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Ragib Hasan
Ragib Hasan Subscriber

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🐧 Linux for DevOps — Complete Learning & Interview Preparation

#devops #interview #linux #sre

Goal: āĻāĻ•āĻĻāĻŽ raw level āĻĨā§‡āĻ•ā§‡ Linux āĻļāĻŋāĻ–ā§‡ DevOps/SRE/Cloud/Kubernetes āĻ•āĻžāĻœā§‡āĻ° āĻœāĻ¨ā§āĻ¯ production-ready foundation āĻ¤ā§ˆāĻ°āĻŋ āĻ•āĻ°āĻžāĨ¤

📌 Table of Contents

  1. Linux āĻ•ā§€?
  2. Linux Architecture
  3. Linux Distribution
  4. Terminal & Shell
  5. Filesystem
  6. Essential Commands
  7. File & Directory Management
  8. File Permissions
  9. Users & Groups
  10. Ownership
  11. Processes
  12. Jobs & Signals
  13. System Monitoring
  14. Package Management
  15. Environment Variables
  16. Shell & Bash
  17. Pipes & Redirection
  18. grep, sed, awk
  19. Networking
  20. Ports & Sockets
  21. DNS
  22. SSH
  23. SCP & Rsync
  24. File Compression
  25. Disk & Storage
  26. Mounting
  27. /proc, /sys, /dev
  28. systemd & Services
  29. Logs & journald
  30. Cron & Scheduling
  31. Linux Security
  32. Firewall
  33. TLS/SSL Basics
  34. Web Server Basics
  35. Reverse Proxy
  36. Linux for Docker
  37. Linux for Kubernetes
  38. Performance Troubleshooting
  39. Production Troubleshooting
  40. Bash Automation
  41. DevOps Practical Tasks
  42. Interview Questions
  43. Scenario-Based Interview
  44. Hands-on Projects
  45. Final Checklist

1. Linux āĻ•ā§€?

Linux āĻāĻ•āĻŸāĻŋ open-source Unix-like operating system kernelāĨ¤

Linux system āĻ¸āĻžāĻ§āĻžāĻ°āĻŖāĻ¤:

User
  ↓
Shell
  ↓
System Calls
  ↓
Linux Kernel
  ↓
Hardware
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Linux āĻ•ā§‡āĻ¨ DevOps-āĻ āĻ—ā§āĻ°ā§āĻ¤ā§āĻŦāĻĒā§‚āĻ°ā§āĻŖ?

āĻŦā§‡āĻļāĻŋāĻ°āĻ­āĻžāĻ—:

  • Cloud server
  • Web server
  • Docker container
  • Kubernetes node
  • CI/CD runner
  • Database server
  • Monitoring server
  • Production infrastructure

Linux-āĻāĻ° āĻ‰āĻĒāĻ° āĻšāĻ˛ā§‡āĨ¤

āĻ¤āĻžāĻ‡ DevOps engineer-āĻāĻ° āĻœāĻ¨ā§āĻ¯ Linux āĻšāĻ˛ā§‹ foundational skillāĨ¤

2. Linux Architecture

Basic architecture:

+-------------------------+
|        Applications     |
+-------------------------+
|        Shell            |
+-------------------------+
|     System Libraries    |
+-------------------------+
|     Linux Kernel        |
+-------------------------+
|        Hardware         |
+-------------------------+
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Kernel

Kernel manage āĻ•āĻ°ā§‡:

  • CPU
  • Memory
  • Processes
  • Filesystem
  • Networking
  • Devices
  • Security

3. Linux Distribution

āĻœāĻ¨āĻĒā§āĻ°āĻŋā§Ÿ distributions:

Ubuntu
Debian
Fedora
RHEL
Rocky Linux
AlmaLinux
Arch Linux
Amazon Linux
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DevOps-āĻ āĻŦāĻŋāĻļā§‡āĻˇāĻ­āĻžāĻŦā§‡:

Ubuntu
Amazon Linux
RHEL-based systems
Debian
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āĻœāĻžāĻ¨āĻž usefulāĨ¤

4. Terminal & Shell

Terminal āĻšāĻ˛ā§‹ interface āĻ¯ā§‡āĻ–āĻžāĻ¨ā§‡ command āĻšāĻžāĻ˛āĻžāĻ¨ā§‹ āĻšā§ŸāĨ¤

Shell command interpret āĻ•āĻ°ā§‡āĨ¤

Popular shells:

bash
zsh
fish
sh
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DevOps-āĻāĻ° āĻœāĻ¨ā§āĻ¯ Bash āĻ…āĻŦāĻļā§āĻ¯āĻ‡ āĻļāĻŋāĻ–āĻ¤ā§‡ āĻšāĻŦā§‡āĨ¤

Check:

echo $SHELL
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Current shell:

ps -p $$
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5. Linux Filesystem

Linux filesystem tree:

/
├── bin
├── boot
├── dev
├── etc
├── home
├── lib
├── opt
├── proc
├── root
├── run
├── sbin
├── srv
├── sys
├── tmp
├── usr
└── var
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āĻ—ā§āĻ°ā§āĻ¤ā§āĻŦāĻĒā§‚āĻ°ā§āĻŖ directories

/

Root filesystemāĨ¤

/home

User filesāĨ¤

/home/ragib
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/etc

System configurationāĨ¤

Examples:

/etc/hosts
/etc/fstab
/etc/ssh/
/etc/systemd/
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/var

Frequently changing dataāĨ¤

Examples:

/var/log
/var/cache
/var/lib
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/tmp

Temporary filesāĨ¤

/usr

Applications, libraries, utilitiesāĨ¤

/opt

Optional/third-party applicationsāĨ¤

/dev

Device filesāĨ¤

/proc

Kernel/process informationāĨ¤

/sys

Kernel/device informationāĨ¤

6. Navigation Commands

Current directory:

pwd
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List:

ls
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Detailed:

ls -l
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Hidden:

ls -la
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Change directory:

cd /etc
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Home:

cd ~
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Previous directory:

cd -
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Parent:

cd ..
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7. File Management

Create file:

touch app.log
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Create directory:

mkdir project
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Nested directories:

mkdir -p project/src/app
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Copy:

cp file.txt backup.txt
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Copy directory:

cp -r project backup/
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Move:

mv file.txt /tmp/
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Rename:

mv old.txt new.txt
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Delete:

rm file.txt
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Delete directory:

rm -r directory/
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Force:

rm -rf directory/
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⚠ī¸ rm -rf production server-āĻ āĻ…āĻ¤ā§āĻ¯āĻ¨ā§āĻ¤ āĻ¸āĻ¤āĻ°ā§āĻ•āĻ¤āĻžāĻ° āĻ¸āĻžāĻĨā§‡ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻ•āĻ°āĻ¤ā§‡ āĻšāĻŦā§‡āĨ¤

8. Reading Files

Small file:

cat file.txt
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Large file:

less file.txt
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First lines:

head file.txt
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Last lines:

tail file.txt
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Last 100:

tail -n 100 app.log
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Follow log:

tail -f app.log
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9. Searching Files

Find:

find /var/log -name "*.log"
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Search by type:

find . -type f
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Search directory:

find . -type d
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Search recently modified:

find . -mtime -1
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10. grep

Text search:

grep "error" app.log
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Case insensitive:

grep -i "error" app.log
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Recursive:

grep -r "database" /etc/
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Line number:

grep -n "error" app.log
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Invert match:

grep -v "INFO" app.log
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Multiple patterns:

grep -E "error|failed|critical" app.log
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11. Pipes

