How to waste hours with computer problems

I just wasted several hours with yet another computer problem.

Some Background: We are using a Ubuntu based server which runs Samba as a file server for Windows computers. It also is a local name server and mail server. Yesterday it was that time again that I had to reboot it because of some Linux kernel update. I waited until everybody had gone home, the box rebooted, everything seemed fine.

Until this morning: The first problem was that there was no e-mail telling me about the automatic backup last night. Then my web browser (which uses a proxy running on the server) did not work. Also there were suspiciously no spam emails.

So I investigated and found that the name service did not work, but only on the server itself. All clients could use the service and got the expected answers. But fetchmail and lots of daemons running on the server itself did not work.

Many minutes later I put our Internet provider’s into


and name resolution started to work again for external addresses. E-mail was still broken, and I became desperate so I went to hoping that somebody much more knowledgeable than me might know this problem.

I got quite a few hints on what to check but no luck.

The solution was absolutely unexpected (at least to me):
The loopback interface was not started!

Starting it with …

ifup -v lo

… fixed the problem.