Ubuntu CLI Handbook

1pwd                         # Print current working directory
2cd /path/to/dir             # Change directory
3cd ~                        # Go to home directory
4cd -                        # Go to previous directory
5cd ..                       # Go up one level
6pushd /path                 # Push directory onto stack and cd
7popd                        # Pop directory from stack and cd back

1ls                          # List files
2ls -la                      # List all files (including hidden) with details
3ls -lh                      # Human-readable file sizes
4ls -lt                      # Sort by modification time (newest first)
5ls -lS                      # Sort by size (largest first)
6ls -R                       # List recursively
7ls -i                       # Show inode numbers
8tree                        # Show directory tree (install: sudo apt install tree)
9tree -L 2                   # Limit tree depth to 2 levels

1find . -name "*.log"                  # Find files by name
2find . -iname "*.txt"                 # Case-insensitive search
3find / -type f -size +100M            # Files larger than 100 MB
4find . -type f -mtime -7              # Modified in last 7 days
5find . -type f -empty                 # Find empty files
6find . -type f -ls                    # Detailed listing of found files
7find . -name "*.tmp" -delete          # Find and delete
8locate filename                       # Fast search (uses index, run sudo updatedb first)
9which command                         # Show full path of a command
10whereis command                       # Locate binary, source, man page
11type command                          # Show how a command would be interpreted

1touch file.txt              # Create empty file / update timestamp
2mkdir dirname               # Create directory
3mkdir -p path/to/nested     # Create nested directories
4cp file.txt copy.txt        # Copy file
5cp -r dir/ dir_copy/        # Copy directory recursively
6mv old.txt new.txt          # Rename / move file
7rm file.txt                 # Delete file
8rm -rf directory/           # Delete directory recursively (use with caution!)
9rmdir empty_dir             # Remove empty directory only

1ln file hardlink            # Create hard link
2ln -s /path/to/file symlink # Create symbolic (soft) link
3readlink -f symlink         # Resolve full path of a symlink

1cat file.txt                # Print entire file
2less file.txt               # Scrollable viewer (q to quit)
3head -n 20 file.txt         # First 20 lines
4tail -n 20 file.txt         # Last 20 lines
5tail -f /var/log/syslog     # Follow file in real-time (great for logs)
6wc -l file.txt              # Count lines
7wc -w file.txt              # Count words
8diff file1 file2            # Compare two files
9stat file.txt               # Detailed file metadata
10file unknown_file           # Detect file type

1tar -czf archive.tar.gz dir/       # Create gzipped tar
2tar -xzf archive.tar.gz            # Extract gzipped tar
3tar -xzf archive.tar.gz -C /dest/  # Extract to specific directory
4tar -tf archive.tar.gz              # List contents without extracting
5zip -r archive.zip dir/            # Create zip
6unzip archive.zip                  # Extract zip
7gzip file                          # Compress (replaces original)
8gunzip file.gz                     # Decompress

1ls -la                       # View permissions
2stat -c '%A %a %n' file.txt # Octal + symbolic permissions
3getfacl file.txt             # View Access Control Lists

1chmod 755 file.txt           # rwxr-xr-x
2chmod 644 file.txt           # rw-r--r--
3chmod +x script.sh           # Add execute permission
4chmod -R 755 directory/      # Recursive permission change

1chown user file.txt              # Change owner
2chown user:group file.txt        # Change owner and group
3chown -R user:group directory/   # Recursive ownership change

1setfacl -m u:username:rwx file   # Grant user specific access
2getfacl -R /some/path > perms.txt  # Backup ACLs
3setfacl --restore=perms.txt        # Restore ACLs

1grep "pattern" file.txt          # Search for pattern
2grep -i "pattern" file.txt      # Case-insensitive
3grep -r "pattern" /path/        # Recursive search
4grep -n "pattern" file.txt      # Show line numbers
5grep -c "pattern" file.txt      # Count matches
6grep -v "pattern" file.txt      # Invert match (lines NOT matching)
7grep -l "pattern" *.log         # List filenames with matches
8grep -E "foo|bar" file.txt      # Extended regex (egrep)

1sed 's/old/new/' file.txt          # Replace first occurrence per line
2sed 's/old/new/g' file.txt         # Replace all occurrences
3sed -i 's/old/new/g' file.txt      # In-place edit
4sed -n '10,20p' file.txt           # Print lines 10-20
5sed '/pattern/d' file.txt          # Delete lines matching pattern

