Comment 0 for bug 326718

Binary package hint: apt

apt-get seems to get into trouble resolving DNS names when other programs, including nslookup and dig, Firefox, and ping are unaffected.

This results in warnings like:
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/jaunty-security/Release.gpg Could not resolve 'security.ubuntu.com'
...and obviously makes it difficult to use apt!

In researching the problem, people seem fond of blaming nsswitch/mdns/avahi, specific DNS servers or the phase of the moon. However, there is clearly some real bug (or unexpected behavior) here.

Not aiding my attempts to debug the issue: when I attempt to use tcpdump to monitor the DNS lookups, e.g. with `sudo tcpdump -ni eth0 -vvvv > dump`, it often goes away! Then, without tcpdump running, it's back! Perhaps this is actually a kernel bug of some flavor?

I am having a bit of trouble following the actual lookups (and results) in the strace output [produced via `sudo strace -v -s4096 apt-get update`] attached. Can someone have a look at what is going on there? At the time that was taken:

resolv.conf was/is:

# Generated by NetworkManager
domain gateway.2wire.net
search gateway.2wire.net
nameserver 172.16.0.1

[This is a 2Wire Homeportal gateway, which has some sort of DNS cache/DNS proxy in it -- at least enough to let you address the device by the hostname 'homeportal'. I've never had any trouble running lookups through it on numerous other Linux, BSD, and Windows systems.]

nsswitch.conf was:

# /etc/nsswitch.conf
#
# Example configuration of GNU Name Service Switch functionality.
# If you have the `glibc-doc-reference' and `info' packages installed, try:
# `info libc "Name Service Switch"' for information about this file.

passwd: compat
group: compat
shadow: compat

#hosts: files mdns4_minimal [NOTFOUND=continue] dns mdns4
hosts: files dns
networks: files

protocols: db files
services: db files
ethers: db files
rpc: db files

netgroup: nis

[The behavior was first observed with Jaunty's default nsswitch.conf; I first tried the [NOTFOUND=continue] edit for mdns lookups commented above, then chopped it down to only files and dns, and have since chopped it down to *only* "dns." Mysteriously, chopping it down to only "dns" has "switched the bug around" -- now apt-get can resolve us.archive.ubuntu.com but security.ubuntu.com fails. Unless I'm running tcpdump on the interface - then everything works!?]