How to Create and Run New Service Units in Systemd

A few days ago, I came across a Centos 7 32-bit distro and I felt the desire to test it on an old 32-bit machine. After booting I realized that it had a bug and it was loosing the network connection, which I had to reset to “up” manually every time after boot.

So, the question was how could I set a script to do this job and run every time I booted my machine?