[Update 19 June 2012: Apple has now released Thunderbolt Software Update 1.2.1, with no change in the release notes. The assumption is of course that Apple fixed the problems, but until reports start to roll in, we won’t know for sure. -Adam]
Apple last week released Thunderbolt Software Update 1.2, with the single comment that it “Adds support for the Apple Thunderbolt to Gigabit Ethernet Adapter.” Although it’s unclear if all Thunderbolt-equipped Macs were affected, a number of people reported that installing the update caused a variety of strange boot-related problems (kernel panics, getting stuck at the gray boot screen, “Unexpected error” messages, and more). Regardless of the details, in each case, it seems that the Mac is rendered unusable, even thunderstruck. I’ve now heard from some people for whom the update did not cause any problems, but it’s still unclear what the difference may be between those who are and are not suffering boot failures. At press time, Apple had pulled the update and not yet offered an alternative.
In all the reports I’ve seen, reinstalling Lion fixes the problem. Boot into Recovery Mode by restarting while holding down Command-R. Once booted from Lion’s hidden Recovery HD volume, you can select Reinstall Mac OS X (if there is no Recovery HD volume, or it’s damaged, most Mac models introduced since 2010 support Lion Internet Recovery, which enables them to download a new Recovery HD image and boot from that). Of course, redownloading Lion from the Mac App Store will take quite some time, depending on the speed of your Internet connection. Once you have reinstalled Lion, you’ll need to run Software Update to bring everything up to date, all while avoiding the Thunderbolt Software Update 1.2, of course.
If you happen to have a second Mac available, you can also reportedly recover by reinstalling just the Mac OS X 10.7.4 Combo Update. To do this, connect the thunderstruck Mac to your working Mac via FireWire or Thunderbolt and restart the thunderstruck Mac while holding down the T key to put it into Target Disk Mode. Then, start the update, and select the thunderstruck Mac’s boot drive at the appropriate point in the installer. For more troubleshooting techniques and recovery details, see “Take Control of Troubleshooting Your Mac, Second Edition.”
It’s likely that an update will appear soon; either way, unless you absolutely need that Thunderbolt to Gigabit Ethernet Adapter (which works only with the MacBook Air with Thunderbolt and the just-released MacBook Pro with Retina Display anyway), there’s no reason to install this update — assuming it’s still somehow available to you — until we’ve seen a fix.
Thanks to alert reader Tom Barry for the heads-up!