1awk '{print $1}' file.txt           # Print first column
2awk '{print $1, $3}' file.txt       # Print 1st and 3rd columns
3awk -F: '{print $1}' /etc/passwd    # Use : as delimiter
4awk '{x += $3} END {print x}' file  # Sum values in column 3
5awk 'NR==5,NR==10' file.txt         # Print lines 5 to 10

1sort file.txt                # Sort lines alphabetically
2sort -n file.txt             # Sort numerically
3sort -u file.txt             # Sort and remove duplicates
4uniq                         # Remove adjacent duplicates (use with sort)
5cut -d: -f1 /etc/passwd      # Cut fields by delimiter
6tr 'a-z' 'A-Z' < file.txt   # Translate characters (lowercase → uppercase)
7tee output.txt               # Read stdin, write to file AND stdout
8xargs                        # Build commands from stdin

1whoami                           # Current username
2id                               # Current user UID, GID, groups
3id username                      # Info about specific user
4sudo adduser username            # Create new user (interactive)
5sudo useradd username            # Create user (non-interactive)
6sudo passwd username             # Set/change password
7sudo deluser username            # Delete user
8sudo deluser --remove-home user  # Delete user + home directory
9su - username                    # Switch to another user
10sudo -i                          # Open root shell

1groups                           # List groups for current user
2groups username                  # List groups for a user
3sudo addgroup groupname          # Create group
4sudo adduser username groupname  # Add user to group
5sudo deluser username groupname  # Remove user from group
6sudo usermod -aG group username  # Append user to group (keeps existing)

1cat /etc/passwd                  # All user accounts
2cat /etc/group                   # All groups
3cat /etc/shadow                  # Password hashes (root only)
4cat /etc/sudoers                 # Sudoers config (edit with visudo!)

1ps aux                       # All running processes
2ps aux | grep nginx          # Find specific process
3top                          # Real-time process monitor
4htop                         # Better interactive process monitor (install: sudo apt install htop)
5pgrep -a nginx               # Find PID by name
6pidof nginx                  # Get PID of a running program

1kill PID                     # Terminate process (SIGTERM)
2kill -9 PID                  # Force kill (SIGKILL)
3pkill process_name           # Kill by name
4killall process_name         # Kill all instances by name

1command &                    # Run in background
2jobs                         # List background jobs
3fg %1                        # Bring job 1 to foreground
4bg %1                        # Resume job 1 in background
5nohup command &              # Run command immune to hangups
6disown %1                    # Detach job from terminal

1free -h                      # Memory usage
2uptime                       # System uptime and load averages
3vmstat 1                     # Virtual memory stats (every 1 sec)
4iostat 1                     # CPU and I/O stats
5lsof -p PID                 # Files opened by a process
6lsof -i :80                 # What process is using port 80

1df -h                        # Filesystem disk space usage
2df -i                        # Inode usage
3du -sh /path                 # Total size of a directory
4du -sh *                     # Size of each item in current dir
5du -h --max-depth=1          # One level deep summary
6ncdu /                       # Interactive disk usage browser (install: sudo apt install ncdu)

1lsblk                        # List block devices (disks, partitions)
2blkid                        # Show UUID and filesystem type
3fdisk -l                     # List partition tables
4mount                        # Show mounted filesystems
5mount /dev/sdb1 /mnt/data    # Mount a partition
6umount /mnt/data             # Unmount
7cat /etc/fstab               # Permanent mount configuration

1sudo apt update                    # Refresh package index
2sudo apt upgrade                   # Upgrade all installed packages
3sudo apt full-upgrade              # Upgrade with dependency changes
4sudo apt install package_name      # Install a package
5sudo apt remove package_name       # Remove a package (keep config)
6sudo apt purge package_name        # Remove package + config files
7sudo apt autoremove                # Remove unneeded dependencies
8sudo apt search keyword            # Search for packages
9sudo apt show package_name         # Show package details
10sudo apt list --installed          # List all installed packages
11sudo apt list --upgradable         # List upgradable packages

1dpkg -l                            # List all installed packages
2dpkg -l | grep package             # Check if a package is installed
3dpkg -S /path/to/file              # Which package owns this file?
4dpkg -i package.deb                # Install local .deb file
5dpkg --configure -a                # Configure partially installed packages
6dpkg --audit                       # List problematic packages

1cat /etc/apt/sources.list                 # Main repo config
2ls /etc/apt/sources.list.d/              # Additional repo configs
3sudo add-apt-repository ppa:name/ppa     # Add PPA
4sudo add-apt-repository --remove ppa:name/ppa  # Remove PPA

1snap list                          # List installed snaps
2sudo snap install package          # Install snap
3sudo snap remove package           # Remove snap
4sudo snap refresh                  # Update all snaps
5snap info package                  # Snap details

