# Find files by name
find . -name "*.js" -type f
find /var/log -name "*.log" -mtime -7    # Modified in last 7 days

# Search file contents
grep -r "TODO" src/                       # Recursive search
grep -rn "function" src/                  # With line numbers
grep -r "error" /var/log/ --include="*.log" # In specific files only

# Quick find (faster than find for name searches)
locate config.json                        # Updatedb first
fd pattern src/                           # Install: apt install fd-find

# Better grep (ripgrep)
rg "TODO" src/                            # Faster, ignores .gitignore

# Disk usage
df -h                                     # Human-readable disk usage
du -sh *                                  # Directory sizes in current folder
du -sh /var/* | sort -hr | head -10       # Top 10 largest directories

# Find large files
find . -size +100M -type f                # Files > 100MB
find . -size +1G -exec ls -lh {} \;       # Show details of huge files

# Memory
free -h                                   # RAM usage
top                                       # Process resource usage (or htop)
ps aux | sort -k4nr | head -10            # Top 10 memory-hungry processes

# Port checking
ss -tlnp | grep :3000                     # What's listening on port 3000?
netstat -tlnp                             # All listening ports

# Connection testing
curl -I https://example.com               # Headers only
curl -s -o /dev/null -w "%{http_code}" URL # Just status code
wget -qO- https://ifconfig.me             # Your public IP

# DNS
dig example.com                            # DNS lookup
nslookup example.com                      # Alternative DNS check
host example.com                          # Simple DNS query

# Debug connectivity
ping -c 4 google.com                      # 4 pings
traceroute google.com                     # Route to destination
telnet host 80                            # Test TCP connection
nc -zv localhost 3000                     # Check if port is open

# Find and kill
ps aux | grep node                        # Find node processes
kill 12345                                # Graceful kill
kill -9 12345                             # Force kill
pkill -f "node server.js"                # Kill by pattern

# Background processes
node server.js &                          # Run in background
jobs                                      # List background jobs
fg %1                                     # Bring job 1 to front
bg %1                                     # Resume suspended job in background
nohup node server.js &                   # Survives logout

# Monitor process
watch -n 2 'curl -s http://localhost:3000/health' # Repeat every 2 seconds
tail -f /var/log/app.log                 # Follow log file

# View files
less bigfile.txt                          # Scrollable viewer (q to quit)
head -20 file.txt                         # First 20 lines
tail -50 file.txt                         # Last 50 lines
tail -f logfile.txt                       # Live follow

# Count
wc -l file.txt                            # Line count
wc -w file.txt                            # Word count
grep -c "error" logfile.txt              # Count matches

# Sort & unique
sort file.txt                             # Sort lines
sort -u file.txt                          # Unique lines
sort file.txt | uniq -c                   # Count occurrences
sort file.txt | uniq -c | sort -rn        # Sorted by frequency

# Extract columns
awk '{print $1, $3}' file.txt            # Print columns 1 and 3
cut -d',' -f2,5 csv.csv                  # CSV column extraction

# Replace
sed 's/old/new/g' file.txt               # Replace all occurrences
sed -i 's/foo/bar/g' file.txt            # In-place replace

# Chain commands together
cat access.log | awk '{print $7}' | sort | uniq -c | sort -rn | head -20
# Top 20 most requested URLs

# tar.gz
tar -czvf archive.tar.gz folder/          # Create
tar -xzvf archive.tar.gz                  # Extract
tar -tzvf archive.tar.gz                  # List contents

# zip
zip -r archive.zip folder/               # Create
unzip archive.zip                         # Extract

# Quick extract anything
extract() {
  if [ -f $1 ]; then
    case $1 in *.tar.bz2) tar xjf $1 ;;
      *.tar.gz) tar xzf $1 ;;
      *.bz2) bunzip2 $1 ;;
      *.rar) unrar x $1 ;;
      *.gz) gunzip $1 ;;
      *.tar) tar xf $1 ;;
      *.tbz2) tar xjf $1 ;;
      *.tgz) tar xzf $1 ;;
      *.zip) unzip $1 ;;
      *) echo "Cannot extract '$1'" ;;
    esac
  fi
}

# Who am I?
whoami                                    # Current user
id                                        # User ID and groups
who                                       # Logged-in users
w                                         # Who's doing what

# Permissions
ls -la                                    # Detailed listing with permissions
chmod +x script.sh                        # Make executable
chmod 644 file.txt                        # rw-r--r--
chmod 755 script.sh                       # rwxr-xr-x
chown user:group file.txt                 # Change owner

# Sudo without password for specific command (be careful!)
sudo visudo → add: username ALL=(ALL) NOPASSWD: /usr/bin/systemctl restart nginx

uname -a                                  # Full system info
uname -m                                  # Architecture (x86_64/arm64)
cat /etc/os-release                      # OS version
uptime                                    # How long system has been running
lscpu                                     # CPU info
lsblk                                     # Block devices (disks)
free -h                                   # Memory
ip addr                                   # Network interfaces
systemctl status nginx                    # Service status
journalctl -u nginx -f                    # Follow service logs

# Deploy new code
cd /app && git pull origin main && npm run build && pm2 restart app

# Check what's eating disk
du -sh /* 2>/dev/null | sort -hr | head -10

# Quick backup
tar -czvf backup-$(date +%Y%m%d).tar.gz important_folder/

# Monitor a deploy
pm2 logs app --lines 50

# Fix permissions after deploy
chown -R www-data:www-data /app/public
chmod -R 755 /app/public

# Quick port check
ss -tlnp | grep -E '(3000|8080|443)'

# Find and delete old logs (>30 days)
find /var/log/app -name "*.log" -mtime +30 -delete