$ pwd # Print working directory cd ~ # Go to home directory cd - # Go to previous directory cd ../.. # Go up two levels ls # List files ls -la # List all files (including hidden) with details ls -lh # Human-readable file sizes ls -lt # Sort by modification time (newest first) tree # Visual directory tree tree -L 2 # Tree limited to 2 levels deep pushd /var/log # Push directory onto stack & cd into it popd # Pop directory off stack & return pwd # Print working directory cd ~ # Go to home directory cd - # Go to previous directory cd ../.. # Go up two levels ls # List files ls -la # List all files (including hidden) with details ls -lh # Human-readable file sizes ls -lt # Sort by modification time (newest first) tree # Visual directory tree tree -L 2 # Tree limited to 2 levels deep pushd /var/log # Push directory onto stack & cd into it popd # Pop directory off stack & return pwd # Print working directory cd ~ # Go to home directory cd - # Go to previous directory cd ../.. # Go up two levels ls # List files ls -la # List all files (including hidden) with details ls -lh # Human-readable file sizes ls -lt # Sort by modification time (newest first) tree # Visual directory tree tree -L 2 # Tree limited to 2 levels deep pushd /var/log # Push directory onto stack & cd into it popd # Pop directory off stack & return touch file.txt # Create empty file / -weight: 500;">update timestamp mkdir -p a/b/c # Create nested directories cp file.txt backup.txt # Copy file cp -r dir/ newdir/ # Copy directory recursively mv file.txt /tmp/ # Move file mv old.txt new.txt # Rename file rm file.txt # Delete file rm -rf dir/ # Force-delete directory recursively ln -s /path/to/file link # Create symbolic link find . -name "*.log" # Find files by name find . -mtime -7 # Files modified in last 7 days find . -size +100M # Files larger than 100MB find . -name "*.tmp" -delete # Find and delete locate filename # Fast file search (uses DB) touch file.txt # Create empty file / -weight: 500;">update timestamp mkdir -p a/b/c # Create nested directories cp file.txt backup.txt # Copy file cp -r dir/ newdir/ # Copy directory recursively mv file.txt /tmp/ # Move file mv old.txt new.txt # Rename file rm file.txt # Delete file rm -rf dir/ # Force-delete directory recursively ln -s /path/to/file link # Create symbolic link find . -name "*.log" # Find files by name find . -mtime -7 # Files modified in last 7 days find . -size +100M # Files larger than 100MB find . -name "*.tmp" -delete # Find and delete locate filename # Fast file search (uses DB) touch file.txt # Create empty file / -weight: 500;">update timestamp mkdir -p a/b/c # Create nested directories cp file.txt backup.txt # Copy file cp -r dir/ newdir/ # Copy directory recursively mv file.txt /tmp/ # Move file mv old.txt new.txt # Rename file rm file.txt # Delete file rm -rf dir/ # Force-delete directory recursively ln -s /path/to/file link # Create symbolic link find . -name "*.log" # Find files by name find . -mtime -7 # Files modified in last 7 days find . -size +100M # Files larger than 100MB find . -name "*.tmp" -delete # Find and delete locate filename # Fast file search (uses DB) cat file.txt # Print file to stdout cat -n file.txt # Print with line numbers less file.txt # Paginate file (q to quit) head -n 20 file.txt # First 20 lines tail -n 50 file.txt # Last 50 lines tail -f /var/log/syslog # Follow file in real-time wc -l file.txt # Count lines diff -u file1 file2 # Unified diff (patch-friendly) cat file.txt # Print file to stdout cat -n file.txt # Print with line numbers less file.txt # Paginate file (q to quit) head -n 20 file.txt # First 20 lines tail -n 50 file.txt # Last 50 lines tail -f /var/log/syslog # Follow file in real-time wc -l file.txt # Count lines diff -u file1 file2 # Unified diff (patch-friendly) cat file.txt # Print file to stdout cat -n file.txt # Print with line numbers less file.txt # Paginate file (q to quit) head -n 20 file.txt # First 20 lines tail -n 50 file.txt # Last 50 lines tail -f /var/log/syslog # Follow file in real-time wc -l file.txt # Count lines diff -u file1 file2 # Unified diff (patch-friendly) # grep grep "pattern" file.txt # Search for pattern grep -i "pattern" file.txt # Case-insensitive grep -r "pattern" ./dir/ # Recursive search grep -n "pattern" file.txt # Show line numbers grep -v "pattern" file.txt # Invert match (exclude) grep -c "pattern" file.txt # Count matching lines grep -A 3 "pattern" file.txt # 3 lines after match grep -E "pat1|pat2" file.txt # Extended regex (OR) # sed (Stream Editor) sed 's/old/new/' file.txt # Replace first occurrence per line sed 's/old/new/g' file.txt # Replace all occurrences sed -i 's/old/new/g' file.txt # Edit file in-place sed -n '5,10p' file.txt # Print lines 5-10 sed '/pattern/d' file.txt # Delete lines matching pattern # awk awk '{print $1}' file.txt # Print first column awk -F: '{print $1}' /etc/passwd # Use : as delimiter awk '{sum+=$1} END{print sum}' # Sum first column # Other text tools cut -d: -f1 /etc/passwd # Cut first field using : delimiter sort file.txt # Sort alphabetically sort -n numbers.txt # Sort numerically sort -u file.txt # Sort and -weight: 500;">remove duplicates uniq -c file.txt # Count duplicate lines tr 'a-z' 'A-Z' < file.txt # Translate lowercase to uppercase # grep grep "pattern" file.txt # Search for pattern grep -i "pattern" file.txt # Case-insensitive grep -r "pattern" ./dir/ # Recursive search grep -n "pattern" file.txt # Show line numbers grep -v "pattern" file.txt # Invert match (exclude) grep -c "pattern" file.txt # Count matching lines grep -A 3 "pattern" file.txt # 3 lines after match grep -E "pat1|pat2" file.txt # Extended regex (OR) # sed (Stream Editor) sed 's/old/new/' file.txt # Replace first occurrence per line sed 's/old/new/g' file.txt # Replace all occurrences sed -i 's/old/new/g' file.txt # Edit file in-place sed -n '5,10p' file.txt # Print lines 5-10 sed '/pattern/d' file.txt # Delete lines matching pattern # awk awk '{print $1}' file.txt # Print first column awk -F: '{print $1}' /etc/passwd # Use : as delimiter awk '{sum+=$1} END{print sum}' # Sum first column # Other text tools cut -d: -f1 /etc/passwd # Cut first field using : delimiter sort file.txt # Sort alphabetically sort -n numbers.txt # Sort numerically sort -u file.txt # Sort and -weight: 500;">remove duplicates uniq -c file.txt # Count duplicate lines tr 'a-z' 'A-Z' < file.txt # Translate lowercase to uppercase # grep grep "pattern" file.txt # Search for pattern grep -i "pattern" file.txt # Case-insensitive grep -r "pattern" ./dir/ # Recursive search grep -n "pattern" file.txt # Show line numbers grep -v "pattern" file.txt # Invert match (exclude) grep -c "pattern" file.txt # Count matching lines grep -A 3 "pattern" file.txt # 3 lines after match grep -E "pat1|pat2" file.txt # Extended regex (OR) # sed (Stream Editor) sed 's/old/new/' file.txt # Replace first occurrence per line sed 's/old/new/g' file.txt # Replace all occurrences sed -i 's/old/new/g' file.txt # Edit file in-place sed -n '5,10p' file.txt # Print lines 5-10 sed '/pattern/d' file.txt # Delete lines matching pattern # awk awk '{print $1}' file.txt # Print first column awk -F: '{print $1}' /etc/passwd # Use : as delimiter awk '{sum+=$1} END{print sum}' # Sum first column # Other text tools cut -d: -f1 /etc/passwd # Cut first field using : delimiter sort file.txt # Sort alphabetically sort -n numbers.txt # Sort numerically sort -u file.txt # Sort and -weight: 500;">remove duplicates uniq -c file.txt # Count duplicate lines tr 'a-z' 'A-Z' < file.txt # Translate lowercase to uppercase chmod 755 file # rwxr-xr-x chmod 644 file # rw-r--r-- chmod +x script.sh # Add execute permission chmod -R 755 dir/ # Apply recursively chown user:group file # Change owner and group chown -R user:group dir/ # Recursive ownership change umask 022 # Default mask (files 644, dirs 755) chmod 755 file # rwxr-xr-x chmod 644 file # rw-r--r-- chmod +x script.sh # Add execute permission chmod -R 755 dir/ # Apply recursively chown user:group file # Change owner and group chown -R user:group dir/ # Recursive ownership change umask 022 # Default mask (files 644, dirs 755) chmod 755 file # rwxr-xr-x chmod 644 file # rw-r--r-- chmod +x script.sh # Add execute permission chmod -R 755 dir/ # Apply recursively chown user:group file # Change owner and group chown -R user:group dir/ # Recursive ownership change umask 022 # Default mask (files 644, dirs 755) ps aux # All running processes ps aux | grep nginx # Find process by name pgrep nginx # Get PID by process name top # Interactive process viewer htop # Better interactive viewer kill PID # Send SIGTERM (graceful -weight: 500;">stop) kill -9 PID # Send SIGKILL (force -weight: 500;">stop) killall nginx # Kill all processes named nginx bg # Resume job in background fg # Bring background job to foreground jobs # List background jobs nohup command & # Run immune to hangups ps aux # All running processes ps aux | grep nginx # Find process by name pgrep nginx # Get PID by process name top # Interactive process viewer htop # Better interactive viewer kill PID # Send SIGTERM (graceful -weight: 500;">stop) kill -9 PID # Send SIGKILL (force -weight: 500;">stop) killall nginx # Kill all processes named nginx bg # Resume job in background fg # Bring background job to foreground jobs # List background jobs nohup command & # Run immune to hangups ps aux # All running processes ps aux | grep nginx # Find process by name pgrep nginx # Get PID by process name top # Interactive process viewer htop # Better interactive viewer kill PID # Send SIGTERM (graceful -weight: 500;">stop) kill -9 PID # Send SIGKILL (force -weight: 500;">stop) killall nginx # Kill all processes named nginx bg # Resume job in background fg # Bring background job to foreground jobs # List background jobs nohup command & # Run immune to hangups df -h # Disk space usage (human-readable) du -sh dir/ # Size of directory du -sh * | sort -h # All items sorted by size lsblk # List block devices as tree mount # Show all mounted filesystems stat file.txt # Detailed file metadata file mystery.bin # Identify file type df -h # Disk space usage (human-readable) du -sh dir/ # Size of directory du -sh * | sort -h # All items sorted by size lsblk # List block devices as tree mount # Show all mounted filesystems stat file.txt # Detailed file metadata file mystery.bin # Identify file type df -h # Disk space usage (human-readable) du -sh dir/ # Size of directory du -sh * | sort -h # All items sorted by size lsblk # List block devices as tree mount # Show all mounted filesystems stat file.txt # Detailed file metadata file mystery.bin # Identify file type # Connectivity ping -c 4 google.com # Ping exactly 4 times traceroute google.com # Trace network path -weight: 500;">curl https://example.com # Fetch URL content -weight: 500;">curl -I https://example.com # Fetch headers only -weight: 500;">curl -o file.zip URL # Download to file -weight: 500;">wget URL # Download file # Network info ip addr # Show IP addresses (modern) ip route # Show routing table ss -tuln # Show listening ports (modern) ss -tulnp # Include process names # DNS nslookup domain.com # DNS lookup dig domain.com # Detailed DNS lookup # SSH & Remote ssh user@host # Connect to host ssh -p 2222 user@host # Connect on custom port scp file.txt user@host:/path # Copy file to remote rsync -avz src/ user@host:dst/ # Sync files (fast, resumable) # Connectivity ping -c 4 google.com # Ping exactly 4 times traceroute google.com # Trace network path -weight: 500;">curl https://example.com # Fetch URL content -weight: 500;">curl -I https://example.com # Fetch headers only -weight: 500;">curl -o file.zip URL # Download to file -weight: 500;">wget URL # Download file # Network info ip addr # Show IP addresses (modern) ip route # Show routing table ss -tuln # Show listening ports (modern) ss -tulnp # Include process names # DNS nslookup domain.com # DNS lookup dig domain.com # Detailed DNS lookup # SSH & Remote ssh user@host # Connect to host ssh -p 2222 user@host # Connect on custom port scp file.txt user@host:/path # Copy file to remote rsync -avz src/ user@host:dst/ # Sync files (fast, resumable) # Connectivity ping -c 4 google.com # Ping exactly 4 times traceroute google.com # Trace network path -weight: 500;">curl https://example.com # Fetch URL content -weight: 500;">curl -I https://example.com # Fetch headers only -weight: 500;">curl -o file.zip URL # Download to file -weight: 500;">wget URL # Download file # Network info ip addr # Show IP addresses (modern) ip route # Show routing table ss -tuln # Show listening ports (modern) ss -tulnp # Include process names # DNS nslookup domain.com # DNS lookup dig domain.com # Detailed DNS lookup # SSH & Remote ssh user@host # Connect to host ssh -p 2222 user@host # Connect on custom port scp file.txt user@host:/path # Copy file to remote rsync -avz src/ user@host:dst/ # Sync files (fast, resumable) whoami # Current