Unable to setup Postgres in Nix-Shell - postgresql

Question

I'm working on a Phoenix/Elixir project which is managed using nix-shell. I'm having issues regarding postgres setup.
I'm starting server using pg_ctl -D $PGDATA start and it outputs as:
pg_ctl: another server might be running; trying to start server anyway
waiting for server to start....2021-09-01 19:19:00.780 PKT [72367] LOG: listening on IPv4 address "127.0.0.1", port 5432
2021-09-01 19:19:00.784 PKT [72367] LOG: listening on Unix socket "/tmp/.s.PGSQL.5432"
2021-09-01 19:19:00.806 PKT [72369] LOG: database system was interrupted; last known up at 2021-09-01 19:14:57 PKT
2021-09-01 19:19:00.848 PKT [72369] LOG: database system was not properly shut down; automatic recovery in progress
2021-09-01 19:19:00.849 PKT [72369] LOG: redo starts at 0/16D84A0
2021-09-01 19:19:00.849 PKT [72369] LOG: invalid record length at 0/16D8580: wanted 24, got 0
2021-09-01 19:19:00.849 PKT [72369] LOG: redo done at 0/16D8548
2021-09-01 19:19:00.862 PKT [72367] LOG: database system is ready to accept connections
done
server started
when I execute createuser postgres --createdb --echo in nix-shell envoirnment it produces following error even though the run directory exists.
createuser: could not connect to database template1: could not connect to server: No such file or directory
Is the server running locally and accepting
connections on Unix domain socket "/run/postgresql/.s.PGSQL.5432"?
No other postgres instance is running.
In pg_hba.conf auth method is set to trust.
unix_socket_directories is set to /tmp.
shell.nix looks something like
{ pkgs ? import <nixpkgs> {} }:
with pkgs;
let
inherit (lib) optional optionals;
elixir = beam.packages.erlangR22.elixir_1_10;
postgresql = postgresql_11;
in
mkShell {
buildInputs = [
ps
elixir
coreutils
which
git
postgresql
redis
doxygen
mongodb-tools
redis-dump
(python37.withPackages(ps: with ps; [ credstash awscli ]))
cmake
nix-prefetch-git
zlib
jq
teleport
]);
# Fix GLIBC Locale
LOCALE_ARCHIVE = lib.optionalString stdenv.isLinux
"${pkgs.glibcLocales}/lib/locale/locale-archive";
LANG = "en_US.UTF-8";
# Put the PostgreSQL and Redis databases in the project diretory.
PGDATA="./.db/postgres";
RDDATA="./.db/redis";
shellHook = ''
ERL_INCLUDE_PATH="${erlangR22}/lib/erlang/usr/include";
}
I totally a noob to Nix and have no idea how to get it working.
Any help would be appreciated, thanks.

Answer 1

You have to tell createuser to connect via the socket in /tmp:
createuser -h /tmp -U postgres --createdb --echo newuser

Answer 2

You've set a custom path in the postgres config, so you probably also need to specify that with pqsl / createuser. In other words createuser -h /tmp/ ....