Running postgres with shepherd as user-level service?

[Carlo Holl <mail@carlo.red>]

Hello Guix!

I'm struggling to find the right incantation to start a postgresql service with
shepherd outside of a system context.

Suppose the following snippet (postgres.scm):

(use-modules (gnu services)              (gnu packages databases)              
(gnu services databases))

(define pg-service   (service postgresql-service-type     
(postgresql-configuration       (postgresql postgresql)
       (data-directory "path-to-data-dir"))))

(register-services pg-service)
(start pg-service)


If I run the above with 'herd load root postgres.scm', I get:

     Loading postgres.scm.
     herd: exception caught while executing 'load' on service 'root':
     In procedure fport_write: Input/output error

Firstly, I'm not sure this is the right approach. Are the services defined in
say (gnu services databases) supposed to be run outside of system config context?

Secondly, I don't know how to go about diagnosing the issue since I'm not given
a stack trace and I don't know where to get a more detailed log of the 
failure. The shepherd log file just shows 'Loading postgres.scm' for 
every invocation of
the herd command.

A point in the right direction would be greatly appreciated.

-Carlo