Over the break, I upgraded my 2020 27-inch iMac to macOS 14 Sonoma, which I’ve been running on my M1 MacBook Air for months. The process was simple and easy, and everything continued to work with no hiccups. With one exception: Time Machine.
Shortly after I booted into Sonoma for the first time, Time Machine threw an error, claiming that it couldn’t back up.
Clicking the Details button revealed the reason why: iCloud Drive hadn’t finished syncing.
Although there wasn’t any apparent reason why iCloud Drive’s sync status should have changed from when I started the upgrade, it was clearly working away, as evidenced by the progress indicator when I clicked iCloud Drive in the sidebar.
“No problem,” I thought, “I’ll just wait for it to finish, and then all will be fine.” Unfortunately, even after iCloud Drive finished syncing, Time Machine continued to complain at me repeatedly, as backup after backup failed. Restarting didn’t resolve the problem, so I dug a little deeper.
I remembered that Howard Oakley had been writing quite a bit on his Eclectic Light Company blog about iCloud Drive recently, including articles about how Sonoma:
- radically changes how iCloud Drive works behind the scenes
- changes the behavior of Optimize Mac Storage
- separates controls for apps using iCloud Drive versus those using CloudKit
- adopts the File Provider technology that Apple has pushed other cloud storage services to use (see “Apple’s File Provider Forces Mac Cloud Storage Changes,” 10 March 2023)
However, the critical article focused on how Sonoma’s iCloud Drive changes could prevent Time Machine backups from completing. In it, he merely noted that Time Machine couldn’t back up until iCloud Drive had finished syncing, which I already knew wasn’t the entire story. In the comments, however, user whidbeythedog provided the answer: iCloud Drive must finish syncing on all the accounts on the Mac.
I always have a second troubleshooting account on all my Macs called “Ghost in the Machine.” The ghost account has full administrative permissions, but I keep it as pristine as possible beyond connecting it to my iCloud account. It’s handy when I need to eliminate an account-level preference file as a reason for some undesirable behavior and for making screenshots that lack most customizations I’ve made. (When I need to be sure I’m using a completely stock account, I log into a new guest account that I delete once I’m done.) Because I use the ghost account infrequently and don’t think of it as using iCloud Drive, it didn’t even occur to me as a variable until I read that blog comment.
Because the ghost account is logged into my iCloud account and has iCloud Drive turned on, it too needed to finish syncing before Time Machine could complete a backup. As soon as it did that—in the background, while I was logged into my primary account—Time Machine promptly started backing up again. Problem solved.
For a few others, the simple fix of logging into additional accounts and letting them finish syncing hasn’t been enough. In an Apple Support Communities discussion, a couple of people found that signing out of iCloud, rebooting, triggering a Time Machine backup, and then signing back in resolved the problem. I’d save that for a last resort because signing out of and back into iCloud is a recipe for confusion.
I’ve filed a bug report with Apple about this situation. Time Machine isn’t necessarily doing anything wrong here, but Apple could reduce confusion with better messaging that alerted users to the possibility of iCloud Drive needing to finish syncing on additional accounts. In an ideal world, of course, Time Machine would skip over iCloud Drive files that hadn’t yet synced and copy them on a subsequent run, but perhaps we’re running into a one-time conversion to the new File Provider approach that’s best handled all at once after iCloud Drive has caught up with itself.