Ubuntu & CLI Commands Reference

# View system information
uname -a                    # Kernel information
lsb_release -a              # Ubuntu version
cat /etc/os-release         # OS information
cat /proc/cpuinfo           # CPU information
cat /proc/meminfo           # Memory information
free -h                     # View memory usage with human-readable units
df -h                       # Disk usage
lsblk                       # List block devices
sudo lshw                   # Hardware information
inxi -F                     # System information (may need: sudo apt install inxi)

# Navigation
pwd                         # Print working directory
ls                          # List files
ls -la                      # List all files with details
cd directory                # Change directory
cd ..                       # Go up one directory
cd ~                        # Go to home directory
cd -                        # Go to previous directory
 
# File manipulation
touch file.txt              # Create empty file
mkdir directory             # Create directory
mkdir -p dir1/dir2/dir3     # Create nested directories
cp file.txt backup.txt      # Copy file
cp -r dir1 dir2             # Copy directory recursively
mv file.txt newname.txt     # Rename/move file
mv file.txt directory/      # Move file to directory
rm file.txt                 # Delete file
rm -i file.txt              # Delete with confirmation
rm -r directory             # Delete directory recursively
rm -rf directory            # Force delete directory
 
# File examination
cat file.txt                # Display file contents
less file.txt               # View file with pagination
head -n 10 file.txt         # Display first 10 lines
tail -n 10 file.txt         # Display last 10 lines
tail -f log.txt             # Display and follow file updates
grep "text" file.txt        # Search for text in file
find /path -name "*.txt"    # Find files with .txt extension

# User info
whoami                      # Show current username
id                          # Show user ID and groups
who                         # Show logged-in users
w                           # Show who is logged in and what they're doing
 
# User/group management
sudo adduser username       # Create new user (interactive)
sudo useradd username       # Create new user (non-interactive)
sudo userdel username       # Delete user
sudo passwd username        # Change user password
sudo usermod -aG group user # Add user to group
sudo groupadd groupname     # Create new group
sudo groupdel groupname     # Delete group

# View and modify
ls -l                       # List with permissions
chmod 755 file.txt          # Change file permissions (rwx for owner, rx for others)
chmod -R 755 directory      # Change permissions recursively
chmod u+x script.sh         # Add execute permission for user
chown user:group file.txt   # Change file owner and group
chown -R user:group dir     # Change ownership recursively
 
# Common permission numbers
# 777 - rwxrwxrwx - Everyone can read, write, execute
# 755 - rwxr-xr-x - Owner can read, write, execute; others can read, execute
# 644 - rw-r--r-- - Owner can read, write; others can read
# 700 - rwx------ - Owner can read, write, execute; others have no permissions

# APT commands
sudo apt update                     # Update package lists
sudo apt upgrade                    # Upgrade all installed packages
sudo apt dist-upgrade               # Smart upgrade (handles dependencies)
sudo apt full-upgrade               # Upgrade with removals if necessary
sudo apt install package            # Install package
sudo apt remove package             # Remove package
sudo apt purge package              # Remove package and configuration
sudo apt autoremove                 # Remove unused dependencies
apt search keyword                  # Search for packages
apt show package                    # Show package details
apt list --installed                # List installed packages
 
# Snap commands
snap list                           # List installed snaps
sudo snap install package           # Install snap
sudo snap refresh package           # Update snap
sudo snap remove package            # Remove snap
snap find keyword                   # Search for snaps
 
# .deb files
sudo dpkg -i package.deb            # Install .deb file
sudo apt install -f                 # Fix dependencies after dpkg

# View processes
ps                          # Show running processes
ps aux                      # Show all processes
top                         # Interactive process viewer
htop                        # Enhanced process viewer (may need: sudo apt install htop)
pgrep process_name          # Find process ID by name
 
# Process control
kill PID                    # Terminate process by ID
killall process_name        # Terminate processes by name
pkill process_name          # Pattern-kill processes
kill -9 PID                 # Force kill process
nice -n 10 command          # Run command with lower priority
renice +10 -p PID           # Change priority of running process

# Connectivity
ping google.com             # Test network connectivity
ping -c 4 google.com        # Ping 4 times only
wget url                    # Download file from web
curl url                    # Fetch URL content
curl -O url                 # Download file with original name
 
# Network information
ifconfig                    # Show network interfaces (deprecated)
ip addr                     # Show IP addresses
ip route                    # Show routing table
netstat -tuln               # Show listening ports
ss -tuln                    # Show listening ports (newer alternative)
hostname -I                 # Show IP addresses
dig domain.com              # DNS lookup
nslookup domain.com         # DNS lookup
whois domain.com            # Domain registration info
 
# Network configuration
sudo dhclient -r            # Release DHCP address
sudo dhclient               # Renew DHCP address
sudo ip link set eth0 up    # Bring interface up
sudo ip link set eth0 down  # Bring interface down

# SSH commands
ssh user@hostname           # Connect to remote host
ssh -p 2222 user@hostname   # Connect on specific port
ssh-keygen -t rsa           # Generate SSH key pair
ssh-copy-id user@hostname   # Copy SSH key to remote host
scp file.txt user@host:/path # Copy file to remote host
scp user@host:/path/file.txt . # Copy from remote to local
rsync -av dir/ user@host:/path # Sync directory to remote
 
