Essential Linux Commands for Cybersecurity

Introduction

• Purpose: Cover essential Linux commands for ethical hacking and cybersecurity.
• Focus: Basic commands and flags to enhance capabilities.

Navigating the File System

Using the Terminal

• Navigate with Terminal: Preferred over file explorer.
• Open Terminal: Essential for command usage.

ls Command

• Basic Command: ls lists files and directories.
• Flags:
  • -l (long listing): Provides detailed info (links, rights, owner, group, size, date).
  • -a (all): Shows hidden files.
  • -t (time): Orders by modification date.
  • -h (human-readable): Displays file sizes in KB, MB, etc.
  • Combine Flags: ls -lath for comprehensive listing.

cd Command

• Change Directory: cd [directory_name]
• Tips:
  • cd -: Switches to the previous directory.
  • cd ..: Moves up one level.
  • cd /path/to/dir: Directly navigate to a directory.
  • Tab Completion: Use Tab for auto-complete directory names.
  • Home Directory: cd ~ or just cd.

PWD Command

• Print Working Directory: pwd shows the current directory.

File and Directory Management

touch Command

• Create Files: touch file1 file2 ...

mkdir Command

• Create Directories: mkdir dir1 dir2 ...
• Flags:
  • -p: Creates parent directories as needed.
  • -m: Sets permissions (e.g., mkdir -m 777 dir).

cp Command

• Copy Files: cp source destination
• Copy Directories: cp -r source_dir destination_dir

rm Command

• Remove Files: rm file
• Remove Directories: rm -r dir
• Force Removal: rm -rf dir

mv Command

• Move/Rename Files: mv old_name new_name or mv file /new/path

Disk Usage

du Command

• Disk Usage: du [options] [dir]
• Flags:
  • -h: Human-readable sizes.
  • -s: Summarize total size.

Permissions and Ownership

chmod Command

• Change Permissions: chmod [permissions] file/dir
• Examples:
  • chmod 777 file: Full permissions.
  • chmod u+x file: Adds execute permission to the user.

chown Command

• Change Ownership: chown user:group file/dir
• Examples:
  • chown root:users file
  • chown user file

Viewing Files

cat Command

• View File Contents: cat file
• Combine Files: cat file1 file2 > combined_file
• Append Files: cat file >> existing_file

tail Command

• View End of File: tail file
• Flags:
  • -n [number]: Number of lines to show.
  • -f: Follow file updates.

head Command

• View Beginning of File: head file
• Flags:
  • -n [number]: Number of lines to show.

less & more Commands

• Paged Viewing: less file or more file
• Navigation: Use space to scroll.
• Search: /pattern in less

Text Editors

vi and nano

• vi: Advanced text editor (insert mode, command mode).
• nano: User-friendly text editor.

Process Management

ps Command

• View Processes: ps aux for detailed list.
• Flags:
  • aux: All processes with details.

top Command

• Real-Time Process Viewer: top
• User-Specific: top -u username

kill Command

• Terminate Processes: kill PID
• Force Terminate: kill -9 PID

Background Processes

• Start in Background: command &
• List Jobs: jobs
• Foreground: fg %job_number

Networking Commands

ifconfig and ip

• View Network Info: ifconfig or ip addr
• Default Gateway: ip route
• Add IP: ip addr add 192.168.1.1/24 dev eth0
• Remove IP: ip addr del 192.168.1.1/24 dev eth0

netstat and ss

• Network Statistics: netstat -l or ss -t

ssh and scp

• Secure Shell: ssh user@host
• Secure Copy: scp source user@host:/path

Checking System Info

uname Command

• System Info: uname -a

df Command

• Disk Free Space: df -h

Searching Files

find Command

• Search Files: find /path -name "pattern"
• By Size: find /path -size +1M
• By Time: find /path -mtime -30

grep Command

• Search in Files: grep "pattern" file

Archiving and Compression

tar Command

• Create Archive: tar czf archive.tar.gz files
• Extract Archive: tar xzf archive.tar.gz
• Add to Archive: tar rf archive.tar file

gzip Command

• Compress File: gzip file
• Decompress File: gunzip file.gz
• List Contents: gzip -l archive.tar.gz

User Management

useradd and userdel

• Add User: useradd username
• Delete User: userdel username

groupadd and groupdel

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

Conclusion

• Essentials Covered: Commands to navigate, manage files, processes, networking, and users.
• Further Learning: Practice and explore more advanced tools and commands.