/usr/share/postgresql/10/extension/refint.control is in postgresql-10 10.3-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 | # refint extension
comment = 'functions for implementing referential integrity (obsolete)'
default_version = '1.0'
module_pathname = '$libdir/refint'
relocatable = true
|