How do I force Photos on macOS to continue syncing?

No; freeing up storage is not what I wanted to do. I wanted to make Photos ignore the low storage.

I have tested a solution, and it seemed to have worked:

1. Create a sparse disk image

hdiutil create \
  -size 1t \
  -type SPARSEBUNDLE \
  -fs APFS \
  -volname FakeStorage \
  ~/FakeStorage.sparsebundle

2. Mount the image

3. Move your photos library to it

4. Point the Photos app to the new library

5. Syncing will begin!

A big disclaimer is that if you actually run out of physical space, the library might become corrupted; it'll most likely be repairable with the built-in tools, but it's still a risk.

20gb is not "crippling", and even if it were, that doesn't really matter. It is plenty to sync a handful of photos, which is why I'm looking for a workaround to force trigger syncing despite the seemingly hard-coded limits.

Btw, at ~23-25gb free Photos started syncing again.

Since I still find the problem interesting, I have tried looking into ways to spoof free storage reported to Photos. So far the only seemingly viable option is creating and mounting a virtual disk reporting larger storage than physically available as free space, then moving the Photos library onto it. Not worth it for the current use-case, but I'm saving the solution if there's ever a time when I need sync to work immediately.

Disabling SIP and figuring out a way to inject modified a library with modified `statsfs()` calls could potentially work, but it is ridiculously complicated for something that should be much simpler.

Have you already enabled the option "Optimize Mac Storage" for iCloud Photos in the Settings > Photos? If you are using "Download originals" , it can help to switch temporarily to "Optimize Mac Storage" instead, until all items have been synced properly. "Optimize Mac Storage" can help, if you are low on local storage on your Mac, but not, if you are low on storage in iCloud.

10% of 512GB is 52 GB. You need at least that free. 20 GB is not lowish, it is crippling.

circoplomber wrote: …It's complaining that I'm low on storage,

Then that's probably the problem. Many operations use the Mac's empty storage space to move files around. If you run out of storage, then those operations may not be able to be completed and, ironically, that can mean that even deleting doesn't work. If you have less than 10% available, then things can get lost forever. I have found that having 120GB free of 1TB is not actually enough. I try to keep at least 15% of my storage space free.

What is your storage on this Mac? At System Settings>General> Storage, my Mac says 745 GB of 1TBB used. What does yours say?

circoplomber wrote:

I do actually have low-ish free storage, about 20gigs out of 512, low but should be enough for the ~3 photos I want synced.

Good computer practice to keep about 80-100 GB of free space on the boot drive to facilitate optimal system and application performance.

You can get an external drive, SSD or HDD, to move the larger folders, Pictures, Music, Movies, to.

We understand. However, everyone has been telling you how to achieve what you want. Without extra storage the syncing will not be possible.

20GB free storage is not even enough to run any updates or upgrades. As told previously one should see 80-100 GB free to promote optimal system and application performance.

I've already tried:

• Combing through defaults to see if there are any keys I could overwrite to change/ignore the threshold
• Restarting the photo library daemons to force a fresh storage check
• Purposefully creating then deleting a large file to trigger storage evaluation

I also combed through the logs for Photos and all processes that could be related to iCloud sync, trying to find where the storage check happens, but came up with nothing.

I do actually have low-ish free storage, about 20gigs out of 512, low but should be enough for the ~3 photos I want synced.

I'm specifically looking for a way to bypass the check and force Photos to sync.

It seems like everybody misunderstands what I'm looking for. I know I'm low on storage, and I'm aware of how it can be fixed. I'm looking for a way to make the Photos app ignore the low storage and sync anyways.

I agree that macOS is god awful at storage management, but it's not that bad that it'll just start randomly deleting your files if you're low on storage. It'll just limit some functionality, which is specficially the limitation I'm trying to circumvent.

Re-read what I wrote about the need for free storage space. As long as you have only 20GB free, your files will be in peril.