How to analyze a "[Waiting for headers]" problem during "apt-get update"?

Question

sudo apt-get update sometimes becomes stucked:

...
99% [Waiting for headers]

This seems to be a common problem and can have several reasons. For example, on one machine, it was caused because I used a bad proxy server configuration.

Is there a way to systematically analyze the problem? It looked at the man apt-get but could not find any option that provides more information to isolate the problem. Are there any tools besides apt-get that I can use to get more insights?

Solution 1

I was able to fix it. http://debian.sur5r.net/i3/ (quantal, universe) did not respond. After disabling it, apt-get update succeeds.

Tips for the next one that runs into this problem:

1. Start synaptic and disable sources until Reload no longer hangs. Especially, 3rd party sources seem to be candidates.
2. Reactive your sources until you hit the one that causes problems.

synaptic is great for diagnostics. When Reload hangs and you abort it, it prints out the current repository. In my case, it was exactly the bad one:

Failed to fetch http://debian.sur5r.net/i3/dists/quantal/InRelease  
Some index files failed to download. They have been ignored, or old ones used instead.

Solution 2

Better still, just do:

apt-get -o Debug::Acquire::http=true update

Comments

[Flimm]

This is a network connectivity problem, and is not specific to apt-get.

[Philipp Claßen]

@Flimm My internet connection seems to be fine. I have no problem besides apt-get update. Installing new packages via apt-get install also worked. You may be right that apt-get does not cause the problem but at least for me it is some kind of blackbox. My question is what can I do isolate the problem?

[Mr. Robot]

Check out this link: askubuntu.com/questions/156650/…

[Philipp Claßen]

@Mukund Thanks, that helped me to fix the problem. See my answer below.

[xerostomus]

I solved this problem simply by unpluging the wifi connection and connecting my PC directly via a cable. So problem was somewhere in my wifi routers (OpenWrt). Unfortunatelly I am unable diagnose where... :-(

[Admin]

Are you sure that you wouldn't see something similar to "Failed to fetch debian.sur5r.net/i3/dists/quantal/InRelease Some index files failed to download. They have been ignored, or old ones used instead." even using plain apt-get?

[Philipp Claßen]

@vasa1 No, it just hangs forever. When you abort it by pressing ctrl-c, it does not print anything before it quits.

[XtraSimplicity]

This is great! It helped to show that there was actually a problem with my firewall's HTTP proxy -- which I had forgotten I even had! :)