This hook starts a PostgreSQL server during the checkPhase. Example:

{ stdenv, postgresql, postgresqlTestHook }:
stdenv.mkDerivation {

  # ...

  nativeCheckInputs = [

If you use a custom checkPhase, remember to add the runHook calls:

  checkPhase ''
    runHook preCheck

    # ... your tests

    runHook postCheck


The hook logic will read a number of variables and set them to a default value if unset or empty.

Exported variables:

  • PGDATA: location of server files.
  • PGHOST: location of UNIX domain socket directory; the default host in a connection string.
  • PGUSER: user to create / log in with, default: test_user.
  • PGDATABASE: database name, default: test_db.

Bash-only variables:

  • postgresqlTestUserOptions: SQL options to use when creating the $PGUSER role, default: "LOGIN". Example: "LOGIN SUPERUSER"
  • postgresqlTestSetupSQL: SQL commands to run as database administrator after startup, default: statements that create $PGUSER and $PGDATABASE.
  • postgresqlTestSetupCommands: bash commands to run after database start, defaults to running $postgresqlTestSetupSQL as database administrator.
  • postgresqlEnableTCP: set to 1 to enable TCP listening. Flaky; not recommended.
  • postgresqlStartCommands: defaults to pg_ctl start.


A number of additional hooks are ran in postgresqlTestHook

  • postgresqlTestSetupPost: ran after postgresql has been set up.

TCP and the Nix sandbox

postgresqlEnableTCP relies on network sandboxing, which is not available on macOS and some custom Nix installations, resulting in flaky tests. For this reason, it is disabled by default.

The preferred solution is to make the test suite use a UNIX domain socket connection. This is the default behavior when no host connection parameter is provided. Some test suites hardcode a value for host though, so a patch may be required. If you can upstream the patch, you can make host default to the PGHOST environment variable when set. Otherwise, you can patch it locally to omit the host connection string parameter altogether.


The error libpq: failed (could not receive data from server: Connection refused is generally an indication that the test suite is trying to connect through TCP.