What is localhost? What do the numbers mean? Is there a pattern to how they are used?

Question

Hello,

I’m kind of confused about this.

I’ve noticed some programming software requires you to set up a server to run projects. MySQL runs on localhost:8080, PHP runs on localhost:4000. Are these numbers predetermined and specific to certain applications, or are they decided upon by the user? Can you know which software will use which number based on some kind of pattern?

In: 1

Answer 1

Local host is a host name used to refer to the loopback IP address of the machine its running on also you can use ip 127.0.0.1.

The numbers after the colon are the port numbers and for known services are normally a standard but can be custom if you want. https://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbers

Edit tried to keep it simple added more info