Essential Linux Commands for Cyber Security

Introduction

• Essential Linux commands and flags for cyber security
• Importance of mastering basic commands before advanced tools like Metasploit, nmap, Hydra

Navigating the File System

Using Terminal over File Explorer

• Open terminal to navigate file system

ls Command

• Basic usage: ls similar to dir in Windows
• Flags for ls:
  • ls -l: Long listing (detailed file info)
  • ls -a: Show hidden files
  • ls -t: Sort by modification time
  • ls -h: Human-readable file sizes
  • Combine flags: ls -lath

Changing Directories with cd

• Basic usage: cd directory_name
• Tips:
  • Use Tab for auto-completion
  • cd -: Go back to the previous directory
  • cd ..: Move up one level
  • cd ~: Go to home directory
• Display current directory: pwd

Manipulating Files and Directories

Creating Files

• touch filename: Create a blank file
• Create multiple files: touch file1 file2 file3

Creating Directories

• mkdir directory_name: Create a single directory
• mkdir -p parent/child: Create nested directories
• Set permissions while creating: mkdir -m 777 directory_name

Copying Files and Directories

• Copy a file: cp source_file target_file
• Copy a directory: cp -r source_directory target_directory

Removing Files and Directories

• Remove a file: rm filename
• Remove a directory: rm -r directory_name
• WARNING: rm -rf / can delete the entire system

Moving and Renaming Files

• Move/Rename a file: mv source_file target_file
• Move multiple files: mv file1 file2 directory

Disk Usage and Filesystem

Disk Usage

• Check disk usage: du
• Human-readable: du -h
• Summary: du -sh

File Permissions and Ownership

Changing Permissions

• chmod ugo+rwx filename: Change permissions
• Numerical mode: chmod 777 filename
• Remove execute rights: chmod u-x filename

Changing Ownership

• Change owner: chown user filename
• Change group: chgrp group filename
• Change both owner and group: chown user:group filename

Viewing and Editing Files

Viewing Files

• cat filename: Display file content
• Combine files: cat file1 file2 > file3
• Append to a file: cat file1 >> file3

Tail and Head

• tail filename: Show last 10 lines
• head filename: Show first 10 lines
• Follow file updates: tail -f filename

Less and More

• less filename: View file one page at a time
• more filename: Similar to less but with fewer features

Text Editors

• nano filename: Easy-to-use text editor
• vi filename: Powerful but complex text editor

Process Management

Viewing Processes

• ps: Show current user's processes
• ps aux: Detailed view of all processes
• top: Real-time system statistics
• View user-specific processes: top -u username

Killing Processes

• kill PID: Terminate a process
• Forced kill: kill -9 PID
• Interrupt process: kill -2 PID

Background and Foreground Processes

• Send to background: command &
• View background jobs: jobs
• Bring to foreground: fg %job_number

Networking Commands

Viewing and Configuring Network

• ifconfig: View network interfaces (deprecated)
• ip a: View network interfaces (replacement)
• ip route: Show routing table
• Add route: ip route add subnet via gateway dev interface

Inspecting Network Connections

• netstat -l: View listening ports
• ss -t: View TCP connections
• ss -u: View UDP connections
• ss -p: View processes using sockets

SSH and File Transfer

• ssh user@host: Secure Shell connection
• scp source_file user@host:target_directory: Securely copy files
• rsync: Advanced file copy and synchronization

System Information

• uname -a: Display system information
• df -h: Show disk space usage (human-readable)

Searching Files

Find and Grep

• find /path -name filename: Search for files
• Search by size: find /path -size +1M
• Search by modification time: find /path -mtime -30
• grep pattern file: Search within files

Archiving and Compression

Tar and Gzip

• Create archive: tar cf archive.tar files
• Extract archive: tar xf archive.tar
• Compress file: gzip filename
• Decompress: gunzip filename.gz

User and Group Management

• Add user: useradd username
• Delete user: userdel username
• Add group: groupadd groupname
• Delete group: groupdel groupname

Conclusion

• Importance of mastering these commands for cyber security
• Encouragement to practice and explore additional resources