Linux Essentials for DevOps Engineers

Linux is the backbone of modern infrastructure. Whether you're managing servers, containers, or cloud resources, Linux skills are essential.

File System Navigation

# Print working directory
pwd

# List files with details
ls -la

# Change directory
cd /var/log

# Create directories
mkdir -p /opt/myapp/{bin,config,logs}

# Find files
find /var -name "*.log" -mtime -7

# Search file contents
grep -r "error" /var/log/

File Operations

# Copy files
cp source.txt destination.txt
cp -r source_dir/ destination_dir/

# Move/rename files
mv oldname.txt newname.txt

# Remove files
rm -rf directory/  # Use with caution!

# View file contents
cat file.txt
less file.txt
head -n 20 file.txt
tail -f /var/log/syslog  # Follow log in real-time

User and Permission Management

# View current user
whoami

# Switch user
sudo su - username

# Add user
sudo useradd -m -s /bin/bash newuser

# Change file permissions
chmod 755 script.sh
chmod u+x script.sh

# Change ownership
chown user:group file.txt
chown -R user:group directory/

# View permissions
ls -la
# drwxr-xr-x = directory, owner rwx, group rx, others rx

Process Management

# View running processes
ps aux
ps aux | grep nginx

# Real-time process monitor
top
htop

# Kill a process
kill -9 PID
pkill -f process_name

# Background processes
./long_running_script.sh &
nohup ./script.sh > output.log 2>&1 &

# View jobs
jobs
fg %1  # Bring to foreground

Networking

# Network interfaces
ip addr
ifconfig

# Test connectivity
ping google.com
traceroute google.com

# DNS lookup
nslookup google.com
dig google.com

# Active connections
netstat -tuln
ss -tuln

# Download files
curl -O https://example.com/file.tar.gz
wget https://example.com/file.tar.gz

# Transfer files
scp file.txt user@remote:/path/
rsync -avz source/ user@remote:/destination/

System Information

# System info
uname -a
hostnamectl

# Memory usage
free -h

# Disk usage
df -h
du -sh /var/log/*

# CPU info
lscpu
cat /proc/cpuinfo

Shell Scripting Basics

#!/bin/bash
# Simple deployment script

set -e  # Exit on error

APP_NAME="myapp"
DEPLOY_DIR="/opt/$APP_NAME"
BACKUP_DIR="/opt/backups"

echo "Starting deployment..."

# Create backup
timestamp=$(date +%Y%m%d_%H%M%S)
tar -czf "$BACKUP_DIR/${APP_NAME}_${timestamp}.tar.gz" "$DEPLOY_DIR"

# Deploy new version
cd "$DEPLOY_DIR"
git pull origin main
npm install --production
pm2 restart $APP_NAME

echo "Deployment complete!"

Package Management

# Debian/Ubuntu (apt)
sudo apt update
sudo apt install nginx
sudo apt remove nginx
sudo apt autoremove

# RHEL/CentOS (yum/dnf)
sudo dnf update
sudo dnf install nginx
sudo dnf remove nginx

Essential Tools

Tool	Purpose
vim/nano	Text editors
tmux/screen	Terminal multiplexer
jq	JSON processor
awk/sed	Text processing
systemctl	Service management

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Master these fundamentals and you'll be ready for any DevOps challenge!