Pipe āĻāĻ•āĻŸāĻŋ command-āĻāĻ° output āĻ…āĻ¨ā§āĻ¯ command-āĻāĻ° input āĻšāĻŋāĻ¸ā§‡āĻŦā§‡ āĻĻā§‡ā§ŸāĨ¤

ps aux | grep nginx
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Example:

cat app.log | grep ERROR
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Better:

grep ERROR app.log
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Multiple:

ps aux | grep python | grep -v grep
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12. Redirection

Output file:

ls > files.txt
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Append:

ls >> files.txt
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Error redirect:

command 2> error.log
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Both stdout + stderr:

command > output.log 2>&1
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Modern Bash:

command &> output.log
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13. Permissions

Linux permission:

r = read
w = write
x = execute
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Example:

-rwxr-xr--
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Breakdown:

Owner      Group      Others
rwx        r-x        r--
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Numeric permissions:

r = 4
w = 2
x = 1
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Examples:

7 = rwx
6 = rw-
5 = r-x
4 = r--
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Therefore:

chmod 755 script.sh
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Means:

Owner:  rwx
Group:  r-x
Others: r-x
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14. chmod

Add execute:

chmod +x script.sh
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Remove write:

chmod -w file.txt
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Recursive:

chmod -R 755 directory/
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Symbolic:

chmod u+x script.sh
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15. chown

Change owner:

sudo chown user file.txt
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Owner + group:

sudo chown user:group file.txt
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Recursive:

sudo chown -R user:group directory/
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16. Users

Current user:

whoami
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User ID:

id
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Logged-in users:

who
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User information:

/etc/passwd
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Password information:

/etc/shadow
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/etc/shadow sensitive; normally readable only by privileged users.

17. Groups

Current groups:

groups
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Add user:

sudo useradd -m devops
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Set password:

sudo passwd devops
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Add to group:

sudo usermod -aG docker devops
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List groups:

getent group
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18. sudo

sudo allows authorized users to execute commands with elevated privileges.

Example:

sudo systemctl restart nginx
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Configuration:

/etc/sudoers
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Edit safely:

sudo visudo
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19. Processes

List processes:

ps
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All processes:

ps aux
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Tree:

pstree
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Interactive:

top
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Better interactive monitor:

htop
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20. Process IDs

Every process has PID.

ps aux
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Find process:

pgrep nginx
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Process details:

ps -p 1234
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21. kill

Terminate:

kill 1234
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Force:

kill -9 1234
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Important signals:

SIGTERM = 15
SIGKILL = 9
SIGHUP  = 1
SIGINT  = 2
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Prefer:

kill PID
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before:

kill -9 PID
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because SIGTERM allows graceful shutdownāĨ¤

22. Background Processes

Run background:

command &
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Jobs:

jobs
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Bring foreground:

fg
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Background:

bg
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Detach process:

nohup command &
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23. System Monitoring

CPU:

top
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Memory:

free -h
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Disk:

df -h
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Directory size:

du -sh directory/
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Load average:

uptime
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System information:

uname -a
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CPU:

lscpu
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Memory:

free -h
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24. Load Average

Check:

uptime
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Example:

load average: 1.20, 0.80, 0.50
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āĻāĻ—ā§āĻ˛ā§‹ āĻ¸āĻžāĻ§āĻžāĻ°āĻŖāĻ¤:

1 minute
5 minutes
15 minutes
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load averageāĨ¤

Interview-āĻ āĻŽāĻ¨ā§‡ āĻ°āĻžāĻ–āĻŦā§‡:

Load average āĻļā§āĻ§ā§ CPU utilization āĻ¨ā§Ÿ; runnable āĻāĻŦāĻ‚ āĻ•āĻŋāĻ›ā§ āĻ•ā§āĻˇā§‡āĻ¤ā§āĻ°ā§‡ uninterruptible tasks-āĻāĻ° āĻšāĻžāĻĒāĻ“ reflect āĻ•āĻ°āĻ¤ā§‡ āĻĒāĻžāĻ°ā§‡āĨ¤

25. Package Management

Ubuntu/Debian:

sudo apt update
sudo apt install nginx
sudo apt remove nginx
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RHEL/Fedora:

dnf install nginx
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Arch:

sudo pacman -S nginx
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Package query:

pacman -Qs nginx
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DevOps engineer-āĻāĻ° āĻœāĻ¨ā§āĻ¯ distribution āĻ…āĻ¨ā§āĻ¯āĻžā§Ÿā§€ package manager āĻœāĻžāĻ¨āĻž usefulāĨ¤

26. Environment Variables

Show:

env
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Specific:

echo $PATH
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Set:

export APP_ENV=production
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Check:

echo $APP_ENV
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Permanent shell variable āĻ¸āĻžāĻ§āĻžāĻ°āĻŖāĻ¤:

~/.bashrc
~/.zshrc
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server/application configuration-āĻāĻ° āĻ•ā§āĻˇā§‡āĻ¤ā§āĻ°ā§‡ environment variables āĻ–ā§āĻŦ āĻ—ā§āĻ°ā§āĻ¤ā§āĻŦāĻĒā§‚āĻ°ā§āĻŖāĨ¤

27. PATH

Check:

echo $PATH
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āĻ•ā§‹āĻ¨ executable āĻ•ā§‹āĻĨāĻžā§Ÿ:

which python
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āĻ†āĻ°āĻ“ reliable:

command -v python
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PATH-āĻāĻ° āĻĒā§āĻ°āĻ¤āĻŋāĻŸāĻŋ directory:

echo $PATH | tr ':' '\n'
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28. Bash Scripting

Basic:

#!/bin/bash

echo "Hello DevOps"
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Variable:

NAME="DevOps"

echo "$NAME"
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Condition:

if [ -f app.log ]; then
    echo "File exists"
fi
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Loop:

for file in *.log; do
    echo "$file"
done
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Function:

backup() {
    echo "Running backup"
}
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29. Exit Codes

āĻļā§‡āĻˇ command-āĻāĻ° exit code:

echo $?
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Generally:

0 = success
non-zero = failure
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Script:

command

if [ $? -ne 0 ]; then
    echo "Command failed"
fi
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Better:

if ! command; then
    echo "Failed"
fi
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Production scripts:

set -euo pipefail
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āĻāĻ° meaning āĻŦā§āĻāĻ¤ā§‡ āĻšāĻŦā§‡āĨ¤

30. awk

Column processing:

awk '{print $1}' file.txt
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Example:

ps aux | awk '{print $1, $2}'
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Useful for:

  • logs
  • metrics
  • CSV-like text
  • command output

31. sed

Text replacement:

sed 's/old/new/g' file.txt
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Delete line:

sed '3d' file.txt
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Configuration automation-āĻ sed frequently āĻĻā§‡āĻ–āĻž āĻ¯āĻžā§ŸāĨ¤

32. cut 

echo "devops:linux:docker" | cut -d ':' -f 1
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Output:

devops
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33. sort 

sort file.txt
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Reverse:

sort -r file.txt
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Numeric:

sort -n numbers.txt
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34. uniq 

sort file.txt | uniq
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Count:

sort file.txt | uniq -c
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35. Networking Fundamentals

DevOps-āĻāĻ° āĻœāĻ¨ā§āĻ¯ networking āĻ…āĻŦāĻļā§āĻ¯āĻ‡ āĻœāĻžāĻ¨āĻ¤ā§‡ āĻšāĻŦā§‡āĨ¤

āĻļāĻŋāĻ–āĻ¤ā§‡ āĻšāĻŦā§‡:

