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Old 27th March 2012, 11:00 AM
old486whizz Offline
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Posts: 33
windows_xp_2003firefox
hwclock rewinding time on boot? (F15)

Heya guys,

I haven't come across this before, and a search in the forum only turns up this result: http://forums.fedoraforum.org/showthread.php?t=39906 .
I've also searched google but can only find man pages and information about setting my timezone (which is set).

SO, let's describe the problem:
I had to boot my laptop today, booted up and noticed the time had gone back by 1 hour on my desktop taskbar.
I assumed it was some NTP problem and ignored it.
After another stop/start of my server, I noticed the time had gone back yet another hour - and so was 2 hours out of sync.

So I started investigating by setting my BIOS time to the local time (UTC+1, which is BST).
I then booted into single-user mode, to make sure there was no network or strange service interference.

So, if UTC is 09:32::

In dmesg I see this:
Code:
[ 0.431101] Time: 10:32:13  Date: 27/03/2012
So the kernel is picking up the time from the BIOS just fine...

After the terminal comes up, then I get:
# date
Tue Mar 27 09:33:56 BST 2012
# date -u
Tue Mar 27 08:33:57 UTC 2012

... Why does it think UTC is 1 hour behind?

I looked at systemctl, and found that hwclock is being called with the "--systz" parameter, which acts slightly different to the "--hctosys" one (eg, doesn't go off to the hardware all the time).

# hwclock -r
Tue Mar 27 10:34:24 BST 2012
# hwclock -u
Tue Mar 27 11:34:33 UTC 2012

Now I understand this! The BIOS is in local time (UTC+1), so hwclock -r would be 'right'.
But even if I set my local clock to be UTC (09:30) the time will just continue to go backwards!!

So, time for the final test to show it is indeed hwclock --systz doing this:

# hwclock --systz
# date -u
Tue Mar 27 09:34:24 UTC 2012
# hwclock --systz
# date -u
Tue Mar 27 08:34:24 UTC 2012

So, I check my timezone data:
# md5sum /etc/local* /usr/share/zoneinfo/GB*
All output's return the SAME checksum - so the files are identical.

So, it seems like hwclock is doing something strange with the timezone, thinking the time it's getting is local-time, then trying to set the date with the UTC time (but without specifying it's UTC time).

After running a quick strace on the command I've seen it touches /etc/adjtime (I haven't any knowledge on that file yet) so I will start investigating that.

... But, "hwclock -s" set's the time correctly - directly from the BIOS.

... Can anyone offer words of wisdom?
There isn't a BIOS option for UTC that I can see.
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  #2  
Old 27th March 2012, 03:55 PM
Gareth Jones Offline
Official Gnome 3 Sales Rep. (and Adminstrator)
 
Join Date: Jul 2011
Location: Birmingham, UK
Age: 31
Posts: 2,771
linuxfirefox
Re: hwclock rewinding time on boot? (F15)

Run system-config-date and check that everything is reasonable. Also see this thread: http://forums.fedoraforum.org/showthread.php?t=277957, which sounds like it might be a similar problem.

Last edited by Gareth Jones; 27th March 2012 at 03:55 PM. Reason: Fixed wrong command...
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  #3  
Old 12th April 2012, 01:32 PM
old486whizz Offline
Registered User
 
Join Date: Jan 2008
Posts: 33
linuxfirefox
Re: hwclock rewinding time on boot? (F15)

Thanks for the reply.
I found a bugzilla bug against this and after reading through it thought it would be far more easier if I just set the BIOS to UTC (since that then fixed the issue at hand).

The bugzilla said it was not a fault (which has got to be incorrect, since the binary clearly keeps moving the time back by an hour) - but it did point me to a useful link.

So now, /etc/adjtime contains "UTC", the BIOS is in UTC time, and all is well with the world.

I just had to go into Windows and set it to store the time in UTC in the BIOS and viola!
... I feel dirty every time I boot into Windows on it.
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