Essential Linux Commands for Cyber Security

Introduction

• Focus on essential Linux commands and flags.
• Target audience: aspiring ethical hackers and cybersecurity professionals.
• Importance of mastering these commands before advanced tools like Metasploit, nmap, etc.

Navigating the Linux File System

Using Terminal Over File Explorer

• Prefer terminal for navigation over GUI file explorer.

Basic Commands

ls Command

• Basic Usage: Lists contents of a directory.
• Flags:
  • ls -l: Long listing format with detailed information (links, ownership, size, date).
  • ls -a: Includes hidden files.
  • ls -t: Sorts by modification time.
  • ls -h: Human-readable file sizes.
  • Combined: ls -lath

cd Command

• Basic Usage: Change directory.
• Navigation Shortcuts:
  • cd -: Go back to the previous directory.
  • cd ..: Move up one directory level.
  • cd ~: Go to the home directory.
• Tab Completion: Using tab to auto-complete directory names.

pwd Command

• Usage: Print working directory.

Manipulating Files and Directories

Creating Files and Directories

• Create Files: touch file1 file2 file3
• Create Directories: mkdir dir1
• Create Nested Directories: mkdir -p parent/child/grandchild
• Permissions: mkdir -m 777 dir (sets full permissions)

Copying Files and Directories

• Copy Files: cp source_file destination_file
• Copy Directories: cp -r source_dir destination_dir

Removing Files and Directories

• Remove Files: rm file
• Remove Directories: rm -r dir
• Remove with Wildcards: rm test*

Moving and Renaming Files and Directories

• Move Files: mv source_file destination_file
• Rename Files: mv old_name new_name

Disk Usage and Space

du Command

• Basic Usage: Disk usage of directories.
• Flags:
  • du -h: Human-readable sizes.
  • du -s: Summarize total size.
• Example: du -sh *

Managing File Permissions

Understanding Permissions

• Symbols: r (read), w (write), x (execute).
• Groups: Owner, Group, Others.

Changing Permissions

• Command: chmod
• Adding/Removing Permissions: chmod u+x file (user execute), chmod g-w file (group write)
• Numeric Notation: chmod 755 file (sets rwxr-xr-x)

Changing Ownership

• Command: chown
• Change Owner: chown user file
• Change Group: chown :group file
• Change Both: chown user:group file

Viewing File Contents

cat Command

• Basic Usage: Display file contents.
• Combine Files: cat file1 file2 > combined_file
• Append Files: cat file3 >> combined_file

tail Command

• Basic Usage: View last 10 lines.
• Flags:
  • tail -n 15 file: Last 15 lines.
  • tail -f file: Follow updates in real-time.

head Command

• Basic Usage: View first 10 lines.
• Flags: head -n 15 file: First 15 lines.

less and more Commands

• Usage: Page through file contents.
• Search: Use /pattern in less to search.

Text Editors

vi and vim Editors

• Basic Usage: vi file
• Insert Mode: i to insert text.
• Save and Exit: :wq

nano Editor

• Basic Usage: nano file
• Ease of Use: Intuitive commands at the bottom.

Process Management

ps Command

• Basic Usage: List processes.
• Flags: ps aux for detailed view.

top Command

• Usage: Interactive process viewer.
• Filter by User: top -u username
• Monitor Specific Process: top -p PID

Killing Processes

• Command: kill PID
• Force Kill: kill -9 PID

Networking Commands

Viewing Network Configuration

• Commands: ifconfig, ip addr, ip route show
• Setting IP Address: ip addr add 192.168.1.10/24 dev eth0

Checking Routes

• Command: ip route

Connection and File Transfers

• SSH: ssh user@hostname
• Copy Files: scp source_file user@hostname:/path/to/destination
• Synchronize Files: rsync -avz source/ destination/

System Information

uname Command

• Flags: uname -a for detailed system info.

df Command

• Basic Usage: Disk free space.
• Human Readable: df -h

Searching and Finding Files

find Command

• Search by Name: find /path -name filename
• Search by Size: find /path -size +1M
• Search by Modification Time: find /path -mtime -30

grep Command

• Basic Usage: Search within files.
• Example: grep 'pattern' filename

Archiving and Compressing Files

tar Command

• Creating Archives: tar -cvf archive.tar files
• Extracting Archives: tar -xvf archive.tar
• With Compression: tar -czvf archive.tar.gz files

gzip Command

• Compress Files: gzip file
• Decompress Files: gunzip file.gz
• List Contents: gzip -l file.gz

User and Group Management

Adding and Deleting Users

• Add User: useradd username
• Add User with Home Directory: useradd -m username
• Delete User: userdel username

Adding and Deleting Groups

• Add Group: groupadd groupname
• Delete Group: groupdel groupname

Conclusion

• Recap of essential Linux commands crucial for cybersecurity professionals.
• Encouragement to practice and master these commands before moving to advanced tools.