IP
MAC
TCP
UDP
HTTP
HTTPS
DNS
DHCP
NAT
Routing
Ports
Sockets
Firewall
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36. IP Address

IPv4 example:

192.168.1.10
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Private ranges:

10.0.0.0/8

172.16.0.0/12

192.168.0.0/16
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Interface:

ip addr
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Short:

ip a
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37. Routing

Routes:

ip route
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Default route:

default via 192.168.1.1
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Important interview concept:

Default gateway āĻšāĻ˛ā§‹ āĻāĻŽāĻ¨ router āĻ¯ā§‡āĻ–āĻžāĻ¨ā§‡ system unknown destinations-āĻāĻ° traffic āĻĒāĻžāĻ āĻžā§ŸāĨ¤

38. Connectivity

Ping:

ping google.com
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Trace:

traceroute google.com
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āĻŦāĻž:

tracepath google.com
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39. Ports

Listening ports:

ss -tulpn
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Specific port:

ss -lntp | grep :8000
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Common ports:

22   SSH
53   DNS
80   HTTP
443  HTTPS
3306 MySQL
5432 PostgreSQL
6379 Redis
8000 FastAPI
8080 Common HTTP alternative
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40. DNS

DNS domain → IP resolve āĻ•āĻ°ā§‡āĨ¤

Check:

dig google.com
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āĻŦāĻž:

nslookup google.com
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Simple:

getent hosts google.com
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DNS configuration:

/etc/resolv.conf
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Hosts:

/etc/hosts
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41. curl

HTTP request:

curl https://example.com
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Headers:

curl -I https://example.com
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POST:

curl -X POST \
  -H "Content-Type: application/json" \
  -d '{"name":"Ragib"}' \
  http://localhost:8000/predict
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DevOps troubleshooting-āĻāĻ° āĻœāĻ¨ā§āĻ¯ curl āĻ…āĻ¤ā§āĻ¯āĻ¨ā§āĻ¤ āĻ—ā§āĻ°ā§āĻ¤ā§āĻŦāĻĒā§‚āĻ°ā§āĻŖāĨ¤

42. wget

Download:

wget https://example.com/file.zip
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43. SSH

Remote server access:

ssh user@server-ip
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Specific key:

ssh -i key.pem user@server-ip
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SSH config:

~/.ssh/config
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44. SSH Keys

Generate:

ssh-keygen -t ed25519
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Public key:

~/.ssh/id_ed25519.pub
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Private key:

~/.ssh/id_ed25519
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Private key āĻ•āĻ–āĻ¨ā§‹ share āĻŦāĻž Git repository-āĻ¤ā§‡ commit āĻ•āĻ°āĻž āĻ¯āĻžāĻŦā§‡ āĻ¨āĻžāĨ¤

45. SCP

Copy local → remote:

scp file.txt user@server:/tmp/
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Remote → local:

scp user@server:/tmp/file.txt .
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46. rsync

Efficient synchronization:

rsync -av project/ server:/backup/project/
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Delete destination extras:

rsync -av --delete source/ destination/
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Production backup/deployment workflows-āĻ usefulāĨ¤

47. Compression

tar:

tar -cvf archive.tar directory/
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Extract:

tar -xvf archive.tar
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gzip:

tar -czvf archive.tar.gz directory/
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Extract:

tar -xzvf archive.tar.gz
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48. Disk Management

Disk usage:

df -h
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Directory:

du -sh /var/*
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Block devices:

lsblk
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Partitions:

sudo fdisk -l
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49. Mount

Mount filesystem:

sudo mount /dev/sdb1 /mnt
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Unmount:

sudo umount /mnt
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Persistent mounts:

/etc/fstab
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50. Inodes

Filesystem āĻļā§āĻ§ā§ file size āĻĻāĻŋā§Ÿā§‡ manage āĻ•āĻ°ā§‡ āĻ¨āĻž; inode-āĻ“ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻ•āĻ°ā§‡āĨ¤

Check:

df -i
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Possible problem:

Disk space available
BUT
Inodes exhausted
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āĻ¤āĻ–āĻ¨ āĻ¨āĻ¤ā§āĻ¨ file āĻ¤ā§ˆāĻ°āĻŋ āĻ•āĻ°āĻ¤ā§‡ āĻ¸āĻŽāĻ¸ā§āĻ¯āĻž āĻšāĻ¤ā§‡ āĻĒāĻžāĻ°ā§‡āĨ¤

51. /proc

/proc virtual filesystemāĨ¤

Process:

/proc/<PID>/
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CPU:

/proc/cpuinfo
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Memory:

/proc/meminfo
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Uptime:

/proc/uptime
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52. /dev

Device filesāĨ¤

Examples:

/dev/sda
/dev/nvme0n1
/dev/null
/dev/zero
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/dev/null:

command > /dev/null
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53. /dev/null

Anything written āĻāĻ–āĻžāĻ¨ā§‡ discard āĻšā§ŸāĨ¤

echo "hello" > /dev/null
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Suppress output:

command > /dev/null 2>&1
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54. systemd

Modern Linux systems-āĻ systemd service manager āĻšāĻŋāĻ¸ā§‡āĻŦā§‡ āĻŦā§āĻ¯āĻŦāĻšā§ƒāĻ¤ āĻšā§ŸāĨ¤

Service status:

systemctl status nginx
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Start:

sudo systemctl start nginx
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Stop:

sudo systemctl stop nginx
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Restart:

sudo systemctl restart nginx
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Enable on boot:

sudo systemctl enable nginx
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Disable:

sudo systemctl disable nginx
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55. systemd Logs 

journalctl
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Specific service:

journalctl -u nginx
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Follow:

journalctl -u nginx -f
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Recent:

journalctl --since "1 hour ago"
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Boot logs:

journalctl -b
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56. Linux Logs

Common location:

/var/log/
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Examples:

/var/log/syslog
/var/log/auth.log
/var/log/nginx/
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Distribution āĻ…āĻ¨ā§āĻ¯āĻžā§Ÿā§€ filenames āĻ­āĻŋāĻ¨ā§āĻ¨ āĻšāĻ¤ā§‡ āĻĒāĻžāĻ°ā§‡āĨ¤

57. Log Rotation

Long-running production systems-āĻ logs unlimited growth āĻ•āĻ°āĻ˛ā§‡ disk full āĻšāĻ¤ā§‡ āĻĒāĻžāĻ°ā§‡āĨ¤

Concepts:

logrotate
rotation
compression
retention
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Configuration:

/etc/logrotate.conf
/etc/logrotate.d/
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58. Cron

Scheduled jobsāĨ¤

Edit:

crontab -e
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Format:

minute hour day month weekday command
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Example:

0 2 * * * /home/user/backup.sh
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āĻŽāĻžāĻ¨ā§‡ āĻĒā§āĻ°āĻ¤āĻŋāĻĻāĻŋāĻ¨ āĻ°āĻžāĻ¤ ā§¨āĻŸāĻžā§ŸāĨ¤

59. Linux Security

Must know:

Users
Groups
Permissions
sudo
SSH
Firewall
SELinux/AppArmor
Secrets
Updates
Least privilege
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60. Firewall

Common tools:

ufw
firewalld
nftables
iptables
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Ubuntu example:

sudo ufw status
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Allow SSH:

sudo ufw allow 22
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Allow HTTP:

sudo ufw allow 80
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61. SELinux / AppArmor

Linux security frameworksāĨ¤

Know the concepts:

