Essential Linux Commands for Cybersecurity Professionals

Introduction

• Presenter: Neilson Networking
• Topic: Essential Linux commands for ethical hacking and cybersecurity
• Goal: Mastering these basic commands before moving on to advanced tools like Metasploit, nmap, Hydra, etc.

Navigating the Linux File System

Opening the Terminal

• Preferred Method: Use the terminal over GUI file explorers.

ls Command

• Basic Usage: ls lists directory contents.
• Flags: -l: Long listing format.
• Explanation of Long Listing: (ls -l)
  • l: Link
  • Permissions (read, write, execute) for owner, group, others
  • Owner and group
  • File size
  • Date modified
  • d: Directory indicator
• Flags: -a: Show hidden files.
• Flags: -t: Sort by time modified.
• Flags: -h: Human-readable sizes.
• Combining Flags: ls -lath to combine multiple flags.

cd Command

• Basic Usage: Change directory
• Example Usage:
  • cd /etc to change to the etc directory
  • cd - to go back to the previous directory
  • cd .. to go up one level
  • cd to go to home directory
• Tips: Using tab for auto-completion

pwd Command

• Usage: Print working directory

Manipulating Files and Directories

touch Command

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

mkdir Command

• Usage: Create directories
• Example:
  • mkdir dir1 to create a single directory
  • mkdir -p parent/child to create nested directories
  • mkdir -m 777 dir to set permissions

cp Command

• Usage: Copy files and directories
• Example:
  • cp file1 file2 to copy a file
  • cp -r dir1 dir2 to copy directories recursively

rm Command

• Usage: Remove files and directories
• Example:
  • rm file1 to remove a file
  • rm -r dir1 to remove a directory recursively
  • rm file* to remove files with a pattern

mv Command

• Usage: Move or rename files
• Example:
  • mv oldname newname to rename
  • mv file1 dir to move a file

du Command

• Usage: Disk usage
• Example:
  • du -h for human-readable format
  • du -sh for summary

File Permissions

chmod Command

• Usage: Change file permissions
• Example:
  • chmod o-wx bad_dir to remove write/execute for others
  • chmod g+x file1 to add execute for group
  • chmod 777 file1 for full permissions

chown Command

• Usage: Change file ownership
• Example:
  • chown user file to change owner
  • chown user:group file to change owner and group

Viewing Files

cat Command

• Usage: View file contents
• Example:
  • cat file1 to view content
  • cat file1 file2 > file3 to concatenate
  • cat file1 >> file3 to append

tail Command

• Usage: View end of file
• Example:
  • tail file1 to view last 10 lines
  • tail -n 15 file1 for last 15 lines
  • tail -f file1 for continuous updates

head Command

• Usage: View beginning of file
• Example:
  • head file1 for first 10 lines
  • head -n 15 file1 for first 15 lines

less and more Commands

• Usage: View large files page by page
• Example:
  • less file or more file
  • Navigation using space for next page
  • Search within less using / command

Text Editors

• Editors: vi, nano
• vi: More complex but powerful
  • i to insert, esc to exit insert mode, :wq to save and quit
• nano: User-friendly
  • ctrl + x to exit, y to confirm save

Process Management

ps Command

• Usage: View current processes
• Example:
  • ps aux for detailed view
• Columns: User, PID, CPU%, MEM%, VSZ, RSS, TTY, STAT, START, TIME, COMMAND
• Filtering: ps aux | grep process_name

top Command

• Usage: Interactive process viewer
• Example:
  • top to start
  • top -u username to filter by user
  • top -p PID to monitor a specific process
• Columns: Similar to ps, sorted by memory usage

Killing Processes

• Command: kill PID
• Force Kill: kill -9 PID
• Interrupt: kill -2 PID

Job Control

• Background Jobs: command &
• Listing Jobs: jobs
• Foreground: fg %job_number
• Example:
  • ping example.com &
  • fg %1 to bring to foreground

Networking Commands

• Ifconfig: Deprecated, use ip
• IP Address: ip addr
• Default Gateway: ip route show default
• Adding Routes: ip route add subnet via gateway dev iface
• Adding IP: ip addr add ip/mask dev iface
• Netstat: Deprecated, use ss
• Listening Ports: ss -lt for TCP, ss -lu for UDP
• SSH: ssh user@host, ssh -p port user@host
• SCP: Secure copy, scp file user@host:directory
• Rsync: File synchronization, rsync -options source destination

System Information

uname Command

• Usage: System information
• Example: uname -a for detailed info

Disk Usage

• Command: df
• Example:
  • df -h for human-readable format
  • df -Th for file system types

Searching Files

Find Command

• Usage: Search files
• Example:
  • find /path -name pattern
  • find /path -size +1M
  • find /path -mtime -30

Grep Command

• Usage: Search within file contents
• Example:
  • grep pattern file
  • grep -r pattern /path

Archiving and Compression

Tar Command

• Usage: Archive files
• Example:
  • tar czf archive.tar.gz files to create
  • tar xzf archive.tar.gz to extract
  • tar rf archive.tar file to add files

Gzip Command

• Usage: Compress files
• Example:
  • gzip file to compress
  • gunzip file.gz to decompress
  • gzip -l file.gz to list contents

User Management

Adding Users

• Command: useradd username
• Options:
  • -m to create home directory
  • -g group to add to group
  • -e YYYY-MM-DD to set expiration date

Deleting Users

• Command: userdel username
• Options: -r to remove home directory

Adding and Deleting Groups

• Commands: groupadd groupname, groupdel groupname

Conclusion

• Summary: Covered essential Linux commands for navigation, file manipulation, permissions, process management, networking, and user management.
• Recommendation: Master these commands for a strong foundation in Linux before moving on to advanced tools.
• Next Steps: Check out additional videos on advanced tools like Metasploit, nmap, etc.
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