🐧 Linux Commands Cheatsheet: Essential Commands for DevOps

Linux Commands Cheatsheet for DevOps Engineers

A comprehensive collection of essential Linux commands organized by category, with practical examples and common DevOps use cases.

System Information & Monitoring

System Status Commands

Command	Example	Use Case
`top`	`top -c -p $(pgrep nginx \\| tr "\\n" "," \\| sed 's/,$/\\n/')`	Monitor nginx process resources
`htop`	`htop -u www-data`	Interactive process monitoring for web server
`free`	`free -h --seconds 5`	Monitor memory usage in real-time
`df`	`df -h --output=source,fstype,size,used,avail,pcent,target`	Check disk space across mounts
`vmstat`	`vmstat 1 100`	Monitor system performance

Hardware Information

Command	Example	Use Case
`lscpu`	`lscpu --json`	CPU information for automation
`dmidecode`	`dmidecode --type memory`	Hardware inventory
`lsblk`	`lsblk --json --output NAME,SIZE,MOUNTPOINT`	Storage device mapping
`iostat`	`iostat -xz 1`	Monitor disk I/O performance

Process Management

Process Control

Command	Example	Use Case
`ps`	`ps aux --sort=-%cpu \\| head -10`	Find CPU-intensive processes
`kill`	`kill -9 $(lsof -t -i:8080)`	Kill process on specific port
`nice`	`nice -n 10 ./backup-script.sh`	Run backup with lower priority
`pgrep`	`pgrep -f "java.production." \\| xargs kill`	Find and kill Java processes

Service Management

Command	Example	Use Case
`systemctl`	`systemctl list-units --type=service --state=running`	Monitor running services
`journalctl`	`journalctl -u nginx -f --since "5m ago"`	Real-time service logs
`service`	`service --status-all \\| grep "+"`	List active services

File Operations

File Management

Command	Example	Use Case
`find`	`find /var/log -type f -mtime +30 -delete`	Clean old log files
`tar`	`tar czf "backup-$(date +%F).tar.gz" /var/www/`	Create dated backups
`rsync`	`rsync -avz --progress /src/ user@remote:/dest/`	Incremental file sync
`dd`	`dd if=/dev/zero of=/swapfile bs=1M count=1024 status=progress`	Create swap file

File Monitoring

Command	Example	Use Case
`tail`	`tail -f /var/log/nginx/error.log \\| grep -i error`	Monitor logs for errors
`watch`	`watch -n 1 'ls -l /var/log \\| grep "$(date +%Y-%m-%d)"'`	Monitor file changes
`inotifywait`	`inotifywait -m /var/www -e create -e modify`	Monitor directory changes

Network Operations

Network Monitoring

Command	Example	Use Case
`netstat`	`netstat -tulpn \\| grep LISTEN`	Check listening ports
`ss`	`ss -tuln \\| grep ":80"`	Modern socket statistics
`iftop`	`iftop -i eth0 -P`	Monitor network bandwidth
`tcpdump`	`tcpdump -i any port 80 -w capture.pcap`	Capture HTTP traffic

Network Configuration

Command	Example	Use Case
`ip`	`ip -br addr show`	Quick network interface status
`curl`	`curl -w "%{http_code}" -o /dev/null -s http://localhost`	HTTP endpoint monitoring
`dig`	`dig +short mx example.com`	DNS troubleshooting
`nmap`	`nmap -sS -p- localhost`	Security port scanning

User Management

User Operations

Command	Example	Use Case
`useradd`	`useradd -m -s /bin/bash -G docker,sudo newdev`	Create developer account
`usermod`	`usermod -aG docker jenkins`	Add service account to group
`chown`	`chown -R www-data:www-data /var/www/`	Fix web folder permissions
`chmod`	`chmod -R u=rwX,g=rX,o= /etc/ssl/private/`	Secure SSL keys

Access Control

Command	Example	Use Case
`sudo`	`sudo -l -U jenkins`	Audit user privileges
`last`	`last -10`	Check recent logins
`who`	`who -a`	Show active users

Storage Management

Disk Operations

Command	Example	Use Case
`fdisk`	`fdisk -l \\| grep "Disk /dev"`	List available disks
`parted`	`parted -l \\| grep "Disk /dev"`	Modern partition management
`mount`	`mount -o remount,rw /`	Remount filesystem RW
`lvm`	`lvextend -l +100%FREE -r /dev/mapper/vg-root`	Extend LVM volume

File System

Command	Example	Use Case
`du`	`du -sh /* \\| sort -hr`	Find large directories
`ncdu`	`ncdu /var`	Interactive disk usage
`xfs_repair`	`xfs_repair -v /dev/sda1`	Repair XFS filesystem

Performance Tuning

Resource Limits

Command	Example	Use Case
`ulimit`	`ulimit -n 65535`	Increase file descriptors
`sysctl`	`sysctl -w vm.swappiness=10`	Adjust kernel parameters
`nice`	`nice -n -10 ./critical-service`	Increase process priority

Performance Monitoring

Command	Example	Use Case
`sar`	`sar -q 1 60`	Monitor system load
`pidstat`	`pidstat -d 1`	Monitor per-process I/O
`strace`	`strace -f -p $(pidof nginx)`	Debug process syscalls

Text Processing

Log Analysis

Command	Example	Use Case
`grep`	`grep -R "ERROR" /var/log/ --include="*.log"`	Find errors in logs
`awk`	`awk '$9 >= 500 {print $7}' access.log \\| sort \\| uniq -c`	Analyze HTTP 5xx errors
`sed`	`sed -i 's/DEBUG/INFO/g' application.properties`	Bulk text replacement

Text Manipulation

Command	Example	Use Case
`cut`	`cut -d',' -f1,3 data.csv`	Extract CSV columns
`sort`	`sort -k2 -n data.txt`	Sort numerical data
`uniq`	`sort access.log \\| uniq -c \\| sort -nr`	Count unique entries

System Maintenance

Package Management

Command	Example	Use Case
`apt`	`apt list --upgradable`	Check available updates
`dpkg`	`dpkg -l \\| grep security`	List security packages
`snap`	`snap list --all \\| grep disabled`	Clean old snap versions

System Updates

Command	Example	Use Case
`apt-get`	`apt-get update && apt-get upgrade -y`	System update
`do-release-upgrade`	`do-release-upgrade -d`	Distribution upgrade
`needrestart`	`needrestart -r a`	Check required restarts

Automation Tips

Scripting Helpers

Command	Example	Use Case
`cron`	`(crontab -l 2>/dev/null; echo "0 2 * * * /backup.sh") \\| crontab -`	Add backup schedule
`at`	`echo "./deploy.sh" \\| at midnight`	Schedule one-time task
`expect`	`expect -c 'spawn ssh user@host; expect "password:"; send "pass\n"'`	Automate interactive

One-liners

# Find and kill memory-hungry processes
ps aux | awk 'NR>1{if($4>5.0) print $2}' | xargs kill

# Clean old Docker resources
docker system prune --volumes -af

# Find large files
find / -type f -size +100M -exec ls -lh {} \;

# Monitor failed SSH attempts
tail -f /var/log/auth.log | grep --line-buffered "Failed password"

Best Practices

Always Use Version Control

# Create timestamped backups
cp config.ini{,.$(date +%Y%m%d_%H%M%S).bak}

Secure Sensitive Operations

# Set secure permissions
umask 077; echo "secret" > credentials.txt

Monitor Resource Usage

# Custom PS1 with load average
export PS1='[\l] \u@\h:\w\$ '