/etc/apt/apt.conf.d/90squid is in debian-edu-config 1.818+deb8u2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 | // Avoid Squid handing out corrupt packages, solves Skolelinux bug
// #1419.
Acquire::http::Pipeline-Depth 0;
|