Prevent pg_basebackup running as root

Hi

We encountered an unfortunate case of $SUBJECT the other day where it
would have been preferable to catch the error before rather than after
pg_basebackup ran.

I can't think of any practical reason why pg_basebackup would ever need to
be run as root; we disallow that for initdb, pg_ctl and pg_upgrade, so it
seems reasonable to do the same for pg_basebackup. Trivial patch attached,
which as with the other cases will allow only the --help/--version options
to be executed as root, otherwise nothing else.

The patch doesn't update the pg_basebackup documentation page; we don't
mention it in the pg_ctl and pg_upgrade pages either and it doesn't seem
particularly important to mention it explicitly.

I'll add this to the March CF.

Regards

Ian Barwick

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Ian Barwick https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services