Essential Linux Commands for Cybersecurity

Overview

• Introduction to essential Linux commands for ethical hacking and cybersecurity
• Importance of mastering basic commands before moving to advanced tools
• Commands covered: ls, cd, pwd, mkdir, cp, rm, mv, du, chmod, chown, cat, tail, head, less, nano, ps, top, kill, bg, fg, ifconfig, ip, netstat, ss, ssh, scp, rsync, tar, gzip, find, grep

Navigation Commands

ls

• Basic usage: ls
• Flags:
  • ls -l: Long listing format
  • ls -a: Show hidden files
  • ls -t: Sort by modification time
  • ls -h: Human-readable format
  • Combined: ls -lath

cd

• Change directory: cd [directory]
• Go back to previous directory: cd -
• Go up one level: cd ..
• Go to home directory: cd
• Use tab for auto-completion of directory names

pwd

• Print working directory: pwd

File and Directory Management

touch

• Create empty files: touch file1 file2

mkdir

• Create directories: mkdir dir1
• Create nested directories: mkdir -p dir1/dir2/dir3
• Set permissions while creating: mkdir -m 777 dir1

cp

• Copy files: cp file1 file2
• Copy directories: cp -r dir1 dir2

rm

• Remove files: rm file1
• Remove directories: rm -r dir1
• Force removal: rm -rf dir1

mv

• Move or rename files: mv file1 file2
• Move files to directories: mv file1 dir1

du

• Disk usage: du
• Human-readable format: du -h
• Summary: du -sh

Permissions and Ownership

chmod

• Change permissions: chmod [permissions] file
• Add execute permission: chmod +x file

chown

• Change ownership: chown user:group file
• Change owner only: chown user file
• Change group only: chown :group file

Viewing and Editing Files

cat

• Display file contents: cat file
• Concatenate files: cat file1 file2 > file3
• Append files: cat file3 >> file1

tail

• Show end of file: tail file
• Specify number of lines: tail -n 20 file
• Follow file: tail -f file

head

• Show beginning of file: head file
• Specify number of lines: head -n 20 file

less and more

• View large files page by page: less file, more file
• Search within less: /search_term

nano and vi

• nano for simple text editing: nano file
• vi for more advanced editing: vi file
  • Insert mode: i
  • Save and exit: :wq
  • Exit without saving: :q!

Process Management

ps

• List processes: ps
• Detailed list: ps aux

top

• Interactive process viewer: top
• Filter by user: top -u username
• Filter by PID: top -p PID

kill

• Kill process: kill PID
• Force kill: kill -9 PID

bg and fg

• Send process to background: command &
• List background jobs: jobs
• Bring process to foreground: fg %job_number

Networking

ifconfig and ip

• Display network interfaces: ifconfig, ip addr
• Display routing table: ip route
• Add IP address: ip addr add IP/NETMASK dev INTERFACE

netstat and ss

• Display network connections: netstat -l, ss -t
• Display listening ports: ss -lt

ssh and scp

• SSH to remote host: ssh user@host
• Copy files over SSH: scp file user@host:/path

rsync

• Synchronize directories: rsync -av source/ destination/

File Compression

tar

• Create tar archive: tar -cvf archive.tar files
• Extract tar archive: tar -xvf archive.tar
• Create compressed tar: tar -czvf archive.tar.gz files

gzip

• Compress file: gzip file
• Decompress file: gunzip file.gz

Searching

find

• Find files: find /path -name 'filename'
• Find by size: find /path -size +1M
• Find by modification time: find /path -mtime -30

grep

• Search within files: grep 'pattern' file
• Recursive search in directory: grep -r 'pattern' /path

System Information

uname

• Display system information: uname -a

df

• Display disk space usage: df -h

User Management

useradd, usermod, userdel

• Add user: useradd username
• Create home directory: useradd -m username
• Set expiration date: useradd -e YYYY-MM-DD username
• Delete user: userdel username
• Delete user with home directory: userdel -r username

groupadd, groupdel

• Add group: groupadd groupname
• Delete group: groupdel groupname

Conclusion

• Importance of mastering these essential commands
• Encouragement to practice and explore more advanced topics in cybersecurity