[lug] laptop time

Timothy C. Klein teece at silverklein.net
Fri Feb 23 00:22:38 MST 2001

Ok, I am confused now by the terms.  Aren't the RTC and the CMOS clock
the same thing?   Or is the RTC the one in the kernel? 

Either way, if you set the clock on your system board (BIOS, CMOS, RTC,
whatever we call it) to UTC (or GMT as it used to be called), Linux will
be happier about your machine's time.  By UTC I means Universal
Coordinated time, or the time in Greanwich (sp?), England (currently
-0700 from MST).  Your time will be goofed up, though, if you don't run
tzconfig and let the kernel know what offset to apply to UTC to get your
machine to display local time (Mountain Standard Time for me).
Thus, on my machine, I get:

Fri Feb 23 00:18:50 2001 MST  # This is my time in Denver

#rdate --utc
Fri Feb 23 07:18:59 2001 UTC  # This is the time to the linux kernel and BIOS

Hope *I'm* not totally confused ;)


On Thu, Feb 22, 2001 at 09:53:23AM -0500, Installer wrote:
> On Wed, 21 Feb 2001, Timothy C. Klein said:
> >Set your bios to GMT (or UTC, whatever you call it).  I suspect your
> >problem will go away.  If you run only linux, to do this adjust your
> >time to the correct time for MST, (rdate -s time.nist.gov is easy), then
> >do hwclock --systohc to sync the RTC in your laptop with that.
> >
> >I don't think you have to tell Linux that the RTC is in UTC (he he,
> >funny acronyms), but I could be wrong.  If that doesnt help, let me
> >know.  It is early in the morning and I am still sleepy.  You also need
> >to make sure that you run tzconfig and set your timezone correctly, so
> >that when linux asks for the time, it gets UTC first, and converts it to
> >local time for you.
> >
> >If you run Windows on the laptop, you may have to lie Linux about which
> >timezone you are (I would tell it you are in GMT), and make sure the
> >bios is set to local time.  But I don't like that approach.
> This has always been a little bit fuzzy for me.  Are you saying that you
> can set the CMOS clock to local time but have the Linux RTC run in
> GMT?  How would this affect timestamping in the filesystem?  I once tried
> setting the CMOS clock to RTC as recommended in one of the Howto's, but
> then it becomes a source of confusion when looking at fs timestamps, and
> also affects cron etc.  
> Here near the equator, the seasonal time changes for daylight savings is
> not an issue, because it doesn't exist.  This is given as a reason for
> using GMC in the kernel configuration help doc.
> If I could have the RTC transparently use GMT, I think that may be
> preferrable.
> ----------------------------------------------------------------------
> John Karns                                              jkarns at csd.net
> _______________________________________________
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== Timothy Klein       || And what rough beast                   ==
== teece at hypermall.net || Its hour come round at last            ==
== Aufwiedersehen!     || Slouches towards Bethlehem to be born? ==
== Aufwiedersehen!     || The beast of Redmond, nothing more.    ==

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