Mac/Linux and Golang : Fix bind: address already in use error

Not really a tutorial. However, it is good to put this here as a guide for junior software developers.

Saw this message in one of the Facebook group that I'm helping out as administrator:

I'm trying to create a simple REST API using go. Everytime I save and run the file, I get this error

"bind: address already in use"

I then have to go and change the port address. Problem is that everytime I make a change to the file it gives the error. So on making successive changes to the file I have to successively come up with port addresses and change that in the file

The OP is struggling to understand why his/her program works when running for the first time and then unable to run for the second time.

Diagnostic:

Because the OP did not show his/her source code, I can only speculate that the program that the person trying to run stayed in memory and hogged the port address. The left over process(program) is also known as zombie process.

Solution:

If on Linux, try using this command to find out the process ID.

$sudo lsof -n -i :<port number>

On MacOSX:

$lsof -i tcp:<port no>

Once you find out the PID(process identifier) of your zombified Golang program, kill it with

$kill -9 <PID>

Try to relaunch the program again with the same port address after killing the hoggers and it should run with complaining:

"bind: address already in use"