[ntp:questions] Automatic time synchronization of local hw clock.

Jochen Bern Jochen.Bern at LINworks.de
Thu Apr 17 13:22:55 UTC 2014


On 17.04.2014 14:00, questions-request at lists.ntp.org digested:
> From: Martin Burnicki <martin.burnicki at meinberg.de>
> 
> Usually it is sufficient to set the RTC on system shutdown, so that it 
> keeps time while the machine is powered off

That is, of course, assuming that the machine in question *has* an
*orderly* shutdown every now and then. Servers in well-protected
internal networks may well see far more crashes (and "WTH is the RTC set
to!?" questions by not-yet-initiated operators) than intentional shutdowns.

(Never tried it, but wouldn't laptops that get suspended and then
somehow are forced to go through a full reboot instead of a wakeup
circumvent that sync "schedule", too?)

> From: William Unruh <unruh at invalid.ca>
> 
> I do not believe that ntp ever considers it its job to write the rtc.

If I'm not *very* much mistaken, very old versions of (x)ntpd (predating
Linux' support of localtime RTCs to allow for a dual-boot setup with
Win, if not predating Linux altogether) contained code to do periodic
updates to x86 RTCs directly (assuming them to run on UTC, of course),
said functionality *missing* in the back-then Unixoid OSes on x86. Of
course, that went down in flames when non-UTC RTCs came a-knockin' and
required the OS to join in and do the UTC-localtime conversion for the
non-zone-aware players.

Regards,
								J. Bern
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