pg_basebackup copies the data directory permission mode from the
upstream server. But it doesn't copy the ownership. So if say the
upstream server allows group access and things are owned by
postgres:postgres, and I want to make a copy for local development and
make a backup into a directory owned by peter:staff without group
access, then it would be inappropriate for pg_basebackup to change the
permissions on that directory.
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Peter Eisentraut http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services