1ip addr show                 # Show IP addresses (modern)
2ip link show                 # Show network interfaces
3ip route show                # Show routing table / default gateway
4hostname -I                  # Quick way to get local IP
5ifconfig                     # Legacy IP info (net-tools)

1ping -c 4 google.com         # Ping with 4 packets
2traceroute google.com        # Trace route to host
3mtr google.com               # Combined ping + traceroute
4curl -I https://example.com  # Fetch HTTP headers
5wget https://example.com/file.tar.gz  # Download file

1dig example.com              # DNS lookup
2dig +short example.com       # Short DNS answer
3nslookup example.com         # Legacy DNS lookup
4host example.com             # Simple DNS lookup
5cat /etc/resolv.conf         # DNS resolver configuration
6resolvectl status            # systemd-resolved DNS status

1ss -tulnp                    # List listening ports (modern)
2ss -plat                     # All TCP connections with processes
3netstat -tulnp               # Legacy listening ports
4lsof -iTCP -sTCP:LISTEN -P -n   # Listening TCP processes
5nmap -sT localhost           # Port scan (install: sudo apt install nmap)

1sudo ufw status              # Show firewall status
2sudo ufw enable              # Enable firewall
3sudo ufw disable             # Disable firewall
4sudo ufw allow 22/tcp        # Allow SSH
5sudo ufw allow 80/tcp        # Allow HTTP
6sudo ufw allow 443/tcp       # Allow HTTPS
7sudo ufw deny 3306           # Block MySQL port
8sudo ufw delete allow 80/tcp # Remove a rule
9sudo ufw logging on          # Enable logging
10sudo ufw reset               # Reset all rules

1ls /etc/netplan/              # Netplan config files
2cat /etc/netplan/*.yaml       # View network config
3sudo netplan apply            # Apply network changes
4sudo netplan try              # Test config (auto-reverts on failure)

1sudo systemctl start service        # Start a service
2sudo systemctl stop service         # Stop a service
3sudo systemctl restart service      # Restart a service
4sudo systemctl reload service       # Reload config without restart
5sudo systemctl status service       # Check service status
6sudo systemctl enable service       # Enable on boot
7sudo systemctl disable service      # Disable on boot
8sudo systemctl is-active service    # Check if active
9sudo systemctl is-enabled service   # Check if enabled on boot

1systemctl list-units --type=service             # List running services
2systemctl list-units --type=service --all        # List all services
3systemctl list-unit-files                        # List unit files (enabled/disabled)
4systemctl cat service                            # Show unit file content
5systemctl show service                           # Show all properties

1sudo systemctl daemon-reload     # Reload unit files after changes
2sudo systemctl poweroff          # Shutdown
3sudo systemctl reboot            # Reboot
4sudo systemctl suspend           # Suspend
5sudo systemctl hibernate         # Hibernate

1systemctl list-timers            # List active timers
2systemctl status snap.certbot.renew.timer  # Timer status example

1journalctl                           # All logs
2journalctl -u nginx                  # Logs for specific service
3journalctl -u nginx --since today    # Since today
4journalctl -u nginx --since "1 hour ago"
5journalctl -f                        # Follow logs in real-time
6journalctl -p err                    # Only errors
7journalctl -p warning                # Warnings and above
8journalctl --disk-usage              # Log storage size
9journalctl -b                        # Logs from current boot
10journalctl -b -1                     # Logs from previous boot
11journalctl --list-boots              # List all boot sessions

1# Most logs are in /var/log/
2ls /var/log/
3
4# Key log files:
5cat /var/log/syslog              # General system log
6cat /var/log/auth.log            # Authentication & sudo logs
7cat /var/log/kern.log            # Kernel messages
8cat /var/log/dpkg.log            # Package manager log
9cat /var/log/apt/history.log     # APT install history
10cat /var/log/boot.log            # Boot messages
11cat /var/log/ufw.log             # Firewall log (if UFW enabled)
12
13# Nginx / Apache logs:
14cat /var/log/nginx/access.log
15cat /var/log/nginx/error.log
16cat /var/log/apache2/access.log
17cat /var/log/apache2/error.log
18
19# MySQL / MariaDB:
20cat /var/log/mysql/error.log
21
22# Follow logs in real-time:
23tail -f /var/log/syslog

1dmesg                                # All kernel messages
2dmesg | tail -20                     # Last 20 kernel messages
3dmesg -T                             # Human-readable timestamps
4dmesg --level=err                    # Only errors
5dmesg -w                             # Follow in real-time

