[Hopefully this isn't something pre-announced that I just missed, but I did try to search for it first.]
We have a restriction on the the macOS High Sierra Installer and noticed starting on Tuesday a spike in the number of machines violating the restriction. All the Macs were running OS X 10.10.5, and I noticed that they had run Software Updates recently. When I check for updates the Macs, I see the following:
softwareupdate --list --all
Software Update Tool
Copyright 2002-2012 Apple Inc.
Finding available software
Software Update found the following new or updated software:
* Install macOS High Sierra-
macOS High Sierra ( ), 5106655K [recommended]
Apparently earlier this week Apple made High Sierra an UPDATE rather than an upgrade. This change appears to only be on OS X 10.10 Yosemite (presumably 10.10.5), as I had checked for this on OS X 10.9 Mavericks and OS X 10.11 El Capitan, and neither show "Install macOS High Sierra" when checking for updates.
If you don't want your Yosemite Macs to automatically upgrade to High Sierra, you can run this command: softwareupdate --ignore "Install macOS High Sierra" This will prevent High Sierra from appearing in the Updates tab of App Store.app and from installing when running updates.
