Re: [chrony-users] Notification from Chrony about change in time

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On Mon, Oct 03, 2016 at 09:30:49AM +0000, Jahagirdar, Bhushan wrote:
> Hi,
> Is there any way to know if Chrony has updated the system time? I mean an interface, event or a possibility of a callback from Chrony.

Are you interested in all adjustments of the clock or only some of
them like steps or slews largers than some threshold?

The only possibility of a real callback is the mailonchange directive,
which sends email when an adjustement reached a threshold. You could
use the --with-sendmail option to compile chronyd with a different
path to the sendmail binary in order to execute any binary or script
you need.

There might be other possibilities depending on what adjustments you
need to detect:
- monitor the tracking log for new entries
- periodically check the chronyc tracking output
- periodically check the reference timestamp of chronyd operating as
  an NTP server

If you need to detect steps only, on Linux you could write a small C
program which creates a timer with infinite timeout and the
TFD_TIMER_CANCEL_ON_SET flag, which will expire when the clock is
stepped by any daemon.

Miroslav Lichvar

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