[arch-general] Systemd and time synchronisation problems

Stephen E. Baker baker.stephen.e at gmail.com
Wed Sep 12 08:02:26 EDT 2012

On 11/09/2012 5:22 PM, mike cloaked wrote:
> On Tue, Sep 11, 2012 at 8:06 PM, mike cloaked <mike.cloaked at gmail.com> wrote:
>> On Tue, Sep 11, 2012 at 7:51 PM, Jan Steffens <jan.steffens at gmail.com> wrote:
>>> On Tue, Sep 11, 2012 at 8:27 PM, Thomas Bächler <thomas at archlinux.org> wrote:
>>>> 2) When chrony is not running, systemd-timedated runs periodically to
>>>> adjust the hardware clock for drift (AFAIK, not sure that is the job
>>>> that timedated does).
>>> No. When chrony isn't running, the hwclock isn't getting adjusted at
>>> all. The only thing systemd does on startup is warp the system clock
>>> if and only if the RTC is running in localtime.
>>> systemd-timedated's job is to provide a DBus interface to change
>>> system time and date settings:
>>>    SetTime, SetTimezone, SetLocalRTC (whether RTC is in localtime),
>>> SetNTP (whether NTP is enabled)
>>> It's used by gnome-control-center, at least. The SetNTP call uses the
>>> ntp-units.d directory to select an implementation.
>> Thank you for all the information - it seems that the key to this was
>> that the RTC was too far out from correct time at boot - now that I
>> manually set the RTC to correct time it comes up close to correct -
>> and then chrony synchronises a few minutes after startup.  At present
>> tracking shows it is about 0.1 microsecs from NTP time:
>> System time     : 0.000000106 seconds fast of NTP time
>> What  I don't understand is why the hardware clock was not re-written
>> with the correctly synchronised time previously, since chrony has been
>> running every time I booted the system for ages?
> By the way I also found another way to write the hardware clock from
> within chrony which does not need the chronyd daemon to be stopped
> (after spending this evening reading the detailed chrony docs!)  that
> you can run chronyc in a terminal, and then enter "password
> mypasswordforchrony"  (where the argument is the password from the
> chrony keys file) and then issue the "trimrtc" command once the chrony
> password has been accepted - this will then write the current system
> time to the RTC, only sensible if time has been synchronised - though
> the RTC is only accurate to within a second or so I believe.
> I guess it would be nice to have more complete information on the
> archwiki though there is full documentation on the chrony main web
> page.
I think the usual response is, anyone can edit the wiki - please add 
what you
think is needed.

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