Empty error on starting almost-default PostgreSQL
Fixed. First I changed the owner of /vol/postgres to postgres (after comments on the question). This resulted in the following understandable error:
* The PostgreSQL server failed to start. Please check the log output:
2012-05-25 07:50:13 GMT FATAL: data directory "/vol/postgres" has group or world access
2012-05-25 07:50:13 GMT DETAIL: Permissions should be u=rwx (0700).
So I did what it says and now it starts.