Mandatory Access Control
Policies
Security Context
Least Privilege
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RHEL ecosystem-āĻ SELinux āĻ—ā§āĻ°ā§āĻ¤ā§āĻŦāĻĒā§‚āĻ°ā§āĻŖāĨ¤

Ubuntu-āĻ¤ā§‡ AppArmor commonly āĻĻā§‡āĻ–āĻž āĻ¯āĻžā§ŸāĨ¤

62. Web Server Basics

Popular:

Nginx
Apache
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Nginx can act as:

Web Server
Reverse Proxy
Load Balancer
TLS Termination
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63. Reverse Proxy

Architecture:

Client
  ↓
Nginx
  ↓
FastAPI
  ↓
ML Model
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Nginx backend-āĻāĻ° āĻ¸āĻžāĻŽāĻ¨ā§‡ āĻĨāĻžāĻ•ā§‡āĨ¤

Benefits:

  • TLS termination
  • routing
  • load balancing
  • buffering
  • security controls

64. Linux + Docker

Docker Linux-āĻāĻ° āĻ¨āĻŋāĻšā§‡āĻ° āĻ…āĻ¨ā§‡āĻ• core concept āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻ•āĻ°ā§‡:

Namespaces
cgroups
filesystem layers
networking
process isolation
capabilities
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āĻ¤āĻžāĻ‡ Docker āĻļā§‡āĻ–āĻžāĻ° āĻ†āĻ—ā§‡ Linux fundamentals āĻļāĻ•ā§āĻ¤ āĻšāĻ“ā§ŸāĻž āĻ–ā§āĻŦ usefulāĨ¤

65. Docker-āĻāĻ° āĻœāĻ¨ā§āĻ¯ Linux Knowledge

āĻŦāĻŋāĻļā§‡āĻˇāĻ­āĻžāĻŦā§‡ āĻœāĻžāĻ¨āĻ¤ā§‡ āĻšāĻŦā§‡:

  • Process
  • PID
  • Namespace
  • cgroups
  • Filesystem
  • permissions
  • networking
  • ports
  • mounts
  • signals

Container-āĻāĻ° āĻ­āĻŋāĻ¤āĻ°ā§‡āĻ° process āĻ¸āĻžāĻ§āĻžāĻ°āĻŖāĻ¤ host-āĻāĻ° kernel āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻ•āĻ°ā§‡āĨ¤

66. Linux + Kubernetes

Kubernetes node troubleshooting-āĻāĻ° āĻœāĻ¨ā§āĻ¯:

ps
top
free
df
du
ss
ip
journalctl
systemctl
curl
grep
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āĻ–ā§āĻŦ āĻ­āĻžāĻ˛ā§‹āĻ­āĻžāĻŦā§‡ āĻœāĻžāĻ¨āĻ¤ā§‡ āĻšāĻŦā§‡āĨ¤

67. Kubernetes Troubleshooting Example

Pod:

CrashLoopBackOff
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āĻ¤āĻ–āĻ¨:

kubectl logs pod-name
kubectl describe pod pod-name
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āĻ•āĻŋāĻ¨ā§āĻ¤ā§ underlying node problem āĻšāĻ˛ā§‡ Linux:

journalctl
df -h
free -h
top
systemctl
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āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻ•āĻ°āĻ¤ā§‡ āĻšāĻŦā§‡āĨ¤

68. CPU Troubleshooting

Problem:

CPU = 100%
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Check:

top
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āĻŦāĻž:

htop
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Process:

ps aux --sort=-%cpu | head
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āĻ¤āĻžāĻ°āĻĒāĻ° determine āĻ•āĻ°āĻ¤ā§‡ āĻšāĻŦā§‡:

Which process?
Why?
Application issue?
Infinite loop?
Too much traffic?
CPU throttling?
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69. Memory Troubleshooting

Check:

free -h
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Processes:

ps aux --sort=-%mem | head
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OOM-related logs:

dmesg | grep -i oom
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āĻŦāĻž:

journalctl | grep -i oom
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70. Disk Full Troubleshooting

āĻĒā§āĻ°āĻĨāĻŽ:

df -h
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āĻ¤āĻžāĻ°āĻĒāĻ°:

du -sh /*
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Specific:

du -sh /var/*
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Large files:

find /var -type f -size +1G
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Check inode:

df -i
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Potential causes:

Huge logs
Docker images
Docker volumes
Deleted-but-open files
Temporary files
Backups
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71. Deleted File Still Using Disk

āĻāĻ•āĻŸāĻŋ process file delete āĻ•āĻ°āĻžāĻ° āĻĒāĻ°ā§‡āĻ“ file descriptor open āĻ°āĻžāĻ–āĻ¤ā§‡ āĻĒāĻžāĻ°ā§‡āĨ¤

Check:

lsof +L1
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āĻāĻŸāĻž production troubleshooting interview-āĻ useful scenarioāĨ¤

72. Port Already in Use

Error:

Address already in use
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Check:

ss -lntp | grep :8000
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āĻŦāĻž:

lsof -i :8000
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Process identify āĻ•āĻ°ā§‡ graceful stop āĻ•āĻ°āĻ¤ā§‡ āĻšāĻŦā§‡āĨ¤

73. Service Not Starting

āĻ§āĻžāĻĒ:

systemctl status service
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āĻ¤āĻžāĻ°āĻĒāĻ°:

journalctl -u service
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āĻ¤āĻžāĻ°āĻĒāĻ°:

systemctl cat service
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āĻ¤āĻžāĻ°āĻĒāĻ° configuration validateāĨ¤

74. Server Reachable āĻ•āĻŋāĻ¨ā§āĻ¤ā§ Website āĻ•āĻžāĻœ āĻ•āĻ°āĻ›ā§‡ āĻ¨āĻž

Layer-by-layer troubleshoot:

1. DNS
2. Network
3. Port
4. Firewall
5. Web server
6. Reverse proxy
7. Application
8. Database
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Commands:

dig domain.com
ping server
ss -lntp
curl localhost
curl backend:8000
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75. HTTP Status Codes

Must know:

200 OK
201 Created
204 No Content

301/302 Redirect

400 Bad Request
401 Unauthorized
403 Forbidden
404 Not Found
405 Method Not Allowed
408 Request Timeout
409 Conflict
429 Too Many Requests

500 Internal Server Error
502 Bad Gateway
503 Service Unavailable
504 Gateway Timeout
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76. 502 vs 503 vs 504

502 Bad Gateway

Proxy backend āĻĨā§‡āĻ•ā§‡ valid response āĻĒāĻžā§ŸāĻ¨āĻŋāĨ¤

503 Service Unavailable

Service available āĻ¨ā§Ÿ āĻŦāĻž overloaded āĻšāĻ¤ā§‡ āĻĒāĻžāĻ°ā§‡āĨ¤

504 Gateway Timeout

Upstream response āĻĻāĻŋāĻ¤ā§‡ āĻŦā§‡āĻļāĻŋ āĻ¸āĻŽā§Ÿ āĻ¨āĻŋā§Ÿā§‡āĻ›ā§‡āĨ¤

DevOps interview-āĻ āĻāĻ—ā§āĻ˛ā§‹āĻ° āĻĒāĻžāĻ°ā§āĻĨāĻ•ā§āĻ¯ āĻœāĻžāĻ¨āĻž āĻ—ā§āĻ°ā§āĻ¤ā§āĻŦāĻĒā§‚āĻ°ā§āĻŖāĨ¤

77. TCP vs UDP

TCP

  • Connection-oriented
  • Reliable
  • Ordered
  • Retransmission

UDP

  • Connectionless
  • Lower overhead
  • No guaranteed delivery
  • Faster for suitable workloads

