Underneath every command here sits one more program, and all the others have to ask it for things.
Operating system
Also called OS, macOS, Linux, Kernel
The program that runs the machine: it shares out the CPU and memory, keeps files on the disk, and starts and stops processes. macOS, Linux and Windows are operating systems. Programs ask it for everything, so a program built for one often won't run on another.
Your agent may run on a Mac while the code ships to Linux, and the two differ in small ways that pass on your laptop and then fail on a server. Agents write commands for one system out of habit, so tell yours what the target is.
“CI runs on Ubuntu and I am on a Mac. Don't use sed -i or anything else that differs between them: do this edit in a small Node script, and check that every import matches its file name's exact capitals.”