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If you’re running macOS 10.12 Sierra or earlier, and do not want to upgrade to 10.13 High Sierra right now, be careful because Apple has started pushing High Sierra to older Macs and making it easy to upgrade inadvertently. In short, if you get a macOS notification asking you to install High Sierra, click the Details button to launch the App Store app, and then quit it.





Here’s the story.

I realized this was happening because I’m testing Watchman Monitoring, an app and service used by Apple consultants, managed service providers (MSP), and large Mac-using organizations. Watchman Monitoring sits in the background, looking for events of interest on a Mac and notifying the consultant, MSP, or IT admin who’s responsible for keeping that Mac running. I have Watchman keeping an eye on all of our Macs, my parents’ Macs, and my aunt and uncle’s Macs — in other words, the Macs that I’ll have to fix if something goes wrong.

The first hint was an email from Watchman Monitoring telling me that my aunt’s Mac had started downloading the High Sierra installer. I was surprised, since she’s quite capable on her Mac but never undertakes major upgrades without asking me first. I saw that message while on a plane to MacTech Conference, and once I had landed in Los Angeles, I received additional messages from Watchman telling me that my father’s and uncle’s Macs had also downloaded High Sierra. That was too many simultaneous instances to be anything but an automatic push from Apple.





Happily, because I was flying to MacTech, within minutes of arriving at the hotel, I’d run into Watchman Monitoring’s Allen Hancock, who confirmed my suspicion that Apple was pushing out High Sierra updates. Additional details became available while talking to Jason Dettbarn, CEO of device management firm Addigy, since Addigy’s consultant and MSP customers who had used Addigy to block unauthorized macOS upgrades were scrambling to explain what was going on to their users. (At least they weren’t scrambling to deal with a bunch of users inappropriately installing High Sierra!)

What happens is that Apple’s Software Update automatically downloads High Sierra in the background and then presents the notification shown at the top of this article to the user, offering just two choices: Install and Details.

If you don’t want to install, the only way to cancel is to click Details, which launches the App Store app and displays the High Sierra description, and then quit App Store. That’s confusing — Apple should instead present a Cancel button.

You almost certainly don’t want to click Install when that notification appears. Regardless of your opinion of High Sierra, installing it will take quite some time — an hour or more — and you should make sure you have a backup before starting, as per Joe Kissell’s advice in “Take Control of Upgrading to High Sierra.”

This automatic upgrade behavior may be annoying, but it was possible with Sierra as well, although no one I’ve talked to remembers Apple pushing Sierra in the same way. Apple explains it in a support document — it’s tied to the “Download newly available updates in the background” checkbox in System Preferences > App Store. There’s no real harm in deselecting that checkbox — you’ll just have to wait for updates to download when you decide to install. That may be better than using limited bandwidth for an unexpected 5 GB download.





(Do not disable “Install system data and security updates” because that option is essential for protecting your Mac against patched security vulnerabilities (see “Make Sure You’re Getting OS X Security Data,” 30 March 2016).)

Since I’m traveling, it has been difficult to verify certain details. However, TidBITS reader Curtis Wilcox confirmed that the full 5.21 GB Install macOS High Sierra app is downloaded to the Applications folder. If you need the disk space back, you can delete it from there, or later launch it manually when you’re ready to upgrade to High Sierra.

High Sierra has been out for less than two months and has received two updates so far, as detailed in “macOS High Sierra 10.13 Supplemental Update Fixes Early Bugs” (5 October 2017) and “macOS 10.13.1 High Sierra Offers Minor Fixes and More Emoji” (1 November 2017). Both seemed highly targeted, so it seems likely that the next update will address more bugs and may get to the point where more IT admins and consultants recommend upgrading to it.

Apple is clearly trying to move macOS in the direction of iOS, where upgrades are difficult to avoid. However, macOS is a much more complex environment and one that’s usually more important to people’s livelihoods, so we recommend approaching upgrades carefully. Presenting people with a one-click install that offers no chance to back up first and that will take hours of time prioritizes ease of use over doing what’s best for the user, and that’s a dangerous tradeoff.