Using SyncThing to synchronize the settings of another app: 'folder path missing'

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1

With Syncthing, I was able to successfully set up synchronisation between a NAS (QNAP TS-431P) and a smartphone (Android 15).

Now, a PC (ZOTAC ZBOX CI645) running openSUSE Tumbleweed should be added. I installed the SyncThingy app (v0.8) as a Flatpak from FlatHub. SyncThing should be used here to synchronise the settings of an app called FreeTube. The FreeTube app is also installed as a Flatpak from FlatHub. Contrary to expectations, however, synchronisation does not work on openSUSE Tumbleweed. The error ā€˜folder path missingā€™ is reported, although the set folder path exists. If you copy the folder path from the SyncThing web interface and paste it into a file manager, the folder path is opened without any problems and you can see its contents.

Log:

2025-04-22 20:22:08 My ID: 5NXHME3-RJQTKH2-PC2VII7-C2GGBRO-UNVN4OJ-PQLZKBQ-EXBQURV-CICLDA6
2025-04-22 20:22:08 Hashing performance is 1126.00 MB/s
2025-04-22 20:22:08 Overall send rate is unlimited, receive rate is unlimited
2025-04-22 20:22:08 Relay listener (dynamic+https://relays.syncthing.net/endpoint) starting
2025-04-22 20:22:08 Using discovery mechanism: global discovery server https://discovery-lookup.syncthing.net/v2/?noannounce
2025-04-22 20:22:08 Using discovery mechanism: global discovery server https://discovery-announce-v4.syncthing.net/v2/?nolookup
2025-04-22 20:22:08 Using discovery mechanism: global discovery server https://discovery-announce-v6.syncthing.net/v2/?nolookup
2025-04-22 20:22:08 Using discovery mechanism: IPv4 local broadcast discovery on port 21027
2025-04-22 20:22:08 Using discovery mechanism: IPv6 local multicast discovery on address [ff12::8384]:21027
2025-04-22 20:22:08 Ready to synchronize "Settings/FreeTube" (Settings/FreeTube) (sendreceive)
2025-04-22 20:22:08 ...
2025-04-22 20:22:08 Failed initial scan of sendreceive folder "Settings/FreeTube" (Settings/FreeTube)
2025-04-22 20:22:08 Error on folder "Settings/FreeTube" (Settings/FreeTube): folder path missing
2025-04-22 20:22:08 Ready to synchronize "Default Folder" (default) (sendreceive)
2025-04-22 20:22:08 QUIC listener ([::]:22000) starting
2025-04-22 20:22:08 TCP listener ([::]:22000) starting
2025-04-22 20:22:08 Completed initial scan of sendreceive folder "Default Folder" (default)
2025-04-22 20:22:08 GUI and API listening on 127.0.0.1:8384
2025-04-22 20:22:08 Access the GUI via the following URL: http://127.0.0.1:8384/
2025-04-22 20:22:08 My name is "ZOTAC ZBOX CI645 nano"
2025-04-22 20:22:08 Device 4AN7SHX-I65A5JU-L4PZJMK-Z7YSKRV-PRRVTI7-DQPF52C-O57VX72-IDPLXAS is "QNAP TS-431P" at [dynamic]
2025-04-22 20:22:08 Established secure connection to 4AN7SHX at 192.168.178.59:22000-192.168.178.76:22000/tcp-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256/LAN-P10-61OMS6TQ5AHTU51UM9J47CEAJQ
2025-04-22 20:22:08 Device 4AN7SHX client is "syncthing v1.28.1" named "QNAP TS-431P" at 192.168.178.59:22000-192.168.178.76:22000/tcp-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256/LAN-P10-61OMS6TQ5AHTU51UM9J47CEAJQ
2025-04-22 20:22:22 Joined relay relay://45.132.245.205:22067
2025-04-22 20:22:38 Failed to acquire [::]:22000/TCP open port on NAT-PMP@192.168.178.1: getting new lease on NAT-PMP@192.168.178.1 (external port 33874 -> internal port 22000): unexpected result size 12, expected 16
2025-04-22 20:22:38 Detected 1 NAT service
2025-04-22 20:52:10 Sent usage report (version 3)
2025-04-22 20:53:08 Failed to acquire [::]:22000/TCP open port on NAT-PMP@192.168.178.1: getting new lease on NAT-PMP@192.168.178.1 (external port 33874 -> internal port 22000): unexpected result size 12, expected 16
2

The desktop file manager is able to access any files belonging to a Flatpak app, but not the other way around.

Flatpak apps are basically isolated islands. If you were to try and point Syncthing at ~/Documents, itā€™d result in the same ā€œfolder path missingā€ error.

A Flatpak app touching the files of another Flatpak app is also blocked by default ā€“ e.g. it prevents a tainted network file transfer app from grabbing the database for a password manager app.

See: https://docs.flatpak.org/en/latest/sandbox-permissions.html

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