When you use the generate option of the docker image to generate a config file, there is no way to tell it where you want to put the media store etc, and it uses /.

Then, when you try to start synapse using the generated config, you get:

PermissionError: [Errno 13] Permission denied: '/media_store'

We should probably use /data by default (and recommend that a volume is mounted there), with an env var to allow you override the path. We also need to chown it so that synapse can write to it.

A workaround is:

• Add -w /data to the generate commandline, then
• docker run <volume_options> --entrypoint=chown matrixdotorg/synapse:latest 901 /data