Re: PROBLEM: Linux updates RTC secretly when clock synchronizes

[Pavel Machek]

Hi!

> PROBLEM: Linux updates RTC secretly when clock synchronizes.
> 
> Please CC replies etc to Ian Maclaine-cross <[e-mail]>.
> 
> When /usr/sbin/ntpd synchronizes the Linux kernel (or system) clock
> using the Network Time Protocol the kernel time is accurate to a few
> milliseconds. Linux then sets the Real Time (or Hardware or CMOS)
> Clock to this time at approximately 11 minute intervals. Typical RTCs
> drift less than 10 s/day so rebooting causes only millisecond errors.
> 
> Linux currently does not record the 11 minute updates to a log file.
> Clock programs (like hwclock) cannot correct RTC drift at boot without
> knowing when the RTC was last set. If NTP service is available after a
> long shutdown, ntpd may step the time.  Worse after a longer shutdown
> ntpd may drop out or even synchronize to the wrong time zone.  The
> workarounds are clumsy.
> 
> Please find following my small patch for linux/arch/i386/kernel/time.c
> which adds a KERN_NOTICE of each 11 minute update to the RTC. This is
> just for i386 machines at present. A script can search the logs for
> the last set time of the RTC and update /etc/adjtime.  Hwclock can
> then correct the RTC for drift and set the kernel clock.

That seems as very wrong solution.

What about just making kernel only _read_ system clock, and never set it? 
That looks way cleaner to me.

								Pavel
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