Yes, I am writing a tiny app to test that a BLE device works properly, and Elixir is a great language to get things done quickly.

Thanks for the tip, I’ll check muontrap and see what I can do from that.

In your Elixir application’s start function, call File.mkdir("/run/dbus").

Here’s the longer answer:

The default Nerves configuration mounts several different filesystems. The main one, /, is read-only and contains OTP, Linux programs, and your Elixir application and all of its dependencies. You can add to that one via the rootfs_overlay. However, some directories are made writable at runtime. Anything placed in those directories at compile-time isn’t accessible at runtime and that’s what you’re running into. Examples are the /tmp, /dev, /run, and /root directories. In the case of /tmp, /dev, and /run, Nerves mounts small in-memory filesystems. They’ll lose their contents on reboots so if you’re going to create a directory in them, you need to do it each boot. This is generally desirable since if something gets messed up in them, a reboot returns you to a good state. In the case of /root, a writable filesystem is mounted there so that iex prompt history and other things survive reboots.

As a general rule of thumb, I try to avoid using the rootfs_overlay feature. Usually Linux programs have a way to tell them where their configuration files are. That lets me put the config file in a more convenient location - like in my OTP application’s priv directory and tell it to read it from there. If programs need to write data, I can redirect them some place on /data, etc. Of course, it’s nice to see things work once before moving paths around, so this might be something to consider after the dust settles.

Great to see some bluetooth love.

You are on the right track. You will have to start dbus and bluetoothd manually as part of your supervision tree. Check out muontrap