Examples:

TCP → HTTP/HTTPS, SSH
UDP → DNS queries commonly, streaming/real-time workloads
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78. TCP Connection States

Know:

LISTEN
SYN-SENT
SYN-RECEIVED
ESTABLISHED
FIN-WAIT
TIME-WAIT
CLOSE-WAIT
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Check:

ss -tan
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79. TIME_WAIT

Connection close āĻšāĻ“ā§ŸāĻžāĻ° āĻĒāĻ° TCP āĻ•āĻŋāĻ›ā§ āĻ¸āĻŽā§Ÿ state āĻ§āĻ°ā§‡ āĻ°āĻžāĻ–ā§‡ āĻ¯āĻžāĻ¤ā§‡ delayed packets āĻ¸āĻŽāĻ¸ā§āĻ¯āĻž āĻ¨āĻž āĻ•āĻ°ā§‡āĨ¤

High traffic systems-āĻ āĻ…āĻ¨ā§‡āĻ• TIME_WAIT āĻĻā§‡āĻ–āĻž āĻ¯ā§‡āĻ¤ā§‡ āĻĒāĻžāĻ°ā§‡āĨ¤

Interview-āĻ āĻļā§āĻ§ā§ “TIME_WAIT is bad” āĻŦāĻ˛āĻž āĻ­ā§āĻ˛āĨ¤

80. File Descriptors

Linux-āĻ process files, sockets āĻ‡āĻ¤ā§āĻ¯āĻžāĻĻāĻŋ file descriptors āĻšāĻŋāĻ¸ā§‡āĻŦā§‡ handle āĻ•āĻ°ā§‡āĨ¤

Check limits:

ulimit -n
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Process open files:

lsof -p PID
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81. Hard Link vs Soft Link

Soft link:

ln -s original.txt link.txt
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Hard link:

ln original.txt hardlink.txt
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Soft link

  • āĻ†āĻ˛āĻžāĻĻāĻž inode
  • target-āĻāĻ° path reference āĻ•āĻ°ā§‡
  • target delete āĻšāĻ˛ā§‡ broken āĻšāĻ¤ā§‡ āĻĒāĻžāĻ°ā§‡

Hard link

  • āĻāĻ•āĻ‡ inode
  • āĻāĻ•āĻ‡ filesystem-āĻāĻ° āĻŽāĻ§ā§āĻ¯ā§‡ āĻ¸āĻžāĻ§āĻžāĻ°āĻŖāĻ¤
  • original filename delete āĻšāĻ˛ā§‡āĻ“ data āĻĨāĻžāĻ•āĻ¤ā§‡ āĻĒāĻžāĻ°ā§‡

82. Symbolic Links in DevOps

Common examples:

/etc/nginx/sites-enabled/
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Configuration management āĻāĻŦāĻ‚ system files-āĻ symbolic links āĻĻā§‡āĻ–āĻ¤ā§‡ āĻĒāĻžāĻŦā§‡āĨ¤

83. Process vs Thread

Process

Independent execution contextāĨ¤

Thread

āĻāĻ•āĻ‡ process-āĻāĻ° āĻŽāĻ§ā§āĻ¯ā§‡ execution unitāĨ¤

Threads āĻ¸āĻžāĻ§āĻžāĻ°āĻŖāĻ¤ āĻāĻ•āĻ‡ process-āĻāĻ° memory share āĻ•āĻ°ā§‡āĨ¤

84. Zombie Process

Parent process child-āĻāĻ° exit status collect āĻ¨āĻž āĻ•āĻ°āĻ˛ā§‡ zombie process āĻšāĻ¤ā§‡ āĻĒāĻžāĻ°ā§‡āĨ¤

Check:

ps aux | grep Z
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Zombie kill āĻ•āĻ°āĻžāĻ° āĻŦāĻĻāĻ˛ā§‡ āĻ¸āĻžāĻ§āĻžāĻ°āĻŖāĻ¤ parent process-āĻāĻ° issue investigate āĻ•āĻ°āĻ¤ā§‡ āĻšā§ŸāĨ¤

85. Orphan Process

Parent process terminate āĻšāĻ˛ā§‡ child orphan āĻšāĻ¤ā§‡ āĻĒāĻžāĻ°ā§‡ āĻāĻŦāĻ‚ system-āĻāĻ° init/systemd process āĻ¤āĻžāĻ•ā§‡ adopt āĻ•āĻ°āĻ¤ā§‡ āĻĒāĻžāĻ°ā§‡āĨ¤

86. Context Switching

CPU āĻāĻ• execution context āĻĨā§‡āĻ•ā§‡ āĻ…āĻ¨ā§āĻ¯āĻŸāĻŋāĻ¤ā§‡ switch āĻ•āĻ°ā§‡āĨ¤

Too many processes/threads context-switch overhead āĻ¤ā§ˆāĻ°āĻŋ āĻ•āĻ°āĻ¤ā§‡ āĻĒāĻžāĻ°ā§‡āĨ¤

Tools:

vmstat
pidstat
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87. vmstat 

vmstat 1
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Useful for:

CPU
memory
swap
processes
I/O
context switching
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88. iostat

Disk I/O troubleshooting:

iostat
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Useful metrics:

IOPS
throughput
utilization
latency
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89. sar

Historical/current system performance statistics-āĻāĻ° āĻœāĻ¨ā§āĻ¯ usefulāĨ¤

sar
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CPU:

sar -u
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Memory:

sar -r
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Network:

sar -n DEV
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90. Network Troubleshooting Toolkit

Must know:

ip
ss
ping
traceroute
tracepath
dig
nslookup
curl
wget
nc
tcpdump
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91. netcat

Port testing:

nc -zv server 8000
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Useful for checking TCP connectivityāĨ¤

92. tcpdump

Packet capture:

sudo tcpdump -i any port 8000
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HTTP traffic investigation:

sudo tcpdump -i any host 10.0.0.5
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Advanced networking troubleshooting-āĻāĻ° āĻœāĻ¨ā§āĻ¯ āĻ—ā§āĻ°ā§āĻ¤ā§āĻŦāĻĒā§‚āĻ°ā§āĻŖāĨ¤

93. Linux Security Checklist

Production server:

[ ] Disable unnecessary services
[ ] Use SSH keys
[ ] Avoid root login
[ ] Use least privilege
[ ] Keep packages updated
[ ] Configure firewall
[ ] Protect secrets
[ ] Monitor logs
[ ] Rotate credentials
[ ] Backup critical data
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94. DevOps-āĻ Linux-āĻāĻ° āĻ¸āĻŦāĻšā§‡ā§Ÿā§‡ āĻ—ā§āĻ°ā§āĻ¤ā§āĻŦāĻĒā§‚āĻ°ā§āĻŖ Commands

āĻāĻ‡ commandāĻ—ā§āĻ˛ā§‹ āĻŽā§āĻ–āĻ¸ā§āĻĨ āĻ¨āĻž āĻšāĻ˛ā§‡āĻ“ confidently āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻ•āĻ°āĻ¤ā§‡ āĻĒāĻžāĻ°āĻ¤ā§‡ āĻšāĻŦā§‡:

pwd
ls
cd
cp
mv
rm
mkdir
touch
cat
less
head
tail
grep
find
awk
sed
cut
sort
uniq
chmod
chown
sudo
ps
top
htop
kill
pkill
pgrep
free
df
du
lsblk
mount
ip
ss
ping
curl
wget
dig
nc
tcpdump
ssh
scp
rsync
tar
systemctl
journalctl
crontab
lsof
uname
uptime
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95. Production Troubleshooting Method

