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Useful Commands - Cheat Sheet

I have collected all my usefull commands in one place.

Linux Commands Cheatsheet

A comprehensive collection of useful Linux commands for system administration, development, and everyday tasks.

Table of Contents

  • System Management
  • File Operations
  • Networking
  • Process Management
  • Service Management
  • Compression and Archiving
  • Permissions
  • Package Management
  • System Information
  • Docker
  • Java Development
  • Maven
  • Spring Boot
  • Useful Aliases

System Management

Update and Upgrade

# Update the package lists
sudo apt-get update

# Upgrade installed packages
sudo apt upgrade -y

# Update and upgrade in one command
sudo apt update && sudo apt upgrade -y

Firewall Setup

# Install the Uncomplicated Firewall
sudo apt install ufw -y

# Enable the firewall
sudo ufw enable

# Allow common ports
sudo ufw allow 80       # HTTP
sudo ufw allow 443      # HTTPS
sudo ufw allow 22       # SSH
sudo ufw allow ssh      # SSH (alternative)

Reboot and Shutdown

# Reboot the system
sudo reboot

# Power off the system
sudo poweroff

# Halt the system
sudo halt

# Shutdown with options
sudo shutdown

File Operations

Viewing Files

# Display file contents
cat file.txt

# View file with pagination
less file.txt

# View last lines of file (follow mode)
tail -f file.log

# View last 1000 lines and follow updates
tail -n 1000 -f file.log

Creating and Modifying Files

# Write to a file (overwrites existing content)
echo "text" > file.txt

# Append to a file
echo "text" >> file.txt

File Management

# Copy a file
cp source_file destination_file

# Move or rename a file
mv source_file destination_file

# Remove a file
rm file.txt

# Find a file by name
find /path -name "filename"

# Search inside files for a string
grep -r "text_to_search" /path/to/search

# Colorize grep output
grep --color=auto "pattern" file

Networking

Network Information

# Install network tools
sudo apt install net-tools

# Check IP address
ip addr show

# Alternative for IP address
ifconfig

# Ping a host
ping example.com

# Display routing table
netstat -rn

# List all TCP connections with ports and processes
sudo netstat -tnlp

# Find process using specific port
sudo netstat -tnlp | grep :22
sudo netstat -tnlp | grep :8080

Port Management

# Install lsof
sudo apt-get install lsof

# Find which app is using a port
sudo lsof -i :PORT_NUMBER
# Example: sudo lsof -i :8080

# Kill an app using a port
sudo kill -9 $(sudo lsof -t -i :PORT_NUMBER)

Process Management

Process Monitoring

# List all running processes
ps aux

# Interactive process viewer
top

# Sort processes by memory usage
ps auxf | sort -nr -k 4

# Top 10 processes by memory usage
ps auxf | sort -nr -k 4 | head -10

# Sort processes by CPU usage
ps auxf | sort -nr -k 3

# Top 10 processes by CPU usage
ps auxf | sort -nr -k 3 | head -10

# Find Java/Spring Boot processes
ps aux | grep java
ps aux | grep spring-boot

Process Control

# Kill a process by PID
kill -9 PID

Service Management

Systemd Commands

# Check status of all services
service --status-all

# Check status of a specific service
sudo systemctl status service_name

# Start a service
sudo systemctl start service_name

# Stop a service
sudo systemctl stop service_name

# Restart a service
sudo systemctl restart service_name

# Enable a service at boot
sudo systemctl enable service_name

# Disable a service at boot
sudo systemctl disable service_name

Nginx Commands

# Test Nginx configuration
nginx -t

# Restart Nginx
systemctl restart nginx

Compression and Archiving

Tar Commands

# Compress files (tar.gz)
tar -czvf archive.tar.gz file1 file2

# Extract tar.gz files
tar -xzvf archive.tar.gz

Zip Commands

# Zip a file
zip archive.zip file1 file2

# Unzip a file
unzip archive.zip

Permissions

# Change permissions of a file
chmod 755 file.txt

# Change ownership of a file
sudo chown user:user file.txt

# Change permissions recursively
chmod -R 755 /path/to/directory

Package Management

Debian/Ubuntu (apt)

