In one of the Jenkins labs I had to change the port from 8080 to 8090.
In the lab this was the config file path: /lib/systemd/system/jenkins.service
But in this article linux - how to change port number for Jenkins installation In Ubuntu 12.04 - Stack Overflow it is mentioned that the /etc/sysconfig/jenkins could be used. That doens’t work though, as the one suggested by your lab is the correct working one.
How these two config files relate to each other? I mean I’ve changed the sysconfig based one and it didn’t affect anything, only the .service file change was changing the port.