1ssh user@host                    # Connect to remote host
2ssh -p 2222 user@host            # Custom port
3ssh -i ~/.ssh/key.pem user@host  # Specify private key
4ssh -L 8080:localhost:80 user@host  # Local port forwarding
5ssh -J jumphost user@target      # Jump through bastion host

1ssh-keygen -t ed25519 -C "[email protected]"  # Generate key pair
2ssh-copy-id user@host                          # Copy public key to server
3cat ~/.ssh/authorized_keys                     # View authorized keys
4eval "$(ssh-agent -s)" && ssh-add ~/.ssh/key   # Start agent & add key

1cat ~/.ssh/config    # Per-user SSH config

1Host myserver
2    HostName 192.168.1.100
3    User admin
4    Port 22
5    IdentityFile ~/.ssh/mykey

1crontab -e                   # Edit current user's crontab
2crontab -l                   # List current crontab
3crontab -r                   # Remove current crontab
4sudo crontab -u user -e      # Edit another user's crontab

1# ┌───────────── minute (0–59)
2# │ ┌───────────── hour (0–23)
3# │ │ ┌───────────── day of month (1–31)
4# │ │ │ ┌───────────── month (1–12)
5# │ │ │ │ ┌───────────── day of week (0–7, 0 & 7 = Sunday)
6# │ │ │ │ │
7# * * * * * command_to_run
8
9# Examples:
100 2 * * *   /usr/local/bin/backup.sh      # Daily at 2:00 AM
11*/15 * * * * /usr/bin/check-health.sh      # Every 15 minutes
120 0 * * 0   /usr/local/bin/weekly.sh       # Weekly on Sunday midnight
13@reboot     /usr/local/bin/on-startup.sh   # Run at boot

1ls /etc/cron.d/          # Custom cron files
2ls /etc/cron.daily/      # Runs daily
3ls /etc/cron.hourly/     # Runs hourly
4ls /etc/cron.weekly/     # Runs weekly
5ls /etc/cron.monthly/    # Runs monthly

1uname -a                     # Kernel & OS info
2lsb_release -a               # Ubuntu version details
3cat /etc/os-release           # OS release info
4hostnamectl                   # Hostname and OS details
5arch                          # CPU architecture
6lscpu                         # CPU info
7lsmem                         # Memory info
8lspci                         # PCI devices
9lsusb                         # USB devices
10lshw -short                   # Full hardware summary
11dmidecode -t memory           # Detailed RAM info (root)

1free -h                       # Memory usage
2uptime                        # Uptime & load
3cat /proc/cpuinfo             # CPU details
4cat /proc/meminfo             # Memory details
5nproc                         # Number of CPU cores

1date                          # Current date/time
2timedatectl                   # Timezone & NTP status
3sudo timedatectl set-timezone America/New_York  # Set timezone

1env                           # List all environment variables
2echo $PATH                    # Print specific variable
3echo $HOME                    # Home directory
4export VAR="value"            # Set variable for current session
5printenv VAR                  # Print variable value

1# For current user — add to ~/.bashrc:
2echo 'export MY_VAR="value"' >> ~/.bashrc
3source ~/.bashrc
4
5# System-wide — add to /etc/environment:
6sudo nano /etc/environment
7# Add: MY_VAR="value"

1history                       # Show command history
2history | grep ssh            # Search history
3!!                            # Repeat last command
4!$                            # Last argument of previous command
5ctrl+r                        # Reverse search in history

1command > file.txt            # Redirect stdout to file (overwrite)
2command >> file.txt           # Append stdout to file
3command 2> error.log          # Redirect stderr
4command &> all.log            # Redirect both stdout and stderr
5command1 | command2           # Pipe stdout to next command
6command | tee file.txt        # Pipe and save to file simultaneously

1ctrl+c                        # Cancel current command
2ctrl+z                        # Suspend current command
3ctrl+d                        # Logout / end input
4ctrl+l                        # Clear screen
5ctrl+a                        # Move cursor to beginning of line
6ctrl+e                        # Move cursor to end of line
7ctrl+w                        # Delete word before cursor
8ctrl+u                        # Delete from cursor to beginning of line
9ctrl+k                        # Delete from cursor to end of line
10tab                           # Auto-complete

1alias ll='ls -la'                     # Create an alias
2sudo !!                               # Run last command as sudo
3watch -n 5 'df -h'                    # Repeat command every 5 seconds
4time command                          # Measure execution time
5yes | command                         # Auto-confirm prompts
6command1 && command2                   # Run command2 only if command1 succeeds
7command1 || command2                   # Run command2 only if command1 fails