[ntp:questions] ntpdate works, but ntpd doesn't (reach = 0)

Danny Mayer mayer at ntp.org
Fri Feb 13 04:11:57 UTC 2009

Martin Burnicki wrote:
> Danny Mayer wrote:
>> Uwe Klein wrote:
>>> Richard B. Gilbert wrote:
>>>> Uwe Klein wrote:
>>>>> See:
>>>>> currently on SuSE systems 'rcntpd restart' is run on any interface
>>>>> changes.
>>>> Looks like a SuSE problem rather than an ntpd problem!
>>> Not really distribution specific. Look into the ip_up/down stuff
>>> on any linux system.
>>> Its a dynamic IP problem and its a ntpd problem due to no
>>> signaling path for interface changes.
>>> ( there have been some improvements very recently? )
>>> uwe
>> ntp 4.2.4 supports dynamic interfaces even if it cannot detect the
>> change directly. The O/S does not need to worry about this for ntpd.
> This is only supported kind of reasonably since 4.2.4p5. In earlier versions
> it may have taken very long time after an interface has appeared until ntpd
> re-tried to use it and mobilize associations.

It really makes no difference, especially once ntpd is stable. The
default is every 5 minutes and you can change that with the -u
command-line option.

> So there's no wonder why the Linux distributors tried to implement some
> workarounds (e.g. control ntpd from ifup/ifdown) to speed things up.

That's because they didn't realize that it's no longer necessary.

> There are *not* only servers running 24/7 which use NTP.

I know that. My laptop never shuts down. It changes IP addresses all the
time as I move from office to conference room and back again and then home.

> Martin

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