Essential Linux Commands for Cybersecurity

Introduction

• Focus: Most essential Linux commands and their special flags
• Goal: Master these commands before advancing to tools like Metasploit, nmap, Hydra, etc.

Navigating the File System with ls

• ls: Lists directory contents (similar to dir in Windows)
• Flags:
  • -l: Long listing, provides detailed information
  • -a: Shows hidden files
  • -t: Sort by modification time
  • -h: Human-readable file sizes
  • Combine flags: ls -lath
• Recursion:
  • -R: Recursively list subdirectories

Changing Directories with cd

• cd: Change directory
  • Usage:
    • cd [directory]: Navigate to a directory
    • Tab completion
    • cd -: Switch to previous directory
    • cd ..: Move up one directory level
    • cd: Go to home directory
• pwd: Print working directory

Creating and Managing Files and Directories

• touch: Create empty files
  • Example: touch file1 file2 file3
• mkdir: Create directories
  • Example: mkdir dir1 dir2
  • Recursive creation: mkdir -p parent/child/grandchild
  • Setting permissions: mkdir -m 777 dir (full rights, not recommended)
• cp: Copy files and directories
  • cp file1 file2: Copy file
  • cp -R dir1 dir2: Copy directory recursively
• rm: Remove files and directories
  • rm file: Remove file
  • rm -rf dir: Recursively and forcibly remove directory
  • Wildcards: rm *.txt
• mv: Move or rename files
  • mv oldname newname: Rename file
  • mv file1 dir/: Move file to directory

Disk Usage with du

• du: Disk usage
  • du -h: Human-readable format
  • du -sh: Summary of directory size

File Permissions and Ownership

• chmod: Change file permissions
  • Syntax: chmod [permissions] [file]
  • Example: chmod u+x file (add execute permission for owner)
• chown: Change file owner and group
  • Syntax: chown [owner]:[group] [file]
  • Example: chown user:group file

Viewing and Editing Files

• cat: Concatenate and display files
  • Example: cat file
  • Combine files: cat file1 file2 > newfile
  • Append to file: cat file >> existingfile
• tail: View end of file
  • tail file: Last 10 lines
  • tail -n 20 file: Last 20 lines
  • tail -f file: Follow updates to file
• head: View beginning of file
  • head file: First 10 lines
  • head -n 20 file: First 20 lines
• less: View file one page at a time
  • Navigation: Space to scroll, /search to find, q to quit
• nano: Simple text editor
  • nano file: Open file in nano
  • Basic commands shown at the bottom
• vi: Advanced text editor
  • vi file: Open file in vi
  • Modes: i to insert, esc to exit insert mode, :wq to save and quit

Process Management

• ps: Display process status
  • ps aux: Detailed view of all processes
• top: Dynamic view of system processes
  • Real-time updates, sortable by resource usage
  • q: Quit
• kill: Terminate processes
  • kill PID: Kill process by PID
  • kill -9 PID: Force kill
• jobs: List background jobs
  • fg %1: Bring job 1 to foreground

Networking Commands

• ifconfig: Network interfaces (deprecated)
• ip: Newer networking tool
  • ip a: Show all IP addresses
  • ip route show: Show routing table
  • Add route: ip route add [dest] via [gateway] dev [interface]
  • Add IP: ip addr add [IP]/[prefix] dev [interface]
  • Remove IP: ip addr del [IP]/[prefix] dev [interface]
• netstat: Network statistics (deprecated)
  • netstat -l: Show listening ports
• ss: Socket statistics
  • ss -t: Show TCP connections
  • ss -u: Show UDP connections
  • ss -p: Show process names
• ssh: Secure shell
  • ssh user@host: Connect to remote host
  • -p [port]: Specify port
• scp: Secure copy
  • scp sourcefile user@host:/path: Copy file to remote host
• rsync: Remote synchronization
  • rsync -av source dest: Sync directories

System Information

• uname -a: Display system information
• df: Disk free space
  • df -h: Human-readable
  • df -T: Show filesystem type

Finding Files

• find: Search for files
  • find /path -name filename: Search by name
  • find /path -size +100M: Search by size
  • find /path -mtime -7: Search by modification time
• grep: Search within files
  • grep 'pattern' file: Search for pattern
  • grep -r 'pattern' /path: Recursive search

Archiving and Compression

• tar: Archive files
  • tar czf archive.tar.gz files: Create compressed archive
  • tar xzf archive.tar.gz: Extract archive
  • Add to archive: tar rf archive.tar file
• gzip: Compress files
  • gzip file: Compress file
  • gunzip file.gz: Decompress file
  • gzip -l file.gz: List contents of gzip file

User Management

• useradd: Add user
  • useradd username: Create new user
  • useradd -m username: Create user with home directory
  • useradd -G groupname username: Add user to group
  • useradd -e YYYY-MM-DD username: Set account expiration date
• userdel: Delete user
  • userdel username: Delete user
  • userdel -r username: Delete user and home directory
• groupadd: Add group
  • groupadd groupname: Create new group
• groupdel: Delete group
  • groupdel groupname: Delete group

Conclusion

• Summary: Mastering these commands lays a solid foundation for more advanced cybersecurity tools and techniques.
• Next Steps: Explore advanced tools and applications like Metasploit, nmap, and Hydra. Check out additional videos on these topics.