uname -a                # Kernel info
hostname                # Hostname
whoami                  # Current user
uptime                  # System uptime
date                    # Current date/time
df -h                   # Disk usage
free -h                 # Memory usage
top                     # Process monitor
htop                    # Enhanced process monitor

ls -l                   # List files
ls -a                   # Show hidden files
cd /path/to/dir         # Change directory
pwd                     # Print working directory
mkdir newdir            # Create directory
rm file.txt             # Remove file
rm -r folder            # Remove directory recursively
cp file1 file2          # Copy file
mv old new              # Move/rename file
touch file.txt          # Create empty file
find . -name "*.sh"     # Find files by name

cat file.txt            # Show file content
less file.txt           # View file with paging
head -n 10 file.txt     # First 10 lines
tail -n 10 file.txt     # Last 10 lines
grep "text" file.txt    # Search in file
wc -l file.txt          # Line count
sort file.txt           # Sort lines
uniq file.txt           # Unique lines

chmod +x script.sh      # Make executable
chmod 644 file.txt      # Set permissions
chown user:group file   # Change owner
ls -l                   # Show permissions

tar -czvf archive.tar.gz folder/   # Compress
tar -xzvf archive.tar.gz           # Extract
zip file.zip file.txt              # Zip file
unzip file.zip                     # Unzip file
gzip file.txt                      # Compress to .gz
gunzip file.txt.gz                 # Decompress .gz

ping google.com                    # Test connectivity
curl https://example.com           # Fetch URL
wget https://example.com/file      # Download file
ifconfig                           # Network interfaces (deprecated)
ip addr                            # Network interfaces (modern)
netstat -tuln                      # List open ports
ss -tuln                           # List open ports (modern)

ps aux                             # List processes
kill -9 PID                        # Kill process
jobs                               # List background jobs
bg %1                              # Resume job in background
fg %1                              # Bring job to foreground
&                                  # Run in background

adduser newuser                    # Add user
passwd newuser                     # Set password
deluser olduser                    # Delete user
usermod -aG group user             # Add user to group
groups                             # Show user groups
id                                 # Show user info

crontab -e                         # Edit cron jobs
crontab -l                         # List cron jobs
at 18:00                           # Run command at specific time

history                            # Command history
alias ll='ls -l'                   # Create alias
man ls                             # Manual page
which python                       # Show command path
echo $PATH                         # Show