I've been a professional C, Perl, PHP and Python developer.
I'm an ex-sysadmin from the late 20th century.
These days I do more Javascript and CSS and whatnot, and promote UX and accessibility.
I worked for a while on recovering an application from a running server which hadn't ever been turned off and had "started making funny noises". I had to telnet to a SunOS box and grab the code and try to replicate functionality on a modern (well, modern for a few years ago) SUSE box. It wasn't just a case of updating the code, we weren't sure exactly how the system was supposed to work so I needed to run it in parallel on both systems to make sure my modifications weren't breaking functionality. That was fun :)
I don't know exactly but probably about a decade.
I worked for a while on recovering an application from a running server which hadn't ever been turned off and had "started making funny noises". I had to telnet to a SunOS box and grab the code and try to replicate functionality on a modern (well, modern for a few years ago) SUSE box. It wasn't just a case of updating the code, we weren't sure exactly how the system was supposed to work so I needed to run it in parallel on both systems to make sure my modifications weren't breaking functionality. That was fun :)
That is some Sensei level stuff