Early days of "open source"
IBM used to send the OS with all its source code which had to be assembled and then installed. This allowed a variety of code modifications to be made by the local site. User groups would publish mods that could be made to "Improve" the system. While attempting to implement job accounting with a "low impact" mod that used the S/360 Channel Programming to bypass the majority of the OS I/O scheduling, 'someone' managed to make the offending disk drive unavailable. Unfortunately, it was the host drive for the OS. It took several re-boots of the massive machine to obliterate and correct the situation. And that's why we worked weekends. Never could convince my wife of that.