1. passwd Command:

Changes a user’s password.

Example:

passwd username

2. useradd Command:

Creates a new user account.

Example:-

useradd username

3. userdel Command

Deletes a user account.

Example :-

userdel username

4. groupadd Command:

Creates a new group.

groupadd groupname

5. groupdel Command

Deletes a group.

Example :-

groupdel groupname

6. chmod Command:

Changes file permissions.

Example :-

chmod 600 file.txt

7. chown Command

Changes the owner of a file or directory.

Example

chown user:group file.txt

8. chgrp Command

Changes the group ownership of a file or directory.

Example

chgrp groupname file.txt

9. ssh Command

Securely connects to a remote server.

Example:-

ssh user@hostname

10 . scp Command

Securely copies files between hosts.

Example :-

scp file.txt user@hostname:/destination/path

11. ufw Command:

Uncomplicated Firewall, a user-friendly interface to manage iptables firewall.

Example :-

ufw enable

12. iptables Command

Configures firewall rules.

Example :-

iptables -A INPUT -p tcp --dport 22 -j ACCEPT

13. fail2ban Command

Protects against brute-force attacks by monitoring logs and blocking malicious IP addresses.

Example :-

fail2ban-client status

14. sudo Command

Allows users to execute commands with superuser privileges.

Example :-

sudo command

15. ssh-keygen Command

Generates SSH key pairs for authentication

Example:-

ssh-keygen -t rsa

16. chown Command:

chown stands for “change owner.” It is used to change the owner of a file or directory.
Example:

chown user:group file.txt

17. chgrp Command:

chgrp stands for “change group.” It is used to change the group ownership of a file or directory.
Example:

chgrp group file.txt

18. find Command:

find is used to search for files and directories in a directory hierarchy.
Example:

find /path/to/search -name "file.txt"

19. locate Command:

locate is used to find files by name.
Example:

locate file.txt

20. du Command:

du stands for “disk usage.” It is used to display the disk usage of files and directories.
Example:

du -sh directory/

21 df Command:

df stands for “disk free.” It is used to display disk space usage and availability.
Example:

df -h

22. free Command:

free is used to display free and used memory in the system.
Example:

free -h

23. top Command:

top is used to display system processes and resource usage in real-time.
Example:

 top

24. ps Command:

ps is used to display a snapshot of current processes.
Example:

ps aux

25. kill Command:

kill is used to terminate processes.
Example:

kill PID

26. sudo Command:

sudo is used to execute a command as another user, typically the superuser.
Example:

sudo command

27 su Command:

su is used to switch user accounts or become the superuser.
Example:

su username

28. passwd Command:

passwd is used to change a user’s password.
Example:

passwd username

29. useradd Command:

useradd is used to create a new user account.
Example:

useradd username

30 userdel Command:

userdel is used to delete a user account.
Example:

userdel username

Thanks for learning 👍👍