has source code freely available for anyone to view, modify, and distribute. Linux is built on open-source principles.

Key Points	Description
Source code	Publicly accessible
Development	Community-driven
License	Free to use, modify, and redistribute
Examples	Linux, Python, Firefox, Android

1.2 What is Linux?

Linux is a free, open-source operating system kernel created by Linus Torvalds in 1991. It powers many devices from smartphones to supercomputers.

Aspect	Details
Kernel vs OS	Linux is a kernel, not a full OS
Full OS Components	Linux Kernel + GNU tools + package manager + desktop environment
Popular Distributions (Distros)	Ubuntu, Fedora, Debian, CentOS, Arch Linux
Usage	Servers, cloud, Android, IoT, supercomputers

1.3 Linux vs UNIX

System	Description	Notes
Linux	Free, open-source kernel by Linus Torvalds (1991)	Community-developed
UNIX	Proprietary OS from Bell Labs (1969)	Not free
macOS	UNIX-based (BSD), proprietary by Apple	UNIX-based, proprietary
Similarities	Both follow POSIX standards	Linux inspired by UNIX

1.4 Why Use Linux?

Free and open source — no licensing costs.
Highly secure — fewer viruses, strong permission model.
Stable and reliable — servers can run for years without reboot.
Lightweight — runs on old hardware.
Industry standard — most servers, cloud, and DevOps tools run on Linux.
Customizable — choose your own components and desktop environment.

1.5 Linux vs Windows

Feature	Linux	Windows
Cost	Free	Requires license
Security	Strong permissions, fewer viruses	More vulnerable, requires antivirus
Usage	Dominates servers	Dominates desktops
CLI vs GUI	CLI-first	GUI-first
File Systems	ext4, XFS	NTFS, FAT32
Software Install	Package managers (apt, yum)	Installers (.exe)

1.6 What is a Kernel?

The kernel is the core of the operating system. It manages hardware resources and allows software to communicate with hardware.

Functions	Description
Manages	CPU, memory, I/O devices
Provides	System calls for programs to request services
Acts as	Bridge between applications and hardware
Linux Kernel Type	Monolithic (all services run in kernel space)

2. Installing Ubuntu via WSL (Windows Subsystem for Linux)

WSL allows running a Linux terminal on Windows without a VM.

Steps	Commands/Actions
Open PowerShell as Administrator	Run: `wsl --install`
Restart PC	Restart your computer
Open Ubuntu	From Start Menu
Initial Setup	Set username and password on first launch

Useful WSL Commands

Command	Description
`wsl --list --verbose`	List installed distros with details
`wsl --set-default-version 2`	Set WSL version 2 as default
`explorer.exe .`	Open Linux files in Windows Explorer

3. Basic Terminal Commands

3.1 Navigation

Command	Description
`pwd`	Print working directory
`ls`	List files and directories
`ls -la`	List all files including hidden with details
`cd <dir>`	Change directory
`cd ..`	Go up one directory level
`cd ~`	Go to home directory
`cd /`	Go to root directory

3.2 File and Directory Operations

Command	Description
`mkdir <name>`	Create a new directory
`mkdir -p a/b/c`	Create nested directories
`touch <file>`	Create empty file or update timestamp
`rm <file>`	Remove a file
`rm -r <dir>`	Remove directory and contents recursively
`rm -zf <dir>`	Force remove without prompts (use carefully!)
`cp <src> <dst>`	Copy a file
`mv <src> <dst>`	Move or rename a file
`cat <file>`	Display file contents
`less <file>`	Scroll through file contents
`nano <file>`	Open file in nano editor
`vim <file>`	Open file in vim editor

3.3 File Permissions — `chmod`

Symbol	Value	Permission
r	4	Read
w	2	Write
x	1	Execute

Command	Effect
`chmod 755 file`	Owner: rwx, Group: r-x, Others: r-x
`chmod 644 file`	Owner: rw-, Group: r--, Others: r--
`chmod +x file`	Add execute permission for all
`chmod -w file`	Remove write permission

3.4 Links

Command	Description
`ln <src> <link>`	Create hard link (same inode)
`ln -s <src> <link>`	Create symbolic (soft) link
`alias ll='ls -la'`	Create command alias (session only)

Note: Deleting original breaks soft link but not hard link.

