This wasn't just limited to Linux either. It was a common UNIX trick :)
This is a bit of a lost art these days though. iLo, IPMI have replaced the need for serial. Then virtualisation and, to a lesser extent, containerisation have lowered the bar even further plus also moving the industry towards more ephemeral systems that can be destroyed and rebuilt automatically rather than the old habits of nursing failed hosts back to health.
[1] https://duckduckgo.com/?q=9+pin+d-sub+plug&t=newext&atb=v316...
[2] https://www.kernel.org/doc/html/v5.3/admin-guide/serial-cons... (a lot of distros at the time did ship a kernel with this support compiled in. I don't know how common it is now).