when /etc/hosts doesn't exist, apt fails to resolve hostnames using libc6

[LaMont Jones]

the lack of /etc/hosts should not prevent a host with /etc/resolv.conf from resolving hostnames.

Interestingly, ping and a few other applications resolve hosts just fine with no /etc/hosts on the system, apt does not.

lamont

[Steve Langasek (vorlon)]

blocker for karmic alpha-4, since it breaks livefs builds.

[Matthias Klose (doko)]

$ sudo whoami
sudo: unable to resolve host timbuktu
root

[to be removed (liw)]

ping, host, nslookup, and dig, at least, do DNS lookups only, and do not use the (default) libc resolver.

[to be removed (liw)]

apt exhibits the problem. wget doesn't.

[to be removed (liw)]

The attached file provides a test case. Compile, then run it as follows: "./a.out ubuntu.com". If /etc/hosts exists, it should print "ubuntu.com 0". If it does not exist, it should print "ubuntu.com -11".

[to be removed (liw)]

http://www.eglibc.org/archives/patches/msg00738.html has the start of a patch.

[Steve Langasek (vorlon)]

patch done and tested, now finalizing the package for upload.

[Launchpad Janitor (janitor)]

This bug was fixed in the package eglibc - 2.10.1-0ubuntu6

---------------
eglibc (2.10.1-0ubuntu6) karmic; urgency=low

  * patches/all/submitted-missing-etc-hosts.diff: a missing /etc/hosts should
    be treated as a simple "not found", not as an internal error.
    LP: #408901.

 -- Steve Langasek <email address hidden> Tue, 11 Aug 2009 19:58:18 +0000

[Steve Langasek (vorlon)]

glibc 2.10 introduces a regression in getaddrinfo(); with a standard nsswitch.conf:

$ grep host /etc/nsswitch.conf
hosts: files dns
$

and no /etc/hosts file on the system (which is legitimate; e.g., in a chroot):

$ cat /etc/hosts
cat: /etc/hosts: No such file or directory
$

all calls to getaddrinfo() will fail, short-circuited by an nss_files failure
before invoking nss_dns.

Trivial test case, patch to follow.

[Steve Langasek (vorlon)]

Created attachment 4142
test case

[Steve Langasek (vorlon)]

Created attachment 4143
patch to nss_files fixing getaddrinfo when /etc/hosts is absent

[Drepper-fsp (drepper-fsp)]

I applied the patch.

[Hermier (hermier)]

Seems the fix is incorrect, on 2.11 I get:

bash-4.0# gcc bug-408901.c
bash-4.0# ./a.out www.redhat.com
www.redhat.com -5
bash-4.0# touch /etc/hosts
bash-4.0# ./a.out www.redhat.com
www.redhat.com 0

It seems that returning NO_DATA (in the patch) stops the host search
prematurely. Instead returning HOST_NOT_FOUND fix the issue, and sounds more
logical.

[Andreas Schwab (schwab-linux-m68k)]

Appears to be working fine with 2.17.