At work I have an ubuntu desktop behind a proxy. I configured my proxy as follows: Under Settings > Network > Network proxy : Method set to "automatic", set a URL and applied system wide.
This enabled access to the internet (eg firefox), except for apt-get. To get apt-get working, I followed these instructions, specifically under "Setting up apt-get to use a http-proxy > APT configuration file method". With these settings I can install packages (eg thunderbird), but I have a problem when I add a new repository:
W: GPG error: http://ppa.launchpad.net vivid Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 737F9811F93FF666
I'm assuming this has something to do with the proxy, but I can't seem to fix it with any method/tip I have found online so far. For example, adding the proxy settings as environment variables (
export https_proxy=...) and then using
sudo -E did not help.