Apt-get: Network is unreachable
 

I am on a Kubuntu behind a proxy and I'm trying to make sudo apt-get update. The apt-get saysThe problem is that this error is really weird, because:
1) I configured proxy in system settings.
2) I suppose, that apt-get can't handle this settings, so I tried to configure proxy for an apt-get through an export as follows:
And when it doesn't worked, I tried this:
But nothing get worked :(

Hmm, I found a strange thing: the apt-get works through a netbook with an installed Ubuntu. So I tried to copy sources.list(though it's pretty the same, the only difference is the release name: precise VS saucy), but it doesn't worked anyway.
I hope I'm close... «The Truth Is Out There» =)

Aha! Through comparing tcpdump output on a netbook and PC, I found a next hint: all output of the netbook goes through a 3128 port -- it's a proxy. On a desktop that's also true for webpages, but not for an apt-get.
This also means that export http_proxy= doesn't work, although it should, so an apt-get is buggy.
Anyway, despite the broken apt-get there's sure a way to get it work, as apt-get on a netbook working without dark magic with an "export".

apt-get has its own configuration file for proxy settings: http://www.debian-administration.org/articles/177

This is true, but this is a permanent settings. They wrote in a manual that I can set a temporary proxy settings through an export and they're lying as you're can see =) I don't think that a permanent settings going to work, if a temporary doesn't.

Finally I get it to work! Tell me, do anybody see which one of two lines below is going to guide me to the success?
Yes, you're right, the second one is wrong. To be precicer it's just unnecessary line, it looks like a ghost: it was mentioned everywhere but doesn't seems that something depends on this line.
The solution was to add the line http_proxy="http://10.5.57.177:3128" to the /etc/environment/. When an apt-get launched it's parses this file and this line too.
This blog post very helped me, thank him very much!