SOLVED - The correct way is like this: ssh into the NAS as root and edit the following file /usr/local/btsync/var/sync.conf { "device_name": "SynologyNAS", "storage_path" : "/usr/local/btsync/var", "pid_file" : "/usr/local/btsync/var/syncapp.pid", "webui" : { "listen" : "0.0.0.0:8888", "login" : "mainUser", "password" : "mainPassword", "login" : "workUser", "password" : "workPassword" } }With this the BTsync service can successfully be restarted. Then there was one more permission (in the properties of "shared folders") to be set appropriately and now it seems to work. I will test it now, but looks good.