# Update the package list
sudo apt update

# Upgrade all packages
sudo apt upgrade

# Install a package
sudo apt install package_name

# Uninstall a package
sudo apt remove package_name

# Purge a package (completely remove config files as well)
sudo apt purge package_name

# Search for a package
apt search package_name

System Information

# Check disk usage
df -h

# Check memory usage
free -h

# Free memory info
free -m -l -t

# Check CPU usage
top

# Check system uptime
uptime

# CPU information
lscpu

# GPU memory information
grep -i --color memory /var/log/Xorg.0.log

Docker

Image Management

# Pull an image from Docker Hub
docker pull image_name

# View all images
docker images

# Remove an image
docker rmi image_name

# Build an image from a Dockerfile
docker build -t image_name .

# Remove dangling/unused images
docker image prune

Container Management

# Run a Docker container
docker run image_name

# Run with options
docker run -d -p host_port:container_port --name container_name image_name

# List running containers
docker ps

# List all containers (including stopped)
docker ps -a

# Stop a running container
docker stop container_name_or_id

# Start a stopped container
docker start container_name_or_id

# Remove a stopped container
docker rm container_name_or_id

# Check logs of a container
docker logs container_name_or_id

# Follow container logs with limited output
docker logs --follow --tail=50 container_name_or_id

# Exec into a running container
docker exec -it container_name_or_id /bin/bash

# Stop and remove all containers
docker stop $(docker ps -a -q) && docker rm $(docker ps -a -q)

Java Development

# Compile a Java file
javac MyClass.java

# Run a compiled Java class
java MyClass

# Run a JAR file
java -jar myapp.jar

# Set classpath for external libraries
java -cp .:path_to_lib/library.jar MyClass

# Check Java version
java -version

Maven

# Clean the target directory
mvn clean

# Compile the source code
mvn compile

# Run unit tests
mvn test

# Package the project
mvn package

# Clean and build the project
mvn clean install

# analyze dependencies
mvn dependency:analyze

# Skip tests during build
mvn clean install -DskipTests
mvn clean install -DskipTests=true

# Check for updates of dependencies
mvn versions:display-dependency-updates

Spring Boot

# Run a Spring Boot application (packaged as JAR)
java -jar target/myapp.jar

# Run from source using Maven
mvn spring-boot:run

# Run in background with output to log file
nohup mvn spring-boot:run > app.log 2>&1 &

# Run in background with timestamped log file
nohup mvn spring-boot:run > "app_$(date '+%Y-%m-%d_%H-%M-%S').log" 2>&1 &

# Skip tests during build
mvn clean install -DskipTests=true

# Run in background
nohup mvn spring-boot:run &

# Generate a Spring Boot project
curl https://start.spring.io/starter.zip -d dependencies=web -o demo.zip

# Run with active profile
java -jar target/myapp.jar --spring.profiles.active=dev

# Run with debugging enabled
mvn spring-boot:run -Dspring-boot.run.fork=false -X

Useful Aliases

Add these to your /etc/bash.bashrc file for system-wide aliases or ~/.bashrc for user-specific aliases:

# File listing aliases
alias ll='ls -al'                # List all files in long format
alias lll='ls -alh'              # List all files with human-readable sizes
alias lt='ls --human-readable --size -1 -S --classify'  # Sort by size

# Navigation shortcuts
alias cls='clear'                # Clear the screen
alias ..='cd ..'                 # Go up one directory
alias ...='cd ../../../'         # Go up three directories
alias ....='cd ../../../../'     # Go up four directories

# Package management shortcuts
alias yep='sudo apt install'     # Simplified installation
alias nop='sudo apt remove'      # Simplified removal
alias update='sudo apt update && sudo apt upgrade -y'  # Update and upgrade

# System commands
alias reboot='sudo /sbin/reboot'
alias poweroff='sudo /sbin/poweroff'
alias halt='sudo /sbin/halt'
alias shutdown='sudo /sbin/shutdown'

# Network monitoring
alias whatsup='service --status-all'  # Check all services status
alias iftop='iftop -i eth1'

# System information
alias meminfo='free -m -l -t'         # Memory information
alias path='echo -e ${PATH//:/\\n}'    # Show PATH entries one per line
alias now='date +"%T"'                # Current time
alias nowtime=now
alias nowdate='date +"%d-%m-%Y"'      # Current date

# Process monitoring
alias psmem='ps auxf | sort -nr -k 4'     # Sort processes by memory usage
alias psmem10='ps auxf | sort -nr -k 4 | head -10'  # Top 10 by memory
alias pscpu='ps auxf | sort -nr -k 3'     # Sort processes by CPU usage
alias pscpu10='ps auxf | sort -nr -k 3 | head -10'  # Top 10 by CPU

# System information
alias cpuinfo='lscpu'            # CPU information
alias gpumeminfo='grep -i --color memory /var/log/Xorg.0.log'  # GPU memory info

# Enhanced command defaults
alias grep='grep --color=auto'   # Colorize grep output

To add these aliases and make them available immediately:

# Add to global bashrc (requires sudo)
sudo echo "... aliases here ..." >> /etc/bash.bashrc

# Or add to user's bashrc
echo "... aliases here ..." >> ~/.bashrc

# Update aliases in the current session
source ~/.bashrc

Shell Script Creation & Execution

# Create and run a shell script
echo '#!/bin/bash
echo "Hello, World!"' > script.sh && chmod +x script.sh && ./script.sh

# Make a script executable
chmod +x deploy.sh

find . | sed -e "s/[^-][^\/]*\//  |/g" -e "s/|\([^ ]\)/|-\1/"
Gitignore
git ignore for all files
.gitignore
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