Essential Linux Commands for Cyber Security

Introduction

• Focus: Essential Linux commands with special flags.
• Importance: Basis for advanced tools like Metasploit, Nmap, Hydra.
• Approach: Use terminal over GUI for navigation.

Navigation Commands

ls

• Basic Command: Lists directory contents.
• Flags:
  • -l: Long listing format (detailed info).
  • -a: Shows hidden files.
  • -t: Sort by modification time.
  • -h: Human-readable file sizes.
  • -r: Recursively list directory contents.

cd

• Basic Command: Change directory.
• Tips:
  • cd -: Go to the previous directory.
  • cd ..: Move up one directory level.
  • cd ~: Go to the home directory.
  • Tab completion: Use Tab to auto-complete directory names.

pwd

• Command: Print working directory.
• Usage: Shows the full path of the current directory.

File and Directory Management

touch

• Command: Create empty files.
• Example: touch test1.txt test2.txt

mkdir

• Command: Create directories.
• Flags:
  • -p: Create parent directories as needed.
  • -m: Set file permissions.

cp

• Command: Copy files and directories.
• Flags:
  • -r: Recursively copy directories.
  • -f: Force overwrite existing files.

rm

• Command: Remove files and directories.
• Flags:
  • -r: Recursively delete directories.
  • -f: Force deletion.
• Usage: Be cautious with rm -rf / as it can delete the entire system.

mv

• Command: Move or rename files and directories.
• Usage: mv oldname newname or mv file /newpath/

Permissions and Ownership

chmod

• Command: Change file permissions.
• Usage: chmod u+x file (give execute permission to the user).
• Flags:
  • u: User
  • g: Group
  • o: Others
  • +: Add permission
  • -: Remove permission

chown

• Command: Change file owner and group.
• Usage: chown user:group file

Viewing File Contents

cat

• Command: Display file contents.
• Usage: cat file
• Additional Features: Concatenate files and redirect output.

tail

• Command: Display the last part of a file.
• Flags:
  • -n: Number of lines to display.
  • -f: Follow file updates in real-time.

head

• Command: Display the first part of a file.
• Flags:
  • -n: Number of lines to display.

less and more

• Commands: Page through text one screen at a time.
• Usage: less file, more file
• Note: less is more functional.

Disk Usage

du

• Command: Disk usage of files and directories.
• Flags:
  • -h: Human-readable sizes.
  • -s: Summary of a directory.

df

• Command: Report file system disk space usage.
• Flags:
  • -h: Human-readable sizes.
  • -T: Include file system type.

Networking

ifconfig and ip

• Commands: Display or configure network interfaces.
• Usage: ip addr show (preferred over ifconfig)

ping

• Command: Check network connectivity.
• Usage: ping hostname

netstat and ss

• Commands: Network statistics and socket statistics.
• Usage: netstat -l, ss -t

ssh and scp

• Commands: Secure shell and secure copy.
• Usage: ssh user@host, scp file user@host:/path

Process Management

ps

• Command: Display information about active processes.
• Flags:
  • aux: Detailed information about all processes.

top

• Command: Display tasks and system resource usage in real-time.
• Usage: top, top -u username

kill

• Command: Terminate a process.
• Flags:
  • -9: Forcefully kill a process.
• Usage: kill pid, kill -9 pid

jobs and bg/fg

• Commands: Manage background jobs.
• Usage: jobs, bg jobnum, fg jobnum

Archiving and Compression

tar

• Command: Archive files.
• Flags:
  • -c: Create an archive.
  • -x: Extract an archive.
  • -f: Specify filename.
  • -z: Compress the archive with gzip.

gzip and gunzip

• Commands: Compress and decompress files.
• Usage: gzip file, gunzip file

Finding Files

find

• Command: Search for files in a directory hierarchy.
• Usage: find /dir -name filename
• Flags:
  • -size: Search by size.
  • -mtime: Search by modification time.

grep

• Command: Search text using patterns.
• Usage: grep pattern file

User Management

useradd and userdel

• Commands: Add and delete users.
• Flags:
  • -m: Create home directory.
  • -e: Set account expiration date.
• Usage: useradd username, userdel username

groupadd and groupdel

• Commands: Add and delete groups.
• Usage: groupadd groupname, groupdel groupname

Conclusion

• Goal: Become proficient in these essential commands before advancing to more complex tools.
• Additional Resources: Check out more advanced videos and tutorials on specific tools and commands.