Essential Linux Commands for Cybersecurity

Introduction

• Focus on essential Linux commands and flags to enhance your skills
• Important for ethical hacking and cybersecurity
• Recommended to master these before advancing to tools like Metasploit or nmap

Navigating the File System

Using ls Command

• Basic command to list directory contents
• ls -l: Long listing format
  • Shows file type, permissions, owner, group, size, and modification date
• ls -a: Includes hidden files (those starting with a dot)
• ls -t: Sorts files by modification time
• ls -h: Human-readable sizes
• ls -R: Recursively lists directory contents

Using cd Command

• Change directory command
• cd -: Go back to the previous directory
• cd ..: Move up one directory level
• cd ~: Go to the home directory
• Tab completion: Autocomplete directory names

pwd Command

• Displays the current working directory

clear Command

• Clears the terminal screen

Manipulating Files and Directories

Creating Files and Directories

• touch filename: Creates an empty file
• mkdir directoryname: Creates a new directory
• mkdir -p directory/subdirectory: Creates nested directories
• mkdir -m permissions directory: Creates a directory with specific permissions

Copying Files and Directories

• cp source destination: Copy files
• cp -r source destination: Recursively copy directories

Removing Files and Directories

• rm filename: Removes a file
• rm -r directory: Recursively removes a directory and its contents
• rm -rf directory: Forcefully removes directory and contents (be cautious)

Moving and Renaming Files

• mv source destination: Move or rename files

Viewing and Editing Files

Viewing File Contents

• cat filename: Displays file contents
• cat file1 file2 > newfile: Concatenates files
• cat file >> existingfile: Appends a file to an existing file
• tail filename: Shows the last 10 lines of a file
• tail -n number filename: Shows the last 'number' of lines
• tail -f filename: Continuously monitors a file for changes
• head filename: Shows the first 10 lines of a file
• head -n number filename: Shows the first 'number' of lines
• less filename: Opens file in a scrollable view
• more filename: Similar to less, but simpler

Editing Files

• vi filename: Opens file in vi editor
• nano filename: Opens file in nano editor (easier for beginners)

Process Management

Viewing Processes

• ps: Lists processes for the current user
• ps aux: Detailed process information for all users
• top: Interactive process viewer
• htop: An enhanced version of top (if installed)

Managing Processes

• kill PID: Kill a process by its process ID
• kill -9 PID: Force kill a process
• jobs: Lists background jobs
• fg %jobnumber: Brings a background job to the foreground
• bg %jobnumber: Sends a job to the background

Networking Commands

Basic Networking

• ifconfig: Displays network interfaces (deprecated)
• ip a: Shows IP addresses
• ip route: Shows routing table
• ping hostname: Checks connectivity
• traceroute hostname: Traces route to a host

SSH and SCP

• ssh user@host: Connects to a remote host via SSH
• scp source user@host:destination: Securely copies files between hosts

Monitoring Network Connections

• netstat -l: Shows listening ports
• ss -t: Shows TCP connections
• ss -u: Shows UDP connections

Checking System Information

Disk Usage

• df -h: Shows disk usage in human-readable format
• du -sh directory: Shows disk usage of a directory

System Information

• uname -a: Displays system information

Searching and Finding Files

Find Command

• find /path -name filename: Searches for files by name
• find /path -size +1M: Finds files larger than 1MB
• find /path -mtime -30: Finds files modified within the last 30 days

Grep Command

• grep pattern filename: Searches for a pattern in a file
• grep -r pattern directory: Recursively searches for a pattern in a directory

Archiving and Compressing Files

Tar and Gzip

• tar czf archive.tar.gz /path: Creates a compressed tar archive
• tar xzf archive.tar.gz: Extracts a compressed tar archive
• gzip filename: Compresses a file
• gunzip filename.gz: Decompresses a file

User Management

Adding and Deleting Users

• useradd username: Adds a new user
• userdel username: Deletes a user
• usermod -aG groupname username: Adds a user to a group

Adding and Deleting Groups

• groupadd groupname: Adds a new group
• groupdel groupname: Deletes a group

Conclusion

• Mastering these basic commands is essential before moving on to more advanced tools.
• Practice these commands to gain confidence and efficiency in using Linux for cybersecurity tasks.
• Check out additional videos and resources for more in-depth tutorials on specific topics.