Re: AW: AW: [chrony-users] chrony: Use of RTC trimming together with ntpdate: A Bad Thing ?

[Ed W <lists@xxxxxxxxxxxxxx>]

On 31/08/2011 08:11, thomas.schmid@xxxxxxxxx wrote:
>
> Again the problem is to find out *when* I can remove the temporary default route which
> facilitates the access to the NTP servers when using chronyd's "initstepslew".
>

I think you have most of the answers already in this thread.  Just to
add a couple of extra ideas

- Chrony can be "offline" and then "online" on demand. Idea: boot up
with the wrong time and specifically bring chrony online/update/offline
in a careful coordination with some script controlling connectivity

- Gentoo's OpenRC has an init.d file called swclock. This touches some
file on the disk at shutdown and then at bootup sets the clock to the
time on the file. This doesn't give you accurate time "now", but it does
at least ensure that time is monotonically increasing.  Idea: Some
variation of this to detect battery failure or other massive clock skew
on boot. Possibly even use it to set a "working" time while you wait for
some external source to become available

- Routing can be controlled based on "source" (and obviously on
destination). Not going to give you a full explanation here, but you can
get quite fancy with routing and set it to route somewhere based on the
process owner (chrony), the destination/source ports/ip, time of day,
forced through only certain network devices, etc.  Idea: have a play
with Shorewall and it's tcrules + the multi-ISP stuff until you
understand the intricacies. Based on that you can ditch shorewall and
build your own script which achieves what you need (Shorewall is just a
neat tool which helps you get a foot up on what is quite advanced
stuff).  It's quite possible that the routing can be set and left rather
than needing some complex dance (although based on other answers in the
list it should be possible to "wait" on chrony doing it's initstep stuff)


I'm building something completely different, but I have similar
requirements to try and get accurate time at boot for an unattended
router type device.  I'm also considering including a BlueNext GPS that
appears to come in around the $16 mark (if someone knows of a cheaper
source for USB GPS units then interested to hear?)

Good luck

Ed W

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