Essential Linux Commands for Ethical Hacking and Cybersecurity

Introduction

• Focus: Cover essential Linux commands and flags to enhance skills before advancing to tools like Metasploit, nmap, Hydra, etc.
• Importance: Mastering these basics is necessary for anyone serious about a cybersecurity career.

Navigating the Linux File System

Using the Terminal vs. File Explorer

• Terminal: Preferred method to navigate and manage files in Linux.

Commands

ls Command

• Basic Usage: Lists contents of a directory.
• Flags:
  • -l: Long listing format (details like permissions, owner, size, modification date).
  • -a: Includes hidden files (files starting with .).
  • -t: Sort by modification time (newest first).
  • -h: Human-readable file sizes.
  • Combine flags for more detailed output, e.g., ls -lath.
• Recursive Listing:
  • -R [directory]: Lists directory contents recursively.
  • Example: ls -R etc

cd Command

• Basic Usage: Change directory.
• Auto-Completion: Use tab for auto-complete directory names.
• Flags/Shortcuts:
  • cd -: Switch to the previous directory.
  • cd ..: Move up one directory level.
  • cd ~: Move to the home directory.

pwd Command

• Usage: Print working directory.
• Importance: Helps keep track of current directory.

Manipulating Files and Directories

Creating Files and Directories

touch Command

• Usage: Create empty files.
• Example: touch file1 file2 file3

mkdir Command

• Usage: Create directories.
• Flags:
  • -p: Create parent directories as needed.
  • -m [permissions]: Set permissions (e.g., 777) when creating.
• Examples:
  • mkdir -p dir1/dir2/dir3
  • mkdir -m 777 testdir

Copying Files and Directories

cp Command

• Basic Usage: Copy files.
• Flags:
  • -r: Copy directories recursively.
  • -f: Force overwrite.
• Examples:
  • cp file1 file2
  • cp -rf dir1 dir2

Removing Files and Directories

rm Command

• Basic Usage: Remove files.
• Flags:
  • -r: Remove directories recursively.
  • -f: Force removal.
• Examples:
  • rm file1
  • rm -rf directory

Moving and Renaming Files and Directories

mv Command

• Usage: Move or rename files and directories.
• Examples:
  • mv oldname newname
  • mv file1 /path/to/destination

Disk Usage and Space Management

du Command

• Usage: Disk usage of directories and files.
• Flags:
  • -h: Human-readable format.
  • -s: Summarize total.
• Example: du -sh /var/log

File Permissions and Ownership

Changing Permissions

chmod Command

• Usage: Change file and directory permissions.
• Flags:
  • u, g, o: User, group, other.
  • +, -: Add or remove permissions.
  • r, w, x: Read, write, execute.
• Examples:
  • chmod u+x filename
  • chmod 777 filename

Changing Ownership

chown Command

• Usage: Change file and directory ownership.
• Syntax: chown user:group filename
• Examples:
  • chown root:users file1
  • chown username: filename

Viewing and Editing Files

Viewing Files

cat Command

• Usage: Display file contents.
• Flags:
  • Concatenate and display multiple files.
  • Use > to redirect output.
  • Use >> to append to files.
• Example: cat file1 file2 > newfile

less and more Commands

• Usage: View large files page-by-page.
• Example: less filename, more filename

Editing Files

nano Command

• Usage: Simple text editor.
• Example: nano filename

vi Command

• Usage: Powerful text editor (steeper learning curve).
• Example: vi filename

Process Management

Viewing Processes

ps Command

• Usage: View process status.
• Flags:
  • aux: Detailed process list.
• Example: ps aux

top Command

• Usage: Real-time process monitoring.
• Flags:
  • -u [username]: Filter by user.
  • -p [PID]: Filter by process ID.
• Example: top -u root

Managing Processes

kill Command

• Usage: Terminate processes by ID.
• Flags:
  • -9 [PID]: Force kill.
• Example: kill -9 1234

jobs, fg, bg Commands

• Usage: Manage background and foreground jobs.
• Examples:
  • jobs: List background jobs.
  • fg [job]: Move job to foreground.
  • bg [job]: Move job to background.

Networking Commands

Checking Network Configuration

ifconfig and ip Commands

• Usage: Display network interfaces and IP addresses.
• Examples:
  • ifconfig
  • ip addr show
  • ip route show

Network Connections and Ports

netstat and ss Commands

• Usage: Display network connections, routing tables, etc.
• Flags:
  • -l: Listening ports.
  • -t: TCP connections.
  • -u: UDP connections.
• Examples:
  • netstat -ltu
  • ss -lt

Remote Connectivity

ssh Command

• Usage: Securely connect to remote systems.
• Examples:
  • ssh username@hostname
  • ssh -p [port] username@hostname

scp Command

• Usage: Secure copy files between hosts.
• Example: scp localfile user@remotehost:/path/to/destination

rsync Command

• Usage: Synchronize files and directories between hosts.
• Example: rsync -avz /source/ user@remote:/destination/

System Information

uname Command

• Usage: Display system information.
• Flags:
  • -a: All information.
• Example: uname -a

df Command

• Usage: Display disk space usage.
• Flags:
  • -h: Human-readable format.
  • -t: File system type.
• Example: df -hT

Searching for Files and Text

Finding Files

find Command

• Usage: Search for files in a directory hierarchy.
• Flags:
  • -name: Search by name.
  • -size: Search by file size.
  • -mtime: Search by modification time.
• Examples:
  • find /home -name '*.jpg'
  • find /var/log -size +1M
  • find /var/log -mtime -30

Searching Within Files

grep Command

• Usage: Search text using patterns.
• Flags:
  • -i: Case insensitive.
  • -r: Recursive.
• Examples:
  • grep 'search_string' file
  • grep -r 'search_string' /path/to/directory

Archiving and Compression

Creating Archives

tar Command

• Usage: Create and manage archives.
• Flags:
  • -c: Create.
  • -x: Extract.
  • -z: Compress with gzip.
  • -f: Specify filename.
• Examples:
  • tar -czf archive.tar.gz /path/to/directory
  • tar -xzf archive.tar.gz

Compressing Files

gzip Command

• Usage: Compress files.
• Flags:
  • -d: Decompress.
• Examples:
  • gzip filename
  • gzip -d filename.gz

User and Group Management

Adding and Deleting Users

useradd and userdel Commands

• Usage: Add and delete users.
• Flags:
  • -m: Create home directory.
  • -G [group]: Add to group.
  • -e [date]: Set account expiration date.
• Examples:
  • useradd -m -G root username
  • userdel -r username

Adding and Deleting Groups

groupadd and groupdel Commands

• Usage: Add and delete groups.
• Examples:
  • groupadd groupname
  • groupdel groupname