[ntp:questions] Red Hat vote for chrony

William Unruh unruh at invalid.ca
Sat Dec 6 21:57:38 UTC 2014

On 2014-12-06, Paul <tik-tok at bodosom.net> wrote:
> On Sat, Dec 6, 2014 at 11:12 AM, William Unruh <unruh at invalid.ca> wrote:
>> And in my tests 10 years ago or so, I used a local gps clock to test the
>> ability of chrony and ntpd to discipline a computer clock networked to
>> another server which was disciplined by a gps. Thus the network was the
>> same, and the difference was ntpd vs chrony.
>> chrony was better. Primarily, I think, because chrony responded more
>> quickly to drift rate changes due to temp changes.
> I looked at your data back in the day.  Even then I thought they were old.
> Of course if the secret sauce is loop constants (I haven't read the Chrony
> architecture document, maybe because there isn't one) then perhaps the
> results would still be the same.

They are old, and naive. A much better job could be done. However, they
are indicative. As I mentioned it would be a really good project to have
someone do a better comparison-- both simulated for example with
Lichvar's simulation software, and real life measurements.

> Using chrony over ntp has also other advantages:
>    - smaller memory footprint (1.3MB vs 6MB resident size)
>    - no unnecessary process wakeups, this is good for powersaving. The ntpd
>    process normally wakes up every second.

That is to impliment the in-house frequency scaling on systems where
userland has no way of changing the frequency of the system clock. Under
linux and adjtimex one can alter the system clock (by up to 10% of
nominal,-- ntpd only uses max 500PPM, while chrony can use the full
I do not know if ntpd shuts off that "once per sec" if the system clock
can be altered in the kernel. 

>    ...
> For me it's consistency.  I want to run the same timekeeping software
> "everywhere"* and Chrony doesn't run "everywhere".

True and fair enough. Chrony only works on Linux or bsd systems. (That could probably be
expanded to include OsX but I do not know if it does out of the box). It
does not do Windows, so if you have windows machines, chrony is not an
option. But then this thread was about Redhat, which is Linux.

> *my everywhere is obviously not anyone else's everywhere.

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