> The backup will include all files in the data directory and tablespaces, including the configuration files and any additional files placed in the directory by third parties, except certain temporary files managed by PostgreSQL.
It's also unclear why it's failing when it does try to read it, since the file has the same permissions and security context that should allow the instance to read it (even though the backup really shouldn’t need to read it).
Understandable, but not a pg_basebackup bug that it is being told it lacks permission. But I suspect there is file locking involved and it isn't a file permission problem.