āĻ•āĻ–āĻ¨ā§‹ random command āĻšāĻžāĻ˛āĻžāĻ¨ā§‹ āĻ‰āĻšāĻŋāĻ¤ āĻ¨ā§ŸāĨ¤

āĻāĻ‡ framework follow āĻ•āĻ°āĻŦā§‡:

1. Identify the symptom
        ↓
2. Determine scope
        ↓
3. Check recent changes
        ↓
4. Check logs
        ↓
5. Check metrics
        ↓
6. Check resource usage
        ↓
7. Check network
        ↓
8. Reproduce if possible
        ↓
9. Fix
        ↓
10. Verify
        ↓
11. Document
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96. DevOps Incident Example

Problem

Application suddenly slowāĨ¤

Step 1

Check CPU:

top
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Step 2

Memory:

free -h
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Step 3

Disk:

df -h
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Step 4

Network:

ss -s
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Step 5

Application logs:

journalctl -u app
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Step 6

Recent deployment:

What changed?
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Step 7

Check upstream/database.

āĻāĻ­āĻžāĻŦā§‡ systematic troubleshooting āĻ•āĻ°āĻ¤ā§‡ āĻšāĻŦā§‡āĨ¤

97. Linux + ML Inference Platform

āĻ¤ā§‹āĻŽāĻžāĻ° ML inference project-āĻ Linux knowledge āĻ¸āĻ°āĻžāĻ¸āĻ°āĻŋ āĻ˛āĻžāĻ—āĻŦā§‡āĨ¤

Architecture:

Linux Server
    ↓
Docker
    ↓
Kubernetes
    ↓
FastAPI
    ↓
ML Model
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Troubleshooting:

High CPU
    ↓
top

High memory
    ↓
free / ps

Disk full
    ↓
df / du

Port issue
    ↓
ss

Service issue
    ↓
systemctl / journalctl

Network issue
    ↓
ip / ss / curl / dig

Container issue
    ↓
docker logs / docker stats
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98. Interview Preparation — Basic Questions

Q1. Linux āĻ•ā§€?

Linux āĻāĻ•āĻŸāĻŋ open-source Unix-like operating system kernel; Linux distributions kernel-āĻāĻ° āĻ¸āĻžāĻĨā§‡ user-space tools āĻ“ package ecosystem āĻĒā§āĻ°āĻĻāĻžāĻ¨ āĻ•āĻ°ā§‡āĨ¤

Q2. Kernel āĻ•ā§€?

Kernel hardware āĻāĻŦāĻ‚ applications-āĻāĻ° āĻŽāĻ§ā§āĻ¯ā§‡ āĻĒā§āĻ°āĻ§āĻžāĻ¨ interface āĻšāĻŋāĻ¸ā§‡āĻŦā§‡ āĻ•āĻžāĻœ āĻ•āĻ°ā§‡ āĻāĻŦāĻ‚ CPU, memory, processes, devices āĻ“ networking-āĻāĻ° āĻŽāĻ¤ā§‹ resources manage āĻ•āĻ°ā§‡āĨ¤

Q3. Linux-āĻ /etc āĻ•ā§€?

System configuration files-āĻāĻ° āĻĒā§āĻ°āĻ§āĻžāĻ¨ directoryāĨ¤

Q4. /var āĻ•ā§€?

Variable data āĻ¯ā§‡āĻŽāĻ¨ logs, caches āĻāĻŦāĻ‚ application state-āĻāĻ° āĻœāĻ¨ā§āĻ¯ āĻŦā§āĻ¯āĻŦāĻšā§ƒāĻ¤ āĻšā§ŸāĨ¤

Q5. Process āĻ•ā§€?

Running program-āĻāĻ° āĻāĻ•āĻŸāĻŋ execution instanceāĨ¤

Q6. PID āĻ•ā§€?

Process IdentifierāĨ¤

Q7. kill -9 āĻ•ā§€ āĻ•āĻ°ā§‡?

SIGKILL āĻĒāĻžāĻ āĻžā§ŸāĨ¤ Process graceful cleanup āĻ•āĻ°āĻžāĻ° āĻ¸ā§āĻ¯ā§‹āĻ— āĻĒāĻžā§Ÿ āĻ¨āĻžāĨ¤

Q8. chmod 755 āĻ•ā§€? 

Owner  = rwx
Group  = r-x
Other  = r-x
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Q9. chmod 644 āĻ•ā§€? 

Owner  = rw-
Group  = r--
Other  = r--
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Q10. sudo āĻ•ā§€?

Authorized user-āĻ•ā§‡ privileged command execute āĻ•āĻ°āĻžāĻ° āĻ¸ā§āĻ¯ā§‹āĻ— āĻĻā§‡ā§ŸāĨ¤

99. Intermediate Interview Questions

Q11. Hard link āĻāĻŦāĻ‚ soft link-āĻāĻ° difference?

Hard link āĻāĻ•āĻ‡ inode-āĻāĻ° āĻĻāĻŋāĻ•ā§‡ āĻ¨āĻŋāĻ°ā§āĻĻā§‡āĻļ āĻ•āĻ°ā§‡; symbolic link āĻāĻ•āĻŸāĻŋ path reference āĻ•āĻ°ā§‡ āĻāĻŦāĻ‚ āĻ†āĻ˛āĻžāĻĻāĻž inode āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻ•āĻ°ā§‡āĨ¤

Q12. Zombie process āĻ•ā§€?

Child process terminate āĻ•āĻ°ā§‡āĻ›ā§‡ āĻ•āĻŋāĻ¨ā§āĻ¤ā§ parent āĻ¤āĻžāĻ° exit status collect āĻ•āĻ°ā§‡āĻ¨āĻŋ—āĻ¤āĻ–āĻ¨ zombie state āĻšāĻ¤ā§‡ āĻĒāĻžāĻ°ā§‡āĨ¤

Q13. Load average āĻ•ā§€?

System-āĻāĻ° runnable āĻāĻŦāĻ‚ āĻ•āĻŋāĻ›ā§ uninterruptible work-āĻāĻ° queue/load-āĻāĻ° āĻāĻ•āĻŸāĻŋ time-windowed indicationāĨ¤

Q14. /proc āĻ•ā§€?

Kernel āĻāĻŦāĻ‚ process information expose āĻ•āĻ°āĻž virtual filesystemāĨ¤

Q15. df āĻāĻŦāĻ‚ du difference? 

df → filesystem-level disk usage
du → directory/file-level usage
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Q16. systemctl āĻ•ā§€?

systemd-managed services āĻāĻŦāĻ‚ system state control āĻ•āĻ°āĻžāĻ° commandāĨ¤

Q17. journalctl āĻ•ā§€?

systemd journal-āĻāĻ° logs query āĻ•āĻ°āĻžāĻ° toolāĨ¤

Q18. ss āĻ•ā§€?