# Screen and tmux for persistent sessions
screen                      # Start screen session
screen -r                   # Reattach to screen session
tmux                        # Start tmux session
tmux ls                     # List sessions
tmux attach -t 0            # Attach to session 0

# Text manipulation
grep pattern file.txt       # Search for pattern
grep -r pattern directory   # Recursive search
grep -i pattern file.txt    # Case-insensitive search
grep -v pattern file.txt    # Invert match (lines without pattern)
sed 's/old/new/g' file.txt  # Replace text
awk '{print $1}' file.txt   # Print first column
sort file.txt               # Sort lines
uniq file.txt               # Remove duplicate lines
wc -l file.txt              # Count lines
wc -w file.txt              # Count words
cut -d, -f1 file.csv        # Extract first column from CSV

# Systemd service management
systemctl status service    # Check service status
sudo systemctl start service # Start service
sudo systemctl stop service # Stop service
sudo systemctl restart service # Restart service
sudo systemctl enable service # Enable at boot
sudo systemctl disable service # Disable at boot
sudo systemctl list-units --type=service # List services
journalctl -u service       # View service logs

# Disk operations
sudo fdisk -l               # List disk partitions
sudo mkfs.ext4 /dev/sdX1    # Format partition as ext4
sudo mount /dev/sdX1 /mnt   # Mount filesystem
sudo umount /mnt            # Unmount filesystem
sudo blkid                  # List block device attributes
sudo e2fsck -f /dev/sdX1    # Check filesystem
sudo smartctl -a /dev/sda   # Disk health (needs smartmontools)
 
# Disk usage
du -sh directory            # Directory size (summarized, human-readable)
du -h --max-depth=1 /       # Size of top-level directories
ncdu                        # Interactive disk usage analyzer

# tar operations
tar -cvf archive.tar files/ # Create tar archive
tar -xvf archive.tar        # Extract tar archive
tar -czvf archive.tar.gz files/ # Create compressed tar archive
tar -xzvf archive.tar.gz    # Extract compressed tar archive
tar -cjvf archive.tar.bz2 files/ # Create bzip2 compressed archive
tar -xjvf archive.tar.bz2   # Extract bzip2 compressed archive
 
# Other compression tools
zip -r archive.zip directory # Create zip archive
unzip archive.zip           # Extract zip archive
gzip file.txt               # Compress file with gzip
gunzip file.txt.gz          # Decompress gzip file
bzip2 file.txt              # Compress file with bzip2
bunzip2 file.txt.bz2        # Decompress bzip2 file

# System monitoring
uptime                      # Show system uptime
free -m                     # Memory usage in MB
vmstat                      # Virtual memory statistics
iostat                      # I/O statistics
mpstat                      # CPU statistics
sar                         # System activity reporter (needs sysstat)
dmesg                       # Kernel ring buffer
 
# System maintenance
sudo apt clean              # Clean apt cache
sudo apt autoclean          # Remove outdated packages
sudo update-grub            # Update GRUB bootloader
sudo update-initramfs -u    # Update initramfs
sudo dpkg-reconfigure package # Reconfigure package

# Cron commands
crontab -l                  # List user's cron jobs
crontab -e                  # Edit user's cron jobs
sudo crontab -u user -l     # List another user's cron jobs
 
# Format: minute hour day-of-month month day-of-week command
# Example: 0 5 * * * /path/to/script.sh  # Run at 5am every day

# UFW (Uncomplicated Firewall)
sudo ufw status             # Check firewall status
sudo ufw enable             # Enable firewall
sudo ufw disable            # Disable firewall
sudo ufw allow 22           # Allow SSH port
sudo ufw deny 80            # Deny HTTP port
sudo ufw delete deny 80     # Remove rule
sudo ufw allow from 192.168.1.0/24 # Allow from subnet

Ctrl+C                      # Interrupt (kill) current process
Ctrl+Z                      # Suspend current process
Ctrl+D                      # Exit current shell
Ctrl+L                      # Clear the screen
Ctrl+A                      # Move to beginning of line
Ctrl+E                      # Move to end of line
Ctrl+U                      # Cut from cursor to beginning of line
Ctrl+K                      # Cut from cursor to end of line
Ctrl+W                      # Cut the word before the cursor
Ctrl+Y                      # Paste from the kill buffer
Ctrl+R                      # Search command history
Tab                         # Auto-complete commands/filenames
Up/Down arrows              # Navigate through command history

# Viewing logs
cat /var/log/syslog         # System logs
cat /var/log/auth.log       # Authentication logs
cat /var/log/kern.log       # Kernel logs
journalctl                  # View systemd journal logs
journalctl -f               # Follow journal logs
journalctl --since today    # Logs from today
journalctl -b               # Logs from current boot

# Advanced system utilities
strace command              # Trace system calls
ltrace command              # Trace library calls
lsof                        # List open files
lsof -i :80                 # Show process using port 80
sudo iotop                  # I/O monitoring (may need: sudo apt install iotop)
sudo powertop               # Power usage monitoring (may need: sudo apt install powertop)

#!/bin/bash                 # Shebang line
 
# Variables
NAME="Ubuntu"
echo $NAME
 
# Conditionals
if [ "$NAME" = "Ubuntu" ]; then
    echo "This is Ubuntu"
else
    echo "This is not Ubuntu"
fi
 
# Loops
for i in {1..5}; do
    echo $i
done
 
# Functions
hello() {
    echo "Hello, $1!"
}
hello "World"