[chrony-users] Minimal online duration

[Ariel Garcia]

Hello,

my use case for chrony is on a device which is connecting for a few seconds
every 12 hours to send data. An initial synchronization time on first boot will
of course take longer, that's ok.
The ppp deamon will set chrony servers online / offline when the link is on/off.

Assuming the servers are reachable/fine, would a short connection time of
2-3 seconds twice per day be enough to keep synchronized, or should i rather
enforce some minimum "on" time? (no big precision required, just within 1s)

Can anybody with a similar use-case comment on experience?

My relevant config is:
-----------
server SERVER1/2/3 auto_offline offline iburst presend 10 minpoll 4
initstepslew 3600 SERVER1/2/3
makestep 3600 2
fallbackdrift 13 19
driftfile /var/lib/chrony/sysclock.drift
dumpdir /var/lib/chrony/history
dumponexit
-----------

Thanks in advance!
Ariel

[Miroslav Lichvar]

Post by Ariel Garcia
Assuming the servers are reachable/fine, would a short connection time of
2-3 seconds twice per day be enough to keep synchronized, or should i rather
enforce some minimum "on" time? (no big precision required, just within 1s)

That should be ok. 1 second per 12 hours is a frequency error of 23
ppm. Unless the clock on the board is very unstable, its error should
stay well below that.

Post by Ariel Garcia
server SERVER1/2/3 auto_offline offline iburst presend 10 minpoll 4
initstepslew 3600 SERVER1/2/3

If you don't need chronyd to block the boot sequence until the clock
is stepped I'd suggest to drop the initstepslew directive

Post by Ariel Garcia
makestep 3600 2
fallbackdrift 13 19
driftfile /var/lib/chrony/sysclock.drift
dumpdir /var/lib/chrony/history
dumponexit

That looks ok.

[Ariel Garcia]

Post by Miroslav Lichvar

Post by Ariel Garcia
Assuming the servers are reachable/fine, would a short connection time of
2-3 seconds twice per day be enough to keep synchronized, or should i
rather enforce some minimum "on" time? (no big precision required, just
within 1s)

That should be ok. 1 second per 12 hours is a frequency error of 23
ppm. Unless the clock on the board is very unstable, its error should
stay well below that.

i'm not (so) worried by the precision, but rather if chrony manages to
"exploit" in a useful way the single query to each server that it will manage
to send in those 2-3 seconds window.
There seems to be an implicit "yes" in you answer :)

Post by Miroslav Lichvar

Post by Ariel Garcia
server SERVER1/2/3 auto_offline offline iburst presend 10 minpoll 4
initstepslew 3600 SERVER1/2/3

If you don't need chronyd to block the boot sequence until the clock
is stepped I'd suggest to drop the initstepslew directive

ok thanks for the hint!

BR, Ariel

[Bill Unruh]

William G. Unruh __| Canadian Institute for|____ Tel: [phone]
Physics&Astronomy _|___ Advanced Research _|____ Fax: [phone]
UBC, Vancouver,BC _|_ Program in Cosmology |____ ***@physics.ubc.ca
Canada V6T 1Z1 ____|____ and Gravity ______|_ www.theory.physics.ubc.ca/

Post by Ariel Garcia

Post by Miroslav Lichvar

Post by Ariel Garcia
Assuming the servers are reachable/fine, would a short connection time of
2-3 seconds twice per day be enough to keep synchronized, or should i
rather enforce some minimum "on" time? (no big precision required, just
within 1s)

That should be ok. 1 second per 12 hours is a frequency error of 23
ppm. Unless the clock on the board is very unstable, its error should
stay well below that.

i'm not (so) worried by the precision, but rather if chrony manages to
"exploit" in a useful way the single query to each server that it will manage
to send in those 2-3 seconds window.
There seems to be an implicit "yes" in you answer :)

Sure it would use it. You should however tell chrony to do a burst when the it
comes online.

Post by Ariel Garcia

Post by Miroslav Lichvar

Post by Ariel Garcia
server SERVER1/2/3 auto_offline offline iburst presend 10 minpoll 4
initstepslew 3600 SERVER1/2/3

If you don't need chronyd to block the boot sequence until the clock
is stepped I'd suggest to drop the initstepslew directive

ok thanks for the hint!
BR, Ariel
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