Hi Gary,

On Tue, Nov 10 2020, Gary Johnson wrote:
> It's been a week since my original post requesting assistance 
> with getting Postgresql and PostGIS to work together correctly, 
> but unfortunately I still haven't received any help with this 
> issue.
> ...
> Does anyone know how this code works or how to fix this issue?

I didn't respond initially because I don't have any specialist 
knowledge about this. I had some free time today, so I did a bit 
of an investigation and I think I've figured out what's gone wrong 
for you here.

In your original email you gave this definition for postgresql-13:

    (define-public postgresql-13
      (package
       (inherit postgresql)
       (name "postgresql")
       (version "13.0")
       (source (origin
                (method url-fetch)
                (uri (string-append 
                "https://ftp.postgresql.org/pub/source/v"
                                    version "/postgresql-" version 
                                    ".tar.bz2"))
                (sha256
                 (base32
                  "15i2b7m9a9430idqdgvrcyx66cpxz0v2d81nfqcm8ss3inz51rw0"))))))

However, this is missing one important line from the original 
postgresql definition, which applies a patch to the source:

    (patches (search-patches 
    "postgresql-disable-resolve_symlinks.patch"))

This patch changes how Postgres treats symlinks, which Guix uses 
extensively. If we add this patch the definition of postgresql-13 
we should get:

    (define-public postgresql-13
      (package
       (inherit postgresql)
       (name "postgresql")
       (version "13.0")
       (source (origin
                (method url-fetch)
                (uri (string-append 
                "https://ftp.postgresql.org/pub/source/v"
                                    version "/postgresql-" version 
                                    ".tar.bz2"))
                (sha256
                 (base32
                  "15i2b7m9a9430idqdgvrcyx66cpxz0v2d81nfqcm8ss3inz51rw0"))
                (patches (search-patches 
                "postgresql-disable-resolve_symlinks.patch"))))))

I put this into a system definition (a bit hacky, but attached) 
and built it using "guix system vm helping-gary.scm". Logging into 
the system as root I was able to run this successfully:

    sudo -u postgres psql -c 'create extension postgis'

I hope that helps!

Carlo