[ntp:questions] ntpd deletes IPv6 interface after startup

Hauke Lampe packbart at blagga.openchaos.org
Sun Nov 11 17:44:39 UTC 2007


Frank Kardel schrieb:

> Have you checked via ifconfig -a that the interface are still listed
> when ifiter fails to enumerate them  ?

Yes, the interface state has not changed since the last reboot. It's up and 
reachable from the outside.

> Please file a bug at http://bugs.ntp.org. Be sure to include detailed
> information about your operating system.

I did a bit more research for a bug report.

Due to a bug in my debugging output (d'Oh!), ntpd appeared to use 
getifaddrs while in fact it used ifiter_ioctl. As I understand it, glibc's 
getifaddrs() supports only IPv4 and libinet6 is not available on my system.

By alternating configuration options, I found that the problem manifests 
only when ntpd chroots itself. I usually start ntpd with

-u ntpd:ntpd -i /var/lib/ntp

to chroot and drop root privileges after startup. Without the -i option, 
ntpd binds to all interfaces and keeps listening, whether or not it changes 
UID to user ntpd.

After chroot, /proc/net/if_inet6 isn't available to ifiter_ioctl anymore.

So, I don't think it's a real bug, although an unexpected nuisance.

The options AFAIK see, are:

- change ifiter_ioctl to enumerate IPv6 interfaces through a socket call as 
  it does for IPv4. I don't know if that's even possible.
- install libinet6 to enable getifaddrs(). This looks possible, but I'm not 
  sure I really want to go there
- don't use chroot
- mount proc on /var/lib/ntp/proc
- keep running with -U 0

I'll stick with -U 0 for now as it doesn't seem to do any harm, even after 
I shut an interface down and brought it up again.

Should I still file this as a bug?

I added a note to
http://support.ntp.org/bin/view/Support/KnownOsIssues#Section_9.2.3.2.5.1.



Hauke.




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