Because the topic comes up regularly here I decided to create a guide on how to edit photos from multiple computers: darktable user manual - using multiple computers
I am looking for feedback - especially by people actually using multiple machines and are syncing between them 
.
I am using a Mac, and using Proton Drive (but would work the same with iCloud) to sync all my raw photo’s, xmp and darktable config folder.
All the paths are the same on the all machines, this was really important to get to work.
I have set the darktable config folder to be offline available always.
And this setup just works great. Just have to be aware that I can’t use them truely simultaneously, before switching to a different system the syncing to proton has to be done.
One added bonus feature is that I don’t need to have a local copy of my raw file of a photo, but still (as long I have internet) can edit it. It will download it when I need it. This gives that I have a larger folder with raw files then I would able to store on my laptop but still have access to all my raw files.
Do you think anything is missing from the guide?
I tried it a few ways in the past with all windows machines and sooner or later sync issues would corrupt things so gave up…mostly OneDrive issues I think…it would report that things were synced/ up-to-date when they were not and then I would get random version mismatch errors
The second approach is pretty much what I’m using between by desktop and my laptop with Nextcloud as sync-service. Both machines are running the same Linux distribution, so I can even work with symlinks to get the config-directory into the right place (i.e. linked into its proper place from within the generic Nextcloud-folder).
I think you properly describe the caveats: do not run simultaneously, always wait for the sync to finish (I only ever run into issues if I forget this or the sync fails for some reason), and some settings are machine-dependent and will get reset (OpenCL setting is the one for me - I always need to switch to “Very fast GPU” again once I switch machines, as the two have different GPUs).
There is one aspect missing, though: updating the thumbnails. I have not fully investigated the root cause yet, but I frequently face the situation where I have edited images on one machine, then switch to the other machine - and all those images look like they haven’t been touched yet (i.e. standard pre-view is displayed). The edits are all there if I open such an image in darkroom, so no issues there - just the thumbnail doesn’t get updated automatically.
Looks good to me!
I think the tumbnail cache lives in a separate directory. Thumbnail re-creation for the lighttable is AFAIk triggered upon import and upon edits in darktable. Maybe “re-scannig of xmp files” is not in the mix?
That’s what it feels like, yes. And to the best of my knowledge, you’re right about the thumbnail cache - in my case, I would like to avoid syncing that as well, as the two machines do not have the same access to the libraries (the “workspace”, i.e. the sets I currently work on, is also synced between the machines via Nextcloud, but the local storage on one is smaller than on the other one, so there are less sets synced).