dmesg: Invalid time in clock: check and reset the date

[Ted Mittelstaedt]

> -----Original Message-----
> From: owner-freebsd-questions at freebsd.org
> [mailto:owner-freebsd-questions at freebsd.org]On Behalf Of Matthew Seaman
> Sent: Saturday, October 11, 2008 12:49 AM
> To: Richard Smith
> Cc: freebsd-questions at freebsd.org
> Subject: Re: dmesg: Invalid time in clock: check and reset the date
> 
> 
> Richard Smith wrote:
> > Hi, I've just installed FreeBSD 7.0 Release along with Windows 
> XP on my PC. I found that when I set the clock to the correct 
> time&date, next time I boot into FreeBSD it changes and reports 
> the wrong time&date. Both BIOS and Windows reports the time correctly.
> > 
> > dmesg shows the following message:
> > Invalid time in clock: check and reset the date!
> > 
> > Can't figure out what's wrong... any help will be appreciated.
> 
> Is the time out by an exact number of hours?[*]  Does the offset
> correspond to your localities' timezone offset from UTC?
> 
> If so, then what is happening is this: Windows will only deal with
> one timezone at a time, and it expects the system clock (and
> consequently the CMOS clock on the motherboard) to be set to the
> local wall-clock time.
> 
> Unix in comparison allows each process to be run in an arbitrary
> timezone, simply by setting the TZ environment variable.  It
> expects the system clock and the CMOS clock to be set to UTC, and
> it calculates the local offset as required.
> 
> When you reboot the machine, the internal system clock is set from
> the cmos clock, so one or the other OS will end up thinking local
> wall-clock time is UTC or vice-versa.  Unless you have the happy 
> fortune to be living in this Sceptered Isle (but only during the 
> wintertime), or in certain parts of West Africa that's going to
> cause problems.
> 
> If you need to dual-boot, FreeBSD provides a mechanism for allowing
> the CMOS clock to be set to wallclock time.  You can toggle the
> setting using /usr/sbin/tzsetup -- if there is a zero length file 
> /etc/wall_cmos_clock then your system is running in compatability
> mode.  Note: this file should not appear on a box that is dedicated
> to running FreeBSD[+] -- the tzsetup default is the /wrong/ choice
> in this case.
> 

No, it's not.

There is nothing wrong with running the CMOS clock on wall-clock
time even on a dedicated system.  You can do it any way you please.
Any real server should be synced by NTP in any case since the
internal RTC clock chip in a PC is not reliable or accurate.

Note that if you do run the CMOS clock on UTC that if your BIOS/CMOS
has a fancy auto-adjusting daylight savings time thingie in it, you
should disable that.

Ted