This question has been marked as a duplicate but there is no link to original quetion:
Why is this so? And what can be done for such questions?
The link was probably mistakingly removed after an edit to the question. You can find the duplicate in the question's revisions.
I've re-added the duplicate manually to the question for future vsitors.
You still have the
Linked on the right-hand panel. This specific question is probably duplicate of 'apt-get' does not work with Proxy.