username id # User ID, group ID, groups useradd -m -s /bin/bash username # Create user with home dir usermod -aG -weight: 500;">docker username # Add user to group passwd username # Change user password groupadd developers # Create group -weight: 600;">sudo command # Run as root -weight: 600;">sudo -i # Interactive root shell whoami # Current username id # User ID, group ID, groups useradd -m -s /bin/bash username # Create user with home dir usermod -aG -weight: 500;">docker username # Add user to group passwd username # Change user password groupadd developers # Create group -weight: 600;">sudo command # Run as root -weight: 600;">sudo -i # Interactive root shell whoami # Current username id # User ID, group ID, groups useradd -m -s /bin/bash username # Create user with home dir usermod -aG -weight: 500;">docker username # Add user to group passwd username # Change user password groupadd developers # Create group -weight: 600;">sudo command # Run as root -weight: 600;">sudo -i # Interactive root shell -weight: 500;">apt -weight: 500;">update # Refresh package index -weight: 500;">apt -weight: 500;">upgrade # Upgrade all packages -weight: 500;">apt -weight: 500;">install nginx # Install package -weight: 500;">apt -weight: 500;">remove nginx # Remove package -weight: 500;">apt search keyword # Search for package -weight: 500;">apt -weight: 500;">update # Refresh package index -weight: 500;">apt -weight: 500;">upgrade # Upgrade all packages -weight: 500;">apt -weight: 500;">install nginx # Install package -weight: 500;">apt -weight: 500;">remove nginx # Remove package -weight: 500;">apt search keyword # Search for package -weight: 500;">apt -weight: 500;">update # Refresh package index -weight: 500;">apt -weight: 500;">upgrade # Upgrade all packages -weight: 500;">apt -weight: 500;">install nginx # Install package -weight: 500;">apt -weight: 500;">remove nginx # Remove package -weight: 500;">apt search keyword # Search for package -weight: 500;">dnf -weight: 500;">update # Update all packages -weight: 500;">dnf -weight: 500;">install nginx # Install package -weight: 500;">dnf -weight: 500;">remove nginx # Remove package -weight: 500;">dnf -weight: 500;">update # Update all packages -weight: 500;">dnf -weight: 500;">install nginx # Install package -weight: 500;">dnf -weight: 500;">remove nginx # Remove package -weight: 500;">dnf -weight: 500;">update # Update all packages -weight: 500;">dnf -weight: 500;">install nginx # Install package -weight: 500;">dnf -weight: 500;">remove nginx # Remove package tar -czvf archive.tar.gz dir/ # Create gzip-compressed tar tar -xzvf archive.tar.gz # Extract gzip tar tar -tf archive.tar # List contents without extracting tar -xzvf archive.tar.gz -C /tmp/ # Extract to specific directory zip -r archive.zip dir/ # Zip directory unzip archive.zip # Extract zip tar -czvf archive.tar.gz dir/ # Create gzip-compressed tar tar -xzvf archive.tar.gz # Extract gzip tar tar -tf archive.tar # List contents without extracting tar -xzvf archive.tar.gz -C /tmp/ # Extract to specific directory zip -r archive.zip dir/ # Zip directory unzip archive.zip # Extract zip tar -czvf archive.tar.gz dir/ # Create gzip-compressed tar tar -xzvf archive.tar.gz # Extract gzip tar tar -tf archive.tar # List contents without extracting tar -xzvf archive.tar.gz -C /tmp/ # Extract to specific directory zip -r archive.zip dir/ # Zip directory unzip archive.zip # Extract zip command > file.txt # Redirect stdout (overwrite) command >> file.txt # Redirect stdout (append) command 2> error.log # Redirect stderr command 2>&1 # Merge stderr into stdout command &> file.txt # Redirect both stdout + stderr command1 | command2 # Pipe stdout to next command tee file.txt # Write to file AND stdout # Useful pipe combos ps aux | grep nginx | grep -v grep find . -name "*.log" | xargs rm -f command > file.txt # Redirect stdout (overwrite) command >> file.txt # Redirect stdout (append) command 2> error.log # Redirect stderr command 2>&1 # Merge stderr into stdout command &> file.txt # Redirect both stdout + stderr command1 | command2 # Pipe stdout to next command tee file.txt # Write to file AND stdout # Useful pipe combos ps aux | grep nginx | grep -v grep find . -name "*.log" | xargs rm -f command > file.txt # Redirect stdout (overwrite) command >> file.txt # Redirect