So the ancient Dell E1405 laptop on the Electronics Bench, connected to this-and-that, woke up without network connections. As in, right after booting, the link and activity lights jammed on solid, the usual
eth0 device wasn’t there, WiFi was defunct, and nothing made any difference.
After a bit of searching, the best summary of what to do appears on the Ubuntu forums. The gist of the story, so I need not search quite so much the next time, goes like this:
The laptop uses the Broadcom BCM4401 Ethernet and BCM4311 WiFi chips, which require the non-free Broadcom firmware found in the
linux-nonfree-firmware package. There’s a proprietary alternative in
bcmwl-kernel-source that apparently works well for most Broadcom chips, but not this particular set.
Guess which driver installed itself as part of the previous update?
The key steps:
sudo apt-get purge bcmwl-kernel-source egrep 'blacklist (b43|ssb)' /etc/modprobe.d/* ... then manually kill any files that appear ...
Apparently that problem has been tripping people for at least the last four years. That this is the 14.04 Long Term Support version evidently has little to do with anything at all.
While I was at it, I deleted all the nVidia packages that somehow installed themselves without my noticing; the laptop has Intel 945 integrated graphics hardware.
I vaguely recall what I intended to do before this happened…