4. File Handling & Text Processing

4.1 head & tail

Command	Description
`head <file>`	Show first 10 lines
`head -n 20 <file>`	Show first 20 lines
`tail <file>`	Show last 10 lines
`tail -f <file>`	Follow file output live (logs)

4.2 wc — Word Count

Command	Description
`wc <file>`	Show lines, words, bytes
`wc -l <file>`	Count lines only
`wc -w <file>`	Count words only
`wc -c <file>`	Count bytes/characters only

4.3 sort

Command	Description
`sort <file>`	Sort lines alphabetically
`sort -r <file>`	Sort in reverse order
`sort -n <file>`	Sort numerically
`sort -u <file>`	Sort and remove duplicates
`sort -k2 <file>`	Sort by 2nd column

4.4 grep — Search Text

Command	Description
`grep 'pattern' file`	Search for pattern in file
`grep -i 'pattern' file`	Case-insensitive search
`grep -r 'pattern' dir/`	Recursive search in directory
`grep -n 'pattern' file`	Show line numbers with results
`grep -v 'pattern' file`	Show lines NOT matching pattern
`grep -c 'pattern' file`	Count matching lines
`grep -E 'p1	p2' file`

4.5 find — File Search

Command	Description
`find . -name '*.txt'`	Find all `.txt` files in current directory
`find / -name 'file.log'`	Find file across entire system
`find . -type d`	Find only directories
`find . -type f`	Find only regular files
`find . -mtime -7`	Find files modified in last 7 days
`find . -size +10M`	Find files larger than 10MB

4.6 awk — Text Processing

Command	Description
`awk '{print $1}' file`	Print first column
`awk '{print $1, $3}' file`	Print columns 1 and 3
`awk -F',' '{print $2}' file`	Use comma as delimiter (CSV)
`awk 'NR == 5' file`	Print line number 5
`awk '{sum+=$1} END {print sum}' file`	Sum all values in column 1

5. Disk Management & Archives

Command	Description
`df -h`	Show disk space usage (human-readable)
`du -sh <dir>`	Show size of directory
`du -h --max-depth=1`	Show sizes of subdirectories
`lsblk`	List block devices (disks, partitions)

5.1 Zip / Unzip

Command	Description
`zip archive.zip file1 file2`	Create a zip archive
`zip -r archive.zip dir/`	Zip an entire directory
`unzip archive.zip`	Extract zip archive
`unzip -l archive.zip`	List contents without extracting

5.2 tar — Tape Archive

Command	Description
`tar -cvf archive.tar dir/`	Create tar archive
`tar -xvf archive.tar`	Extract tar archive
`tar -czvf archive.tar.gz dir/`	Create compressed tar.gz archive
`tar -xzvf archive.tar.gz`	Extract tar.gz archive
`tar -tf archive.tar`	List contents of tar file

6. Process Management

6.1 View Processes

Command	Description
`ps`	List processes for current user
`ps aux`	List all processes with details
`ps aux	grep nginx`
`top`	Interactive real-time viewer
`htop`	Improved interactive process viewer
`pgrep <name>`	Find process ID by name

6.2 Killing Processes

Command	Description
`kill <PID>`	Send SIGTERM (graceful stop)
`kill -9 <PID>`	Send SIGKILL (force stop)
`killall <name>`	Kill all processes by name
`pkill <name>`	Kill process by pattern match

6.3 Background Jobs & nohup

Command	Description
`command &`	Run command in background
`jobs`	List background jobs
`fg %1`	Bring job 1 to foreground
`bg %1`	Resume job 1 in background
`Ctrl + Z`	Suspend current foreground job
`nohup command &`	Run command immune to hangups (survives logout)
`nohup command > out.log 2>&1 &`	Run nohup and save output to file
`disown %1`	Remove job from shell job table

7. Remote Access

7.1 SSH — Secure Shell

Command	Description
`ssh user@host`	Connect to remote server
`ssh user@192.168.1.10`	Connect via IP address
`ssh -p 2222 user@host`	Connect on custom port
`ssh-keygen`	Generate SSH key pair
`ssh-copy-id user@host`	Copy public key to remote server
`exit`	Disconnect SSH session

