I had similar issue, sometimes the pg directories somehow don't get created correctly so I've end up creating them manually by doing:
```
$ pg_ctl -D /usr/local/share/c3/postgres/data start
```
This will fail with some random logs like
```
2019-08-05 14:18:50.120 PDT [12307] LOG:  could not open directory "pg_snapshots": No such file or directory
```
So you need to manually create this `pg_snapshots` folder under `/usr/local/share/c3/postgres/data`.

Doing this iteratively until all needed files are created solved the problem for me.