stdout (append) command 2> error.log # Redirect stderr command 2>&1 # Merge stderr into stdout command &> file.txt # Redirect both stdout + stderr command1 | command2 # Pipe stdout to next command tee file.txt # Write to file AND stdout # Useful pipe combos ps aux | grep nginx | grep -v grep find . -name "*.log" | xargs rm -f crontab -e # Edit crontab crontab -l # List crontab # Cron syntax: minute hour day month weekday command 0 2 * * * /backup.sh # Daily at 2:00 AM */15 * * * * /check.sh # Every 15 minutes 0 9 * * 1-5 /standup.sh # Weekdays at 9 AM crontab -e # Edit crontab crontab -l # List crontab # Cron syntax: minute hour day month weekday command 0 2 * * * /backup.sh # Daily at 2:00 AM */15 * * * * /check.sh # Every 15 minutes 0 9 * * 1-5 /standup.sh # Weekdays at 9 AM crontab -e # Edit crontab crontab -l # List crontab # Cron syntax: minute hour day month weekday command 0 2 * * * /backup.sh # Daily at 2:00 AM */15 * * * * /check.sh # Every 15 minutes 0 9 * * 1-5 /standup.sh # Weekdays at 9 AM ssh-keygen -t ed25519 -C "[email protected]" # Generate key (recommended) ssh-copy-id user@host # Copy public key to remote eval "$(ssh-agent -s)" # Start agent ssh-add ~/.ssh/id_ed25519 # Add key to agent ssh-keygen -t ed25519 -C "[email protected]" # Generate key (recommended) ssh-copy-id user@host # Copy public key to remote eval "$(ssh-agent -s)" # Start agent ssh-add ~/.ssh/id_ed25519 # Add key to agent ssh-keygen -t ed25519 -C "[email protected]" # Generate key (recommended) ssh-copy-id user@host # Copy public key to remote eval "$(ssh-agent -s)" # Start agent ssh-add ~/.ssh/id_ed25519 # Add key to agent -weight: 500;">systemctl -weight: 500;">start nginx # Start -weight: 500;">service -weight: 500;">systemctl -weight: 500;">stop nginx # Stop -weight: 500;">service -weight: 500;">systemctl -weight: 500;">restart nginx # Restart -weight: 500;">service -weight: 500;">systemctl -weight: 500;">enable nginx # Start on boot -weight: 500;">systemctl -weight: 500;">status nginx # Show -weight: 500;">service -weight: 500;">status journalctl -u nginx -f # Follow -weight: 500;">service logs -weight: 500;">systemctl -weight: 500;">start nginx # Start -weight: 500;">service -weight: 500;">systemctl -weight: 500;">stop nginx # Stop -weight: 500;">service -weight: 500;">systemctl -weight: 500;">restart nginx # Restart -weight: 500;">service -weight: 500;">systemctl -weight: 500;">enable nginx # Start on boot -weight: 500;">systemctl -weight: 500;">status nginx # Show -weight: 500;">service -weight: 500;">status journalctl -u nginx -f # Follow -weight: 500;">service logs -weight: 500;">systemctl -weight: 500;">start nginx # Start -weight: 500;">service -weight: 500;">systemctl -weight: 500;">stop nginx # Stop -weight: 500;">service -weight: 500;">systemctl -weight: 500;">restart nginx # Restart -weight: 500;">service -weight: 500;">systemctl -weight: 500;">enable nginx # Start on boot -weight: 500;">systemctl -weight: 500;">status nginx # Show -weight: 500;">service -weight: 500;">status journalctl -u nginx -f # Follow -weight: 500;">service logs - 7 (rwx) -- Read + Write + Execute - 6 (rw-) -- Read + Write - 5 (r-x) -- Read + Execute - 4 (r--) -- Read only - 0 (---) -- No permissions - SIGTERM (15) -- Graceful shutdown - SIGKILL (9) -- Force kill (can't catch) - SIGHUP (1) -- Reload config - SIGINT (2) -- Ctrl+C - Ctrl+C -- Kill current process - Ctrl+Z -- Suspend current process - Ctrl+D -- Exit shell / EOF - Ctrl+L -- Clear screen - Ctrl+R -- Search command history (reverse) - !! -- Repeat last command - -weight: 600;">sudo !! -- Re-run last command with -weight: 600;">sudo - rm -rf has no recycle bin -- it's permanent. Always double-check before running. - > overwrites, >> appends -- easy to lose data with the wrong one. - Spaces in filenames need quoting -- rm -rf My Documents removes "My" AND "Documents". - chmod -R 777 is almost always wrong -- massive security risk. - kill -9 should be a last resort -- data may not be flushed. Try kill -15 (SIGTERM) first. - -weight: 600;">sudo !! -- Run last command as -weight: 600;">sudo - touch file{1..5}.txt -- Create multiple files at once - cmd1 && cmd2 -- Run cmd2 only if cmd1 succeeds - python3 -m http.server 8080 -- Quick HTTP server in current directory - watch -n 2 df -h -- Watch a command run every 2 seconds