Network sockets āĻāĻŦāĻ‚ listening connections inspect āĻ•āĻ°āĻžāĻ° toolāĨ¤

100. Advanced Interview Questions

Q19. Linux-āĻ āĻāĻ•āĻŸāĻŋ process CPU 100% āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻ•āĻ°āĻ˛ā§‡ āĻ•ā§€āĻ­āĻžāĻŦā§‡ troubleshoot āĻ•āĻ°āĻŦā§‡? 

top/htop
   ↓
identify PID
   ↓
ps
   ↓
inspect process
   ↓
logs
   ↓
application behavior
   ↓
profiling/metrics
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Q20. Disk 100% fullāĨ¤ āĻ•ā§€ āĻ•āĻ°āĻŦā§‡? 

df -h
du -sh /*
find /var -type f -size +1G
df -i
lsof +L1
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āĻ¤āĻžāĻ°āĻĒāĻ° identify āĻ•āĻ°ā§‡ safe cleanupāĨ¤

Q21. Port 8080 already in useāĨ¤ āĻ•ā§€ āĻ•āĻ°āĻŦā§‡? 

ss -lntp | grep :8080
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āĻ…āĻĨāĻŦāĻž:

lsof -i :8080
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āĻ¤āĻžāĻ°āĻĒāĻ° owning process identify āĻ•āĻ°ā§‡ root cause āĻ…āĻ¨ā§āĻ¯āĻžā§Ÿā§€ āĻŦā§āĻ¯āĻŦāĻ¸ā§āĻĨāĻž āĻ¨ā§‡āĻŦāĨ¤

Q22. Server ping āĻ•āĻ°āĻž āĻ¯āĻžāĻšā§āĻ›ā§‡ āĻ•āĻŋāĻ¨ā§āĻ¤ā§ application access āĻ•āĻ°āĻž āĻ¯āĻžāĻšā§āĻ›ā§‡ āĻ¨āĻžāĨ¤ āĻ•ā§‡āĻ¨?

Possible layers:

DNS
Firewall
Port
Service
Application
Reverse Proxy
Routing
Security Group
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Q23. Nginx 502 āĻĻāĻŋāĻšā§āĻ›ā§‡āĨ¤ āĻ•ā§€āĻ­āĻžāĻŦā§‡ troubleshoot āĻ•āĻ°āĻŦā§‡? 

Nginx status
    ↓
Nginx logs
    ↓
Backend service
    ↓
Backend port
    ↓
curl backend directly
    ↓
Application logs
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Q24. Memory āĻļā§‡āĻˇ āĻšā§Ÿā§‡ āĻ—ā§‡āĻ˛ā§‡ Linux āĻ•ā§€ āĻ•āĻ°āĻ¤ā§‡ āĻĒāĻžāĻ°ā§‡?

System swap āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻ•āĻ°āĻ¤ā§‡ āĻĒāĻžāĻ°ā§‡; extreme memory pressure-āĻ OOM killer process terminate āĻ•āĻ°āĻ¤ā§‡ āĻĒāĻžāĻ°ā§‡āĨ¤

Q25. Docker container-āĻāĻ° Linux process āĻ•ā§‡āĻ¨ host-āĻāĻ° kernel āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻ•āĻ°ā§‡?

Containers āĻ¸āĻžāĻ§āĻžāĻ°āĻŖāĻ¤ full VM āĻ¨ā§Ÿ; Linux kernel-āĻāĻ° isolation primitives āĻ¯ā§‡āĻŽāĻ¨ namespaces āĻāĻŦāĻ‚ cgroups āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻ•āĻ°ā§‡ process/environment isolate āĻ•āĻ°ā§‡āĨ¤

101. Scenario-Based Interview

Scenario 1

Production API suddenly returning 500.

āĻ¤ā§āĻŽāĻŋ āĻŦāĻ˛āĻŦā§‡:

1. Check application logs
2. Check recent deployment
3. Check dependencies
4. Check CPU/memory/disk
5. Check database/network
6. Reproduce request
7. Rollback if necessary
8. Verify recovery
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Scenario 2

API latency suddenly increased.

Check:

CPU
Memory
Load
Network
Disk I/O
Database latency
Upstream services
Application logs
Recent changes
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Scenario 3

Server disk full.

Check:

df -h
du -sh /var/*
df -i
lsof +L1
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Common causes:

Logs
Docker
Backups
Temporary files
Deleted open files
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Scenario 4

Kubernetes Pod āĻŦāĻžāĻ°āĻŦāĻžāĻ° restart āĻ•āĻ°āĻ›ā§‡āĨ¤

Linux-level āĻāĻŦāĻ‚ Kubernetes-level āĻĻā§āĻŸā§‹ āĻĻāĻŋāĻ•:

kubectl logs
kubectl describe pod
        ↓
Application logs
        ↓
OOM?
CPU?
Configuration?
Dependency?
        ↓
Node health
        ↓
journalctl
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102. Hands-on Lab 1 — Linux Server

āĻāĻ•āĻŸāĻŋ VM āĻŦāĻž cloud server āĻ¤ā§ˆāĻ°āĻŋ āĻ•āĻ°ā§‡:

Ubuntu
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Install:

nginx
git
docker
curl
htop
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āĻ¤āĻžāĻ°āĻĒāĻ°:

  • SSH āĻ•āĻ°ā§‹
  • user āĻ¤ā§ˆāĻ°āĻŋ āĻ•āĻ°ā§‹
  • permissions change āĻ•āĻ°ā§‹
  • Nginx āĻšāĻžāĻ˛āĻžāĻ“
  • logs āĻĻā§‡āĻ–ā§‹
  • port check āĻ•āĻ°ā§‹

103. Hands-on Lab 2 — Nginx

Install:

sudo apt install nginx
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Check:

systemctl status nginx
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Test:

curl localhost
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Port:

ss -lntp | grep :80
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Logs:

journalctl -u nginx
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104. Hands-on Lab 3 — Deploy FastAPI

Flow:

Linux VM
   ↓
Python
   ↓
FastAPI
   ↓
Uvicorn
   ↓
Nginx
   ↓
Internet
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āĻāĻŸāĻž āĻ¤ā§‹āĻŽāĻžāĻ° ML inference platform-āĻāĻ° foundation āĻšāĻŋāĻ¸ā§‡āĻŦā§‡ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻ•āĻ°āĻ¤ā§‡ āĻĒāĻžāĻ°ā§‹āĨ¤

105. Hands-on Lab 4 — Monitoring

āĻāĻ•āĻŸāĻŋ application āĻšāĻžāĻ˛āĻŋā§Ÿā§‡:

top
free -h
df -h
ss -lntp
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observe āĻ•āĻ°āĻŦā§‡āĨ¤

āĻ¤āĻžāĻ°āĻĒāĻ° artificial load āĻ¤ā§ˆāĻ°āĻŋ āĻ•āĻ°ā§‡ CPU/memory behavior āĻĻā§‡āĻ–āĻŦā§‡āĨ¤

106. Hands-on Lab 5 — Bash Automation

āĻāĻ•āĻŸāĻŋ script āĻŦāĻžāĻ¨āĻžāĻ“:

backup.sh
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āĻ¯āĻž:

1. Application directory backup āĻ•āĻ°āĻŦā§‡
2. Timestamp āĻ¯ā§‹āĻ— āĻ•āĻ°āĻŦā§‡
3. tar.gz āĻŦāĻžāĻ¨āĻžāĻŦā§‡
4. āĻĒā§āĻ°āĻ¨ā§‹ backup delete āĻ•āĻ°āĻŦā§‡
5. success/failure log āĻ•āĻ°āĻŦā§‡
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āĻ¤āĻžāĻ°āĻĒāĻ° cron āĻĻāĻŋā§Ÿā§‡ schedule āĻ•āĻ°ā§‹āĨ¤

107. Hands-on Lab 6 — Linux Troubleshooting

āĻ¨āĻŋāĻœā§‡ intentionally problem āĻ¤ā§ˆāĻ°āĻŋ āĻ•āĻ°ā§‹:

Stop nginx
Kill application
Fill temporary disk
Block a port
Wrong permissions
Wrong environment variable
Wrong DNS entry
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āĻ¤āĻžāĻ°āĻĒāĻ° āĻ¨āĻŋāĻœā§‡ troubleshoot āĻ•āĻ°ā§‹āĨ¤

āĻāĻŸāĻž interview preparation-āĻāĻ° āĻœāĻ¨ā§āĻ¯ āĻ¸āĻŦāĻšā§‡ā§Ÿā§‡ valuable exerciseāĻ—ā§āĻ˛ā§‹āĻ° āĻāĻ•āĻŸāĻŋāĨ¤

108. DevOps Linux Skill Matrix

Topic Priority
Linux basics ⭐⭐⭐⭐⭐
Filesystem ⭐⭐⭐⭐⭐
Permissions ⭐⭐⭐⭐⭐
Users/Groups ⭐⭐⭐⭐⭐
Processes ⭐⭐⭐⭐⭐
Networking ⭐⭐⭐⭐⭐
SSH ⭐⭐⭐⭐⭐
systemd ⭐⭐⭐⭐⭐
Logs ⭐⭐⭐⭐⭐
Bash ⭐⭐⭐⭐⭐
Docker/Linux relationship ⭐⭐⭐⭐⭐
Troubleshooting ⭐⭐⭐⭐⭐
Disk/storage ⭐⭐⭐⭐
Security ⭐⭐⭐⭐
DNS ⭐⭐⭐⭐
TCP/IP ⭐⭐⭐⭐
Nginx ⭐⭐⭐⭐
cron ⭐⭐⭐
awk/sed ⭐⭐⭐
tcpdump ⭐⭐⭐
SELinux/AppArmor ⭐⭐⭐

109. 30-Day Linux → DevOps Foundation Plan

Week 1 — Linux Basics 

Day 1
Linux + filesystem

Day 2
Navigation + file management

Day 3
Permissions + ownership

Day 4
Users + groups + sudo

Day 5
Processes + signals

Day 6
Package management

Day 7
Revision + practical lab
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Week 2 — Linux Administration 

Day 8
Environment variables

Day 9
Bash basics

Day 10
grep + pipes

Day 11
awk + sed

Day 12
systemd

Day 13
journalctl + logs

Day 14
cron + automation
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Week 3 — Networking + Storage 

Day 15
IP + subnet basics

Day 16
TCP/UDP + ports

Day 17
DNS

Day 18
SSH

Day 19
curl + wget + nc

Day 20
Disk + filesystem

Day 21
mount + inode + troubleshooting
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Week 4 — DevOps Linux 

Day 22
Nginx

Day 23
Reverse proxy

Day 24
Linux security

Day 25
Docker + Linux

Day 26
Kubernetes + Linux

Day 27
Performance troubleshooting

Day 28
Production troubleshooting

Day 29
Interview preparation

Day 30
Complete practical project
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110. Final Linux Project

āĻāĻ•āĻŸāĻŋ complete mini-production environment āĻŦāĻžāĻ¨āĻžāĻ“:

                    Internet
                       |
                       v
                    Nginx
                       |
                       v
                   FastAPI
                       |
                       v
                  ML Model
                       |
                  +----+----+
                  |         |
                Logs      Metrics
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Server-āĻ:

Ubuntu
Nginx
FastAPI
systemd
SSH
Firewall
Bash
cron
logging
monitoring
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Implement:

  • [ ] SSH authentication
  • [ ] Non-root application user
  • [ ] FastAPI service
  • [ ] systemd service
  • [ ] Nginx reverse proxy
  • [ ] HTTPS
  • [ ] firewall
  • [ ] log rotation
  • [ ] backup script
  • [ ] cron
  • [ ] monitoring
  • [ ] troubleshooting documentation

111. Final Interview Checklist

Interview-āĻāĻ° āĻ†āĻ—ā§‡ confidently explain āĻ•āĻ°āĻ¤ā§‡ āĻĒāĻžāĻ°āĻŦā§‡:

Linux

  • [ ] Linux architecture
  • [ ] Kernel
  • [ ] Filesystem
  • [ ] /etc
  • [ ] /var
  • [ ] /proc
  • [ ] permissions
  • [ ] users/groups
  • [ ] sudo

Processes

  • [ ] PID
  • [ ] signals
  • [ ] zombie
  • [ ] orphan
  • [ ] process vs thread
  • [ ] CPU troubleshooting
  • [ ] memory troubleshooting

Networking

  • [ ] IP
  • [ ] subnet
  • [ ] routing
  • [ ] TCP/UDP
  • [ ] DNS
  • [ ] ports
  • [ ] sockets
  • [ ] HTTP/HTTPS
  • [ ] firewall

Administration

  • [ ] SSH
  • [ ] systemd
  • [ ] journalctl
  • [ ] cron
  • [ ] package management
  • [ ] storage
  • [ ] mount
  • [ ] inode

DevOps

  • [ ] Linux + Docker
  • [ ] Linux + Kubernetes
  • [ ] Nginx
  • [ ] reverse proxy
  • [ ] Bash automation
  • [ ] monitoring
  • [ ] troubleshooting
  • [ ] security

đŸŽ¯ Final Goal

Linux āĻļā§‡āĻ–āĻžāĻ° āĻ‰āĻĻā§āĻĻā§‡āĻļā§āĻ¯ āĻļā§āĻ§ā§ command āĻŽā§āĻ–āĻ¸ā§āĻĨ āĻ•āĻ°āĻž āĻ¨ā§ŸāĨ¤

āĻ¤ā§‹āĻŽāĻžāĻ° goal āĻšāĻŦā§‡:

"I can operate and troubleshoot a Linux production server."
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āĻ¤āĻžāĻ°āĻĒāĻ°:

Linux
   ↓
Git
   ↓
Docker
   ↓
Kubernetes
   ↓
Terraform
   ↓
GitHub Actions
   ↓
ArgoCD
   ↓
Prometheus/Grafana
   ↓
Production DevOps
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Linux-āĻāĻ° āĻ•ā§āĻˇā§‡āĻ¤ā§āĻ°ā§‡ āĻŦāĻŋāĻļā§‡āĻˇ āĻ•āĻ°ā§‡ command āĻŽā§āĻ–āĻ¸ā§āĻĨ āĻ•āĻ°āĻžāĻ° āĻšā§‡ā§Ÿā§‡ troubleshooting skill āĻŦā§‡āĻļāĻŋ āĻ—ā§āĻ°ā§āĻ¤ā§āĻŦāĻĒā§‚āĻ°ā§āĻŖāĨ¤

āĻāĻ•āĻœāĻ¨ DevOps engineer āĻšāĻŋāĻ¸ā§‡āĻŦā§‡ āĻ¤ā§āĻŽāĻŋ āĻ¯ā§‡āĻ¨ āĻāĻ•āĻŸāĻŋ āĻ¸āĻŽāĻ¸ā§āĻ¯āĻž āĻĻā§‡āĻ–ā§‡ āĻŦāĻ˛āĻ¤ā§‡ āĻĒāĻžāĻ°ā§‹:

What is broken?
        ↓
Where is it broken?
        ↓
Why is it broken?
        ↓
How can I verify it?
        ↓
How can I fix it safely?
        ↓
How can I prevent it from happening again?
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āĻāĻŸāĻžāĻ‡ āĻāĻ‡ Linux roadmap-āĻāĻ° āĻŽā§‚āĻ˛ āĻ˛āĻ•ā§āĻˇā§āĻ¯āĨ¤

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