[ntp:questions] Which version of Linux works best?

unruh unruh at wormhole.physics.ubc.ca
Wed Mar 10 20:38:13 UTC 2010

On 2010-03-10, David Lord <snews at lordynet.org> wrote:
> David J Taylor wrote:
>> Yes, I know it's one of those low long is a piece of string questions, 
>> but I'm now considering a dual-core Intel Atom system, which is 
>> "Compatible with Linux" according the the very minimal blurb I have 
>> right now.  If the system is to be used purely for NTP with Linux as a 
>> serial-port GPS/PPS stratum-1 server (and, yes, I know dual-core isn't 
>> needed for that, but I might want to boot Windows-7 64-bit 
>> occasionally), and considering that I know very little about Linux, 
>> which version of Linux would the group recommend?  Does it make any 
>> difference as far as timekeeping is concerned?

The key issues are whether or not the kernel is "power saving". You want
to switch that off-- the kernel slowing down and speeding up as the mood
takes it. You want to have it running at the same speed always ( what
that is does not matter, just that it is the same so the kernel
timekeeping does not get messed up.) Any kernel speed is far far higher
than needed for ntp-- and old 80486 would probably be sufficient- but
changes are a disaster. 

Since all distros use the same kernel ( with perhaps some mods) and ntp
package, there is really not much difference between distros. Some pile
on more junk than others. Use what you are familiar with. 

> "Linux" I think is just the kernel whilst filesystem and packages
> are very diverse between distributions.
> If you don't already know Linux well already then I'd suggest
> FreeBSD as being a more solid base than a Linux distribution.

I do not think there is any difference. 

> Otherwise I favour Slackware/Centos mainly because I'm more
> familiar with filesystem layout vs that of other distros such
> as Ubuntu.
> I have had chrony running on NetBSD but as with ntpd can't get
> most recent versions to install/run. It should be ok on Linux

ah. Could you please let the chrony people know what the problem is.
Bugs need to be and can be fixed. Have you tried the latest release
which came out about 1 month ago?

> and probably on FreeBSD but you'd need confirmation vs refclock
> drivers on FreeBSD for that.
> Certainly here on NetBSD chrony looks to give offsets a third or
> less than ntpd and avoids the square wave offset traces from ntpd
> that result from inability to correct for temperature changes,
> however I had problems with incompatibility between different
> chrony versions so given up to it until I have some spare system
> and time to work with.

?? chronyc must be the same version as chronyd. but what do you mean by

> David
>> Two secondary questions:
>> - how much better might FreeBSD be than Linux?  Any actual measurements?
>> - and one for Bill, how much better might chrony be than official NTP? 
>> Does it have a preferred Linux, or even freeBSD?

No prefered Linux. It does I believe run on BSD, but have never tried
it.  It has something like a factor of 3 better perfomance than ntpd,
primarily because it remembers the past ( ntpd forgets the past) and can
use that to imporve its estimates. It is also far far faster to converge
(minutes rather than half a day).

>> The system would /not/ be in a temperature controlled environment.

chrony corrects for temp variations far better than does ntpd. 
There are versions of ntpd which use on onboard thermometer to model and
compensate for temp variations, which have a much better performance
than straight ntpd does ( probably about the same level as chrony's
performance, which essentially uses the clock frequency as a temp

>> Thanks,
>> David

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