The first problem was with apt-cacher-ng. Well, actually it was two problems. The first involves an apparent difference between how Ubuntu and Debian configure their apt clients to use a proxy.
On Ubuntu I have always used /etc/apt/apt.conf with a single line pointing to my proxy like so;
Acquire::http { Proxy "http://apt:3142"; };This didn't seem to work with Debian clients, the fix is to put the same line into a file at /etc/apt/apt.conf.d/01proxy.
Actually you can call the file anything you like, even "apt.conf" but naming the file like this fits in with normal Debian conventions better, which can't be a bad thing.
The second issue I had was with Ubuntu clients using the apt-cacher-ng proxy installed on a Debian server.
I kept getting "404 Not Found" errors every time I did an apt-get update on the (lucid) clients.
Google was no help. There were a few people who were having the same problem but no answers.
Eventually I found the issue myself. There is a file in the apt-cacher-ng directory that has an error. To fix the problem you edit this file;
vi /etc/apt-cacher-ng/backends_ubuntuand change the line so it says something like this;
http://au.archive.ubuntu.com/ubuntu/Of course you should change it to something more local to where you are. The key here is that on my system the trailing /ubuntu/ was missing and this was causing the 404 errors.
