Syncthing running in Docker compose: Mapping error

forum.openmediavault.org/wsc/index.php?attachment/41277/I followed the instructions from here: https://wiki.omv-extras.org/doku.php?id=omv7:docker_in_omv to set SYNCTHING up in Docker Compose. SYNCTHINg within Docker is starting up as expected.

I can also add a device [phone] to the server [status=connected]. However, when I try to synchronize the phone to the SYNCTHING server I am getting an error:

2025-09-03 15:02:33: Failed to create folder marker (folder.label=mash_SamsungS10/DCIM folder.id=jha6c-ncqpw folder.type=sendreceive error="mkdir /run/s6-rc:s6-rc-init:JPHjCl/servicedirs/svc-syncthing/.stfolder: permission denied" log.pkg=model)


2025-09-03 15:02:33: Failed initial scan (error="folder marker missing (this indicates potential data loss, search docs/forum to get information about how to proceed)" folder.label=mash_SamsungS10/DCIM folder.id=jha6c-ncqpw folder.type=sendreceive log.pkg=model)

After hours of trying every option I can think of I am confuddled.

Here my docker files:

# Date: 2025-06-01
# https://hub.docker.com/r/linuxserver/syncthing
services:
syncthing:
image: lscr.io/linuxserver/syncthing:latest
container_name: syncthing
hostname: syncthing3 #optional
environment:
- PUID=${APPUSER_PUID}
- PGID=${APPUSER_PGID}
- TZ=${TIME_ZONE_VALUE}
volumes:
- ${PATH_TO_APPDATA}/syncthing/config:/config
- ${PATH_TO_SYNCDATA}/mash/SAMSUNG/DCIM:/sync           # SAMSUNG phone mash - Folder DCIM
ports:
- 8384:8384
- 22000:22000/tcp
- 22000:22000/udp
- 21027:21027/udp
restart: unless-stopped

# THE FOLLOWING VARIABLES CAN BE USED IN ANY COMPOSE FILE
# THEIR VALUE WILL BE REPLACED BY THE VALUE ASSIGNED HERE
# YOU CAN ADD AS MANY VARIABLES AS YOU NEED
#
#
# Customize the PID and GID value of your appuser user.
# You can see it in the OMV GUI in the USERS > USERS tab
#
APPUSER_PUID=1001
APPUSER_PGID=100
#
# Customize your time zone value.
# You can see it in the OMV GUI in the SYSTEM > DATE & TIME tab
#
TIME_ZONE_VALUE=US/Mountain
#
# In this file you can define how many paths you need for different compose files.
# The following are examples corresponding to the example system in the Docker on OMV document on the omv-extras wiki.
# Customize the values according to your system configuration.
#
PATH_TO_APPDATA=/srv/dev-disk-by-uuid-84aa9dee-1a67-4f44-b67d-a3ac9546f438/appdata
PATH_TO_SYNCDATA=/srv/dev-disk-by-uuid-84aa9dee-1a67-4f44-b67d-a3ac9546f438/sync

User 'appuser' exists and has r/w access to shared folder 'appdata' and 'sync' [as defined in the YAML config files.

What FOLDER PATH do I have to add to the SYNCTHING when trying to add a folder from the phone [see attachment]?

Any ideas/pointers highly appreciated.

Thanks for the reply, that was my original config based on my understanding of docker and its configuration.

Could there be some lingering/remaining issues from prior attempts with a wrong FOLDER PATH [path based on filesystem (/srv/dev-disk-by-uuid-84aa9dee-1a67-4f44-b67d-a3ac9546f438/sync)]?

Well, spent a few hours on the problem... thought I made some progress but the mess became just a little bigger:

On filesystem level, the OMV shared folder belonged to root:????. Changed that to appuser:users. Restarted the container . If I remember correctly it created the folder underneath but with the wrong owner:user. I changed the permissions to appuser:users for this folder and syncgthing was able to perform a sync [yeah]. All files belong to appuser:users as expected.

Restarting the container however, results in an error message in SYNCTHING:

2025-09-07 17:01:20: Failed initial scan (error="folder marker missing (this indicates potential data loss, search docs/forum to get information about how to proceed)" folder.label=mash_SamsungS10/DCIM folder.id=jha6c-ncqpw folder.type=sendreceive log.pkg=model)              

Any ideas how to proceed?

Thanks