7.2 SCP — Secure Copy

Command	Description
`scp file.txt user@host:/path/`	Copy file TO remote server
`scp user@host:/path/file.txt .`	Copy file FROM remote server
`scp -r dir/ user@host:/path/`	Copy directory recursively
`scp -P 2222 file user@host:/path/`	Use custom SSH port

7.3 GUI Tools

PuTTY — SSH/Telnet client for Windows
WinSCP — GUI file transfer for Windows (SFTP/SCP)
FileZilla — Cross-platform FTP/SFTP client

8. Package Management

8.1 apt-get (Debian/Ubuntu)

Command	Description
`sudo apt-get update`	Update package list from repos
`sudo apt-get upgrade`	Upgrade all installed packages
`sudo apt-get install <pkg>`	Install a package
`sudo apt-get remove <pkg>`	Remove a package
`sudo apt-get autoremove`	Remove unused dependencies
`apt-cache search <keyword>`	Search for a package
`dpkg -l`	List all installed packages

8.2 wget — Download Files

Command	Description
`wget <URL>`	Download file from URL
`wget -O output.zip <URL>`	Download with custom filename
`wget -c <URL>`	Resume interrupted download
`wget -r <URL>`	Recursively download website

9. Scheduling & Automation

9.1 Cron Jobs

Cron is a time-based scheduler to run tasks automatically.

Command	Description
`crontab -e`	Edit cron jobs
`crontab -l`	List current cron jobs
`crontab -r`	Remove all cron jobs

Cron Syntax

* * * * * command
- - - - -
| | | | |
| | | | +---- Day of week (0-7, 0=Sun)
| | | +------ Month (1-12)
| | +-------- Day of month (1-31)
| +---------- Hour (0-23)
+------------ Minute (0-59)

Examples

Schedule	Command	Description
`0 2 * * * /backup.sh`	Run backup daily at 2 AM
`/5 * * * /check.sh`	Run every 5 minutes
`0 9 * * 1 /report.sh`	Run every Monday at 9 AM
`@reboot /startup.sh`	Run at system startup

9.2 Apache Airflow (Overview)

Platform for authoring, scheduling, monitoring workflows.
Uses Python DAGs (Directed Acyclic Graphs).
Better suited than cron for complex, dependent tasks.
Provides web UI for monitoring.
Supports retries, alerts, and dependency management.

10. Shell Scripting

10.1 Getting Started

#!/bin/bash
echo 'Hello World'
chmod +x script.sh
./script.sh

#!/bin/bash — Shebang line specifying interpreter.
echo — Print to terminal.
chmod +x — Make script executable.
./script.sh — Run script.

10.2 Variables

name='Alice'
echo $name
echo ${name}
read -p "Enter name: " name

Assign variable (no spaces around =).
Access variable with $.
Safer with ${}.
Read input from user.

10.3 Conditionals

if [ $age -gt 18 ]; then
  echo 'Adult'
elif [ $age -eq 18 ]; then
  echo 'Just 18'
else
  echo 'Minor'
fi

Operator	Description
`-eq`	Equal
`-ne`	Not equal
`-gt`	Greater than
`-lt`	Less than
`-ge`	Greater than or equal
`-le`	Less than or equal
`-z`	String is empty
`-f file`	File exists and is regular
`-d dir`	Directory exists

10.4 Loops

for i in 1 2 3 4 5; do
  echo "Number $i"
done

10.5 Advanced Scripting Tips

Use set -e to exit on any error.
Use set -x for debug mode (prints commands).
Always quote variables "${var}" to handle spaces.
Use [[ ]] for advanced test features.
Trap signals for cleanup: trap 'cleanup' EXIT.

11. Quick Reference Cheat Sheet

Command Group	Commands / Description
Navigation Basics	`pwd`, `ls`, `cd`
File Operations	`mkdir`, `touch`, `rm`, `cp`, `mv`
View File Contents	`cat`, `less`, `head`, `tail`
Search & Text Processing	`grep`, `find`, `awk`, `sort`, `wc`
Permissions Management	`chmod`, `chown`
Links and Aliases	`ln -s`, `alias`
Process Management	`ps`, `top`, `kill`, `nohup`
Disk and Archives	`df`, `du`, `tar`, `zip`
Remote Access	`ssh`, `scp`
Package Management	`apt-get`, `wget`
Scheduling Tasks	`crontab -e`
Shell Scripting	`#!/bin/bash`, `chmod +x`

4/21/2026