Cannot set config file in /etc/default/ntp

[Alexander Garden]

Description: Ubuntu 12.04 LTS
Release: 12.04

ntp:
  Installed: 1:4.2.6.p3+dfsg-1ubuntu3.1
  Candidate: 1:4.2.6.p3+dfsg-1ubuntu3.1
  Version table:
 *** 1:4.2.6.p3+dfsg-1ubuntu3.1 0
        500 http://us.archive.ubuntu.com/ubuntu/ precise-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     1:4.2.6.p3+dfsg-1ubuntu3 0
        500 http://us.archive.ubuntu.com/ubuntu/ precise/main amd64 Packages
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I had a need to set a custom config file for ntp. I looked about and found that I could pass a '-c' option and that options for ntp are set in /etc/default/ntp in NTPD_OPTS. So I put it in there: NTPD_OPTS='-g -c /path/to/custom/ntp.conf'. It worked. Until I deployed to another box that was receiving NTP settings via DHCP. On that box, ntpd exited with an error because it had received two config files in its arguments. Not good.

After reading through the init script, I opted to add a new variable to /etc/default/ntp specifically for holding a custom config file. Attached is a patch that will use that value if DHCP has not created its own ntp.conf. If NTP settings were passed via DCHP, then those settings will override the custom config file.

[Ubuntu Foundations Team Bug Bot (crichton)]

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[Christian Ehrhardt  (paelzer)]

I know it's a long time, but I'm cleaning up old NTP bugs atm.

The patch looks good, this will need another patch with an example to the config file.
Setting triaged since one can start working on it.

Although I'm not sure if this is worth a delta, so if one is starting to work on it maybe we should fix it in Debian right away and pick it up in the next sync.

[Robie Basak (racb)]

Thank you Alexander for submitting this patch, and to Christian for catching up on old bugs. I'm reviewing Christian's merge proposal at https://code.launchpad.net/~paelzer/ubuntu/+source/ntp/+git/ntp/+merge/299122 which includes this patch but thought it would be more inclusive to discuss it directly in this bug.

There is a risk in introducing a new configuration variable in a delta in Ubuntu. If Debian don't adopt exactly the same thing, it means that we have to maintain a delta indefinitely in Ubuntu, since to then sync with Debian would mean breaking users on upgrade. In this case, Alexander will set the new NTPD_CONF variable and after a sync, Alexander will upgrade to a version where this silently stops working. Christian said "I'm not sure if this is worth a delta" and for this reason I agree.

Instead, I propose that it doesn't make sense for the system to be configured to request NTP configuration via DHCP and then not use it. So I think a more appropriate solution is to expect users who want to override ntp.conf to also disable NTP-by-DHCP in dhclient's configuration. Then /var/lib/ntp/ntp.conf.dhcp would not exist and this problem wouldn't arise. dhclient packaging should also ensure that the file is deleted when it is no longer relevant. If this is not currently possible, I think a fix should be in dhclient's package to make this easier, rather than in ntp to ignore the supplied configuration.

Alexander said "On that box, ntpd exited with an error because it had received two config files in its arguments. Not good." and I agree. Note though that with Alexander's patch, this can still happen - the patch just provides a workaround at configuration level. My proposal doesn't solve this problem either, I admit; my alternative workaround is to adjust dhclient.

So I'm proposing a "Won't Fix" for ntp in Ubuntu, and to add a task for dhclient if necessary. We can of course take whatever Debian want to do, since then we don't incur a maintenance burden. If Debian wants to add $NTPD_CONF, I have no objection. So thank you Christian for filing this in Debian. But I don't think we should add it in a delta in Ubuntu because of the pain of the divergence from Debian in this case.

[Christian Ehrhardt  (paelzer)]

@Robie
thank you for the great explanation.
I agree with you that with these extra details my "I'm not sure" should become a "lets not add delta" for this.

I also like the suggested workaround - FYI here is a good summary of how to actually do that:
=> http://serverfault.com/questions/329596/how-to-override-the-ntp-information-sent-by-dhcp-in-debian

Fortunately with the git commits this can easily be removed from the merge.
Please let men know if you want me to change and push something.

But - waiting for user feedback if we overlook something first.

[Alexander Garden (tolaythisbodydown)]

Thank you all for working on this.

Removing ntp-servers from the request in dhclient seems like a clean way of avoiding the collision. I am comfortable using that going forward and being able to put '-c mycustom.conf' in NTPD_OPTS.

[Robie Basak (racb)]

Thanks Alexander. Let's mark this Won't Fix for Ubuntu then.