Essential Linux Commands for Cybersecurity

Introduction

• Goal: Master essential Linux commands before advancing to tools like Metasploit, nmap, Hydra, etc.
• Importance: Foundational knowledge for ethical hacking and cybersecurity.

Navigation Commands

LS Command

• Basic: ls lists directory contents.
• Flags:
  • -l: Long listing format (file type, permissions, owner, size, modification date).
  • -a: Includes hidden files.
  • -t: Sorts by modification time.
  • -h: Human-readable sizes.
  • Combined: ls -lath.

CD Command

• Basic: cd changes directories.
• Usage:
  • cd ..: Move up one directory level.
  • cd -: Return to the previous directory.
  • cd ~: Go to the home directory.
  • Tab completion helps navigate directories.

CLEAR Command

• Usage: clear clears the terminal screen.

PWD Command

• Usage: pwd prints the current working directory.

File Manipulation Commands

TOUCH Command

• Usage: touch filename creates a blank text file.

MKDIR Command

• Usage: mkdir directory_name creates a directory.
• Flags:
  • -p: Creates parent directories as needed.
  • -m: Sets permissions at creation.

CP Command

• Basic: cp source destination copies files.
• Flags:
  • -r: Copies directories recursively.
  • -f: Forces the copy, overwriting existing files.

MV Command

• Usage: mv source destination moves or renames files/directories.

RM Command

• Basic: rm filename removes files.
• Flags:
  • -r: Removes directories recursively.
  • -f: Forces removal without prompt.

CHMOD Command

• Usage: chmod mode filename changes file permissions.
• Modes: r (read), w (write), x (execute). Numeric: chmod 777 filename.

CHOWN Command

• Usage: chown owner:group filename changes file ownership.

Viewing File Contents

CAT Command

• Usage: cat filename displays file contents.
• Combining: cat file1 file2 > newfile.
• Appending: cat file3 >> newfile.

TAIL Command

• Usage: tail filename displays the last 10 lines of a file.
• Flags: -n for number of lines. -f for continuous updates.

HEAD Command

• Usage: head filename displays the first 10 lines of a file.
• Flags: -n for number of lines.

LESS and MORE Commands

• Usage: less filename or more filename to view large files one page at a time.
• Search: Within less, use /pattern to search.

Text Editors

VI Editor

• Usage: vi filename opens VI editor.
• Modes: i for insert, Esc to exit insert, :wq to save and quit.

NANO Editor

• Usage: nano filename opens Nano editor.

Process Management

PS Command

• Usage: ps lists processes for the current user.
• Flags: aux for detailed process list.

TOP Command

• Usage: top shows real-time process information.
• Interactive: u for user-specific processes, p for specific PID.

KILL Command

• Usage: kill PID to terminate processes.
• Flags: -9 for forceful termination, -2 for interrupt.

JOBS and FG Commands

• Usage: jobs lists background jobs. fg %1 brings job to the foreground.

Networking Commands

IP Command

• Usage: ip a shows IP addresses. ip route show shows routing table.
• Add route: ip route add subnet via gateway dev device.
• Add IP: ip addr add address dev device. Remove: ip addr del.

NETSTAT Command

• Usage: netstat -l for listening ports.
• SS Command: ss -t for TCP sockets.

SSH Command

• Usage: ssh user@hostname to connect via SSH.
• SCP Command: scp source destination for secure copy.

RSYNC Command

• Usage: rsync options source destination for file synchronization.

System Information

UNAME Command

• Usage: uname -a for detailed system information.

DF Command

• Usage: df -h shows disk space in human-readable format.

File Search Commands

FIND Command

• Usage: find directory -name pattern to search for files.
• Flags: -size to find by size, -mtime to find by modification time.

GREP Command

• Usage: grep pattern files to search within files.

TAR and GZIP Commands

• TAR:
  • tar czf archive.tar.gz files to create an archive.
  • tar xvf archive.tar.gz to extract.
  • tar rf archive.tar file to add to archive.
• GZIP:
  • gzip file to compress.
  • gunzip file.gz to decompress.

User Management

ADDUSER Command

• Usage: useradd username to add user.
• Flags: -m to create home directory, -g to add to group, -e to set expiration.

DELUSER Command

• Usage: userdel username to delete user.
• Flags: -r to remove home directory.

GROUPADD Command

• Usage: groupadd groupname to add group.

GROUPDEL Command

• Usage: groupdel groupname to delete group.

Conclusion

• Summary: Master these commands as a foundation for Linux system administration and cybersecurity roles.
• Encouragement: Practice regularly to build proficiency.