From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alain Bourgeois <alain.bourgeois@zetes.com>
cc: pgsql-docs@lists.postgresql.org
Subject: Re: pg_upgrade -c cannot be run if old cluster is running
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Comments: In-reply-to Alain Bourgeois <alain.bourgeois@zetes.com>
	message dated "Thu, 05 Sep 2024 14:32:32 -0000"
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Date: Thu, 05 Sep 2024 10:57:04 -0400
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Alain Bourgeois <alain.bourgeois@zetes.com> writes:
> I confirm copyig config to data dir and specifying data dir works
> /usr/pgsql-15/bin/pg_upgrade --check -b /usr/pgsql-10/bin/ -B /usr/pgsql=
-15/bin -d /mnt/pgdata/pgdir -D /mnt/pgdata/pgdirbc15 --check

Hm.  On second look, there is code in there that intends to deal
with -d pointing at a configuration-only directory, and it seems
to work for me:

$ pg_upgrade --check -d /home/postgres/version10/config ...etc...
Finding the real data directory for the source cluster      ok
Performing Consistency Checks on Old Live Server
------------------------------------------------
Checking cluster versions                                   ok
Checking database user is the install user                  ok
Checking database connection settings                       ok
...

The lack of any comment about "Finding the real data directory"
in your output is suspicious.  I notice that the code that
does this has a short-circuit case that perhaps could get fooled:

    /* If PG_VERSION exists, it can't be a config-only dir */
    snprintf(filename, sizeof(filename), "%s/PG_VERSION", cluster->pgconfi=
g);
    if ((fp =3D fopen(filename, "r")) !=3D NULL)
    {
        fclose(fp);
        return;
    }

Do you have a PG_VERSION file in /var/lib/pgsql/10/data?
If so, why?

			regards, tom lane