Re: pg_upgrade from 17.10 to 18.4 on Ubuntu fails: Finding the real data directory for the target cluster sh: 1: (null)/postgres: not found

Hi,

On Wed, Aug 12, 2026 at 12:50:57PM +0200, Holger Jakobs wrote:
> Today a pg_upgrade failed with this awkward message:
>
> Finding the real data directory for the source cluster        ok
> Finding the real data directory for the target cluster        sh: 1:
> (null)/postgres: not found

What was the exact command line you used?

> Obviously, cmd should contain the path of the oldbin directory, which is to
> be derived from the path of the pg_upgrade being called.

Are you saying you ran the 17 pg_update binary? I am not sure that is
supported/supposed to work, one should use the pg_upgrade binary from
the newer Postgres version (unless I misunderstood you).

Still, the error isn't great and should be improved / this case should
be caught earlier in pre-flight checks probably.

Michael