/usr/share/postgresql/10/extension/pg_buffercache.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 | # pg_buffercache extension
comment = 'examine the shared buffer cache'
default_version = '1.3'
module_pathname = '$libdir/pg_buffercache'
relocatable = true
|