Why does add-apt-repository now fail to retrieve keys behind my proxy server, but I can update package lists and manually receive the keys?
75879
How do I get add-apt-repository to work through a proxy?
113145
What does 'apt-get install update' do?
108510
apt-get update very slow, stuck at "Waiting for headers"
34069
Why am I getting authentication errors for packages from an Ubuntu repository?
54998
What does "apt-get install !!" do and how to make it work?
19565
Restore default apt repositories in sources.list from command line
57717
Proxy Blocking apt-get, Allowing wget/curl
157904
error 503: service unavailable when using apt-get update behind proxy
12968
What should I do when the GETDEB repository is down?
66285
Package repository down, how to relocate?
155179
How to get apt-cacher-ng to download AND cache packages from Apt HTTPS repositories?
96145
Cannot Add PPA Behind Proxy Ubuntu 14.04
143747
How do I enable the "backports" repository?
21184
Running "sudo apt-get update" returns connection errors
121462
Fixing a broken packet system (apt-get)
125645
Ubuntu 12.04 APT Proxy?
113442
apt-get not working on Ubuntu 16.04, problems with kernel packages