Updated May 27th, 2016.
I’m seeing a lot of problems with Apple’s 10.11.3 update. If you’ve already installed the 10.11.3 update and everything seems fine, consider yourself lucky; if you haven’t installed it, play it safe and don’t install it. I’ve never seen a more problematic update.
UPDATE: the 10.11.4 update is out and I’ve seen zero problems with it. Read “Should I Update My Mac to 10.11.4” for more info.
UPDATE #2: now we’re at 10.11.5. It too has no problems. See my article about how to install 10.11.5 the pro way.
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You’re probably wondering what’s so bad about the 10.11.3 update. Well, nothing— unless you’d call a Mac that won’t start something to be concerned about! When things go wrong with 10.11.3, they go wrong very quietly– the update appears to install, and then the Mac restarts, which is totally normal— but then it doesn’t finish restarting. It gets about 75% of the way through the startup and stops. Turning the Mac off and on again doesn’t help. Repairing the disk after starting from the Recovery Disk sometimes helps; reinstalling the system sometimes helps; waiting a really long time sometimes helps. In my case, I had to reinstall the system, and then delete my own user from the system, and then restore my user from a Time Machine backup. It took a long time. See below.
If you simply must be 100% up-to-date, and can’t bear to be on 10.11.2, give yourself the best chance possible by installing 10.11.3 via the 10.11.3 Combo Update, the way the big boys do (except when the big boys are lazy and complacent, as I was when I updated using Apple’s automatic Software Update last week.)
Combo Updates include everything needed to take you from the base system to the current version. In this case, it means it has everything needed to take you from 10.11.0 to 10.11.3. The automatic update only contains what’s necessary to go from 10.11.2 to 10.11.3. Installing stuff that you already have (such as the stuff that got you to 10.11.0 to 10.11.2) might seem like a waste of time but in my experience, it never makes things worse. In a way, with Combo Updates you’re refreshing the system, and that’s good. Combo Updates are always available but never via the automatic Software Update mechanism. Instead, you have to search for them on Apple’s site. I’ve done the work for you here— use my Big Blue Button.
Personally, in the case of 10.11.3 I wouldn’t even do the Combo Update. I’d wait for 10.11.4. In addition to my own misadventure with it, I’ve seen three Macs with the same won’t-start-all-the-way symptom, and I’ve read about another one (Adam Engst’s, he of the TidBITS newsletter fame). That’s more trouble than I’ve seen for any Apple update in 25 years of helping people with their Macs.
Do yourself a favor and steer clear of the 10.11.3 update. Do your friends a favor and tell them to steer clear too. Do it the easy way with the sharing buttons below.