How can I check the port number on a Linux server?

To check the port number on a Linux server, you can use the following command:

1. Use the command netstat: netstat -tuln. This will display all listening ports and their corresponding services.
2. To quickly list the ports that are being listened on, use the command ss -tuln.
3. Use the nmap command: nmap localhost. This will scan all open ports on the local host.
4. Check the /etc/services file: this file contains common port numbers and their corresponding services.

Please note that these commands need to be run under a user with sufficient privileges, such as the root user or a user with network administrator permissions.