Linux for DevOps (Beginners)

Linux for DevOps (Beginners)

1. Linux Fundamentals

1.1 What is Open Source?

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

• Source code is publicly accessible
• Community-driven development and contributions
• 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 everything from smartphones to supercomputers.

• Linux is technically a kernel, not a full OS
• Full OS = Linux Kemel + GNU tools + package manager + desktop environment
• Popular distributions (distros): Ubuntu, Fedora, Debian, CentOS, Arch Linux
• Used in servers, cloud, Android, loT, supercomputers

1.3 Linux vs UNIX

Linux =Free, open-source, kemel by Linus Torvalds (1991)

UNIX = Proprietary OS from Bell Labs (1969), not free

macos = UNIX-based (BSD), proprietary by Apple

Similarity = Both follow POSIX standards; Linux was 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 run for years without reboots
• Lightweight- runs on old hardware
• Industry standard - most servers, cloud, and DevOps tools run on Linux
• Customizable - choose your own components and desktop

1.5 Linux vs Windows

Cost => Linux is free; Windows requires a license

Security => Linux is free; Windows requires a license

Usage => Linux dominates servers; Windows dominates desktops

CLI => Linux is CLI-first; Windows is GUI-first

File System = > Linux: ext4, XFS; Windows: NTFS, FAT32

Software => Linux uses package managers; Windows uses 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.

• Manages CPU, memory, and I/O devices
• Provides system calls for programs to request services
• Acts as a bridge between applications and hardware
• Linux kernel is monolithic - all kernel services run in kemel space

Installing Ubuntu via WSL (Windows Subsystem for Linux)

WSL lets you run a Linux terminal directly on Windows without a VM.

• Open PowerShell as Administrator
• Run: wsl -- install
• Restart your PC

Open Ubuntu from the Start Menu

 - Set username and password on first launch

Useful WSL commands:

ws1 -- list -- verbose

wsl -- set-default-version 2

# Open Linux files in Windows Explorer

# List installed distros

# Use WSL 2

explorer.exe .

3. Basic Terminal Commands

3.1 Navigation

pwd

Print Working Directory - shows current location

1s

List files and directories

1s -la

List all files (including hidden) with details

od <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

mkdir <name>

Create a new directory

mkdir -p a/b/c

Create nested directories

touch <file>

Create an 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 <arc> <dst>

Move or rename a file

cat <file>

Display file contents

less <file>

Scroll through file contents

nano <file>

Open file in nano text editor

vim <file>

Open file in vim text editor

3.3 File Permissions - chmod

Linux file permissions control who can read, write, or execute files.

Permission format: rwxrwxrwx (owner / group / others)

r=4

Read permission

w= 2

Write permission

x= 1

Execute permission

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

Links allow multiple references to the same file.

ln <src> <link>

Create a hard link - points to same inode

ln -s <src> <link>

Create a soft (symbolic) link - like a shortcut

alias 11='1s -la'

Create a command alias (session only)

Key difference: Deleting the original breaks a soft link but NOT a hard link.

4. File Handling & Text Processing

4.1 head & tail

head <file>

Show first 10 lines of a file

head -n 20 <file>

Show first 20 lines

tail <file>

Show last 10 lines

tail -f <file>

Follow file in real-time (great for logs)

4.2 wc -Word Count

we <file>

Show lines, words, and bytes

wc -1 <file>

Count lines only

wc -w <file>

Count words only

wc -c <file>

Count bytes/characters only

4.3 sort

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 the 2nd column

4.4 grep - Search Text

grep searches for patterns in files or output.

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 that do NOT match
grep -c 'pattern' file	Count matching lines
grep -E 'pllp2' file	Extended regex - match p1 OR p2

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

4.6 awk Text processing

awk '(print $1}'	Print first column of each line
file
awk '(print $1, $3)" file	Print columns 1 and 3
awk -F',' '(print $2}' file	Use comma as delimiter (CSV)
awk 'NR == 5' file awk '{sumt=$1)	Print line number 5 Sum all values in column 1
END(print sum]' f

5. Disk management $ archives

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

5.1 Zip/Unzip

zip archive.zip filel file2	Create a zip archive
zip -r archive.zip dir/	Zip an entire directory
unzip archive.zip	Extract a zip file
unzip -1 archive.zip	List contents without extracting

5.3 tar Tape Archive

tar -cvf archive.tar   creata a tea archive

tar -xvf archive.tar tar -czvf archive.tar.gz diz/	Extract a tar archive Create compressed tar.gz
tar -XzVf archive.tar.gz	Extract tar.gz
tar -tf archive.tar	List contents of tar file

6. Process management

6.1 View processes

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

6.2 Killing processes

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

6.3 Background Jobs & nohup

command &	Run command in background
jobs	List background jobs
fg 61 bg 41 Ctrl + Z nohup command & nohup command > out.log 2>61 &	Bring job 1 to foreground Resume job 1 in background Suspend current foreground job Run command immune to hangups (survives logout) Run nohup and save output to file
disown 41	Remove job from shell job table