I have a server VM running Ubuntu 14.04. It mostly just runs apt-cacher-ng, which I suspect is running into its limit on open files. What's the proper way to increase this limit? I know there's the limit in /etc/security/limits.conf, but I've read elsewhere that doesn't apply! I've also read about "stanzas" for "Upstart" in Ubuntu, but I have no idea where to look for the right place to put that. I'm expecting something like