Essential Linux Commands for Cyber Security

Introduction

• Focus on essential Linux commands and flags.
• Important for ethical hacking and cybersecurity.
• Mastering these commands is crucial before advanced tools like Metasploit, nmap, etc.

Navigating the File System

Using Terminal

• Preferred method over GUI for navigating Linux file system.
• Open terminal to start.

Basic Commands

ls Command

• ls: Lists directory contents.
• Flags:
  • -l: Long listing format.
    • Displays permissions, number of links, owner, group, size, and date modified.
  • -a: Shows hidden files (those starting with .).
  • -t: Sorts by modification time, newest first.
  • -h: Human-readable file sizes.
  • Combining Flags: ls -lath for all combined.

cd Command

• cd: Change directory.
• Shortcuts:
  • Tab Completion: Auto-completes directory names.
  • cd -: Returns to the previous directory.
  • cd ..: Moves up one directory level.
  • cd: Returns to home directory.
  • pwd: Print working directory.

Manipulating Files and Directories

Creating Files and Directories

• touch: Creates empty files (e.g. touch file1 file2).
• mkdir: Makes directories (e.g. mkdir dir1).
• mkdir -p: Creates nested directories.
• Assigning Permissions: mkdir -m 777 dir sets full permissions.

Copying Files and Directories

• cp: Copy files (e.g. cp file1 file2).
• cp -r: Copy directories recursively.

Removing Files and Directories

• rm: Remove files (e.g. rm file1).
• rm -r: Remove directories recursively.
• rm -rf: Force remove files/directories (use with caution).

Moving and Renaming Files

• mv: Move or rename files (e.g. mv file1 newlocation).

Disk Usage and Space

Checking Disk Usage

• du: Disk usage of files and directories.
• Flags:
  • -h: Human-readable format.
  • -s: Summary of total usage.

File Permissions and Ownership

Modifying Permissions

• chmod: Change permissions (e.g. chmod g+rw file).
• Symbols: u (user), g (group), o (others), a (all).
• Numeric Mode: chmod 777 file gives full permissions.

Changing Ownership

• chown: Change file ownership (e.g. chown user:group file).

Viewing File Contents

cat Command

• cat: Concatenate and display file contents.
• Appending: cat file1 >> file2 appends file1 to file2.

tail Command

• tail: Displays last part of a file.
• Flags:
  • -n: Number of lines to display.
  • -f: Follow file updates (real-time).

head Command

• head: Displays first part of a file.
• Flags:
  • -n: Number of lines to display.

less and more

• less: View file contents page by page (better than more).
• more: Similar to less but with fewer features.

Text Editors

vi and nano

• vi: Powerful, complex text editor.
• nano: User-friendly, easy-to-use text editor.
• Basic Commands: Insert, save, quit, etc.

Process Management

Viewing Processes

• ps: Display current processes.
• ps aux: Detailed process listing.
• grep: Filter processes (e.g. ps aux | grep processname).

top Command

• top: Real-time process monitoring.
• htop: Enhanced version of top.

Killing Processes

• kill: Terminate process by ID (e.g. kill 1234).
• kill -9: Force kill (use with caution).

Background and Foreground Processes

• Background: command & to run in background.
• jobs: List background jobs.
• fg: Bring background job to foreground.

Networking Commands

Checking Network Configuration

• ifconfig: Network interface configuration (deprecated).
• ip: Newer command replacing ifconfig (e.g. ip addr).

Checking Routes

• ip route: Show routing table.

SSH and SCP

• ssh: Securely connect to remote machines.
• scp: Securely copy files between machines.

Viewing Network Connections

• netstat: Network statistics (deprecated).
• ss: Newer command showing socket statistics.

Finding Files

find Command

• find: Search for files (e.g. find /home -name '*.txt').
• grep: Search text within files.

Archiving and Compression

tar and gzip

• tar: Archive files into a tarball (e.g. tar -czf archive.tar.gz dir).
• gzip: Compress files (e.g. gzip file).
• Uncompress: gunzip for .gz files, tar -xzf for tarballs.

User Management

Adding and Deleting Users

• useradd: Add a new user (e.g. useradd username).
• userdel: Delete a user (e.g. userdel username).

Adding and Deleting Groups

• groupadd: Add a new group (e.g. groupadd groupname).
• groupdel: Delete a group (e.g. groupdel groupname).

Conclusion

• Importance of mastering basic Linux commands.
• Foundation for advanced cybersecurity tools and techniques.
• Encouragement to practice and utilize these commands efficiently.