If Syncthing says a folder synced but the files appear inside Docker overlay2, the destination path was not actually mounted into the container. That is the key technical clue in this June 2025 thread: Syncthing wrote into its disposable container filesystem because the expected FileDrop bind mount was missing from docker inspect.
The thread was never solved on the original ZimaOS install—the user eventually moved to Debian/CasaOS—so the article should use the diagnosis without pretending the original configuration was repaired.
The UI Mapping and the Running Container Did Not Match
The user’s ZimaOS app form showed a FileDrop mapping, yet docker inspect big-bear-syncthing did not list that mount. That mismatch explains why Syncthing created /FileDrop inside its own writable container layer.
overlay2 Is a Warning Sign for Persistent Sync Data
Files under .docker/overlay2/.../diff/FileDrop are inside the container filesystem. Recreating or replacing the container can remove that layer. Synced payloads should live on a persistent bind mount or named volume.
The current ZimaOS Syncthing guide now documents a supported setup flow including folder path, PUID and PGID.
/DATA and /media/ZimaOS-HD Were the Same Storage Root
/media/ZimaOS-HD and /DATA referred to the same ZimaOS storage root in that layout. Source: IceWhale Community Forum.IceWhale clarified that /media/ZimaOS-HD pointed to /DATA on that system. The path alias itself was therefore not the main explanation for files landing in overlay2.
The real question is whether the exact host folder appears in the container’s Mounts list with the expected container-side target.
Use Current Syncthing Folder Rules
The current official guide advises using a dedicated Syncthing folder path, setting correct PUID/PGID values, and creating destination folder paths through Syncthing rather than manually through the ZimaOS file browser for this workflow.
The Syncthing deployment guide provides the broader storage layout context.
Bottom Line
If synced files land in Docker overlay2, stop debugging Syncthing peer connectivity and inspect the container mounts. Make sure the destination host folder is really mounted, use the container-side path in Syncthing, match PUID/PGID to writable host ownership, and recreate the app if the saved UI definition does not match the running container.
