Setting the clock

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Dave J. Catling - 30 Jul 2003 22:32 GMT

Hi all.

I'm trying to set the system clock under OS X but can't see a way to do it.

Found the Carbon functions SetDateTime and friends and some others from the
man pages (settimeofday) although it appears that only root or superusers
can change the time.

What I'm aiming to do is use a handheld GPS device to synchronise the system
clock with UTC time so that a Mac Laptop can be used for recording data in
the field. I can manage this under OS9 with the Carbon routines just not
OSX (where it is wanted).

Any suggestions?

Thanks
Dave

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Matthew Russotto - 31 Jul 2003 16:30 GMT

>Hi all.
>
[quoted text clipped - 8 lines]
>the field. I can manage this under OS9 with the Carbon routines just not
>OSX (where it is wanted).

First, note that a handheld GPS is not usually a really good time source. I
don't think you can even guarantee being within a second with the NEMA
output.

That said, yes, you have to be root to set the time. So make yourself
root and do it.

You can also hook the GPS up as a 'reference clock' to ntpd, though I
haven't tried this with the OS X ntp setup.

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Matthew T. Russotto mrussotto@speakeasy.net
"Extremism in defense of liberty is no vice, and moderation in pursuit
of justice is no virtue." But extreme restriction of liberty in pursuit of
a modicum of security is a very expensive vice.

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Dave J. Catling - 31 Jul 2003 18:31 GMT

Inline:

> First, note that a handheld GPS is not usually a really good time source. I
> don't think you can even guarantee being within a second with the NEMA
> output.

Yeah, I know that, but it's being compared with other handheld GPS units so
hopefully between them all they should be moreorless in sync with each
other, and given the position accuracy I don't think a few tenths of a
second difference in time is going to affect things very much.

The current method is to try to set the time manually using a non-connected
time source (e.g. the talking clock)! NTP servers are out (no internet
service in the middle of a field).

I know there are probably far better methods available that give greater
accuracy but these all cost money.

> That said, yes, you have to be root to set the time. So make yourself
> root and do it.

Yup, got that far today - continually learning about the Mac OS, just when I
thought I had OS9 understood ... Should be possibly to write an app that
runs from the terminal once logged in as root to set the system clock.

> You can also hook the GPS up as a 'reference clock' to ntpd, though I
> haven't tried this with the OS X ntp setup.

As I understand it the clock won't correct itself instantly but instead
'drifts' to the correct time. For this application I need to set the time
that is shown on the GPS.

I just need to sort out the problems with serial communication now and I'm
sorted!

Thanks for the reply
Dave

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Mac Forum / Programming / CodeWarrior / July 2003

Setting the clock