What happened? On the local computer, Synctrayzor this morning reported “path exists, but folder marker missing” for my synchronized folder “A” for some unknown reason. In fact, the .stfolder file (or is it a folder?) was missing from the folder.
So I stopped Sync locally, copied the .stfolder from another synchronized folder over to the local “A” folder and restarted Sync.
A minute later I accidentally saw on the remote (source) machine that Sync was about to mass-delete (thousands) of files from the source folder.
Thanks to File Versioning I seem to have a backup of the deleted files (knock on wood). However, the file names all contain a ~tilde and the modification (deletion?) date, so I first have to think about how to restore the original file names, and then restore the files back to the source PC…
Most of all of course I would like to understand what went wrong here, and how it could happen that Sync would start to delete all files on the source machine?
What happened here is you’ve overridden the safety measures built in to prevent exactly this kind of situation, and got shot in the foot as the result.
Syncthing creates a folder marker (.stfolder) at the root of a directory it works with. This folder marker isn’t supposed to go anywhere, and if it disappears, Syncthing thinks something unexpected happened and stops. An example may be a folder on a removable device: if the device gets removed, the folder marker can no longer be seen, and that means no work should be done on this folder. When the device gets plugged in again, Syncthing sees the folder marker again and continues operation.
In your case it looks like something happened to your filesystem so that the directory containing your folder started appearing empty to Syncthing. Seeing no files in it, and no folder marker, Syncthing stopped its operation. Then you manually recreated the folder marker, so now Syncthing could see it, but still couldn’t see the files, so Syncthing interpreted the situation in the only possible logical way: there is the directory, it is accessible, but there are no files in it, which means the user (you) has deleted all the files while Syncthing was stopped. So, these files were reported as deleted by you to the other machine, and the other machine acted accordingly.
Thank you Evgeny for the quick answer and for the very comprehensible explanation!
In fact, something has happened to the local file system/sync folder: while still all of its subfolders are there, almost all are empty…
In other words, something has started to delete all files locally, including (here, fortunately) the .stfolder file. And after I re-created the .stfolder, Sync naturally started replicating the deletions on the source…
Now I will try to restore the files deleted today on the source machine, and then start troubleshooting…
Damn, this kind of situation just can’t happen anymore (to me)…!
It would be great to have a feature that warns you of mass-deletions…
Well, yeah, but the complaint is really that the warning isn’t clear enough. You need to be aware of certain technical details to understand what it’s telling you; there is ample precedent for error messages spelling out such details when they are expected to be faced by non-technical users. This might be a case where that’s a good idea.
Well, after all the trouble you got in already, I hope that you already did a backup of your data (not as in Syncthing version, separately) before doing any more debugging/restoring (incidentally, you should do that anyway).
That error comes up when Syncthing got an update from another device, telling it to delete that directory. However there is still valid content therein, so it doesn’t delete it.
I suggest you stop Syncthing immediately, make sure that have all the files you want on both (all?) the devices (without Syncthing), then carefully reintroduce Syncthing. Part of being careful when doing that is for example setting the folders as send-only to see what differences there are before they get synced.