Michael Tsai put together an excellent roundup of this weekend’s issue with iMac Ethernet drivers due to an automatic, pushed update from Apple.
Apple has support instructions for fixing the issue; however, they’re not straightforward enough for average users to follow —the simplest scenario requires the use of Terminal commands. In a more challenging situation, where the iMac cannot connect to WiFi, it’s necessary to dive into recovery mode. On top of that, as Tsai points out, Apple messed up their own instructions:
Note that Apple’s example
rm -rfcommand is incorrect. You should use straight quotes rather than smart quotes.
Not their finest hour.