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Clock is slow problem - please help a newb!
http://forum.linhes.org/viewtopic.php?f=6&t=14206		 Page 1 of 1
Author:  edmicman [ Fri Feb 16, 2007 7:57 am ]
Post subject:  Clock is slow problem - please help a newb!
I've just realized that my MythTV clock seems to be slow - less than a minute, seems somewhere around 20-40 seconds or so. But enough that it misses the intro/beginnings of most shows that it's set to record. I'm not sure how long it's been going on, but the last few weeks it's been botching my Thursday night shows.

I'm running R5B7 on an Nforce4 board. When I ran "ntpdate" I got this:
Quote:
root@mythtv:~# ntpdate ntp0.cornell.edu
16 Feb 06:40:43 ntpdate[11632]: the NTP socket is in use, exiting
root@mythtv:~#


I also did this according to the wiki:
Quote:
1) su to root
2) nano /etc/lilo.conf
3) Find the "append" line
4) make the line as follows
append="apm=power-off nomce noapic noioapic"
5) Save changes
6) Run lilo
7) Reboot.


But it was still off. So pardon me being completely new to this, as I'm still learning my way around linux, but where do I go from here?

Is there a way to force a resync, or to tell how much the clock is off or something? I'm not that familiar with the clock commands in linux.

Is there another solution or something I should do? I'd change my programs to start a minute earlier, but I've got a PVR500 (2 tuners) and overlaps cause problems and make it not record programs because when one is a minute earlier another show is still recording.

Thanks for any help or advice!
Author:  bruce_s01 [ Fri Feb 16, 2007 8:10 am ]
Post subject: 
It can be difficult to tell if it's a problem with the clock, or a station being consistently off.
If you have access to teletext you should be able to compare it with the date command. If not, do you have anything like the speaking clock in your area just to check?

Bruce S.
Author:  edmicman [ Fri Feb 16, 2007 8:14 am ]
Post subject: 
Thanks, I'll check on that. Granted, that's part of the problem - I'm not sure if the local cable is off or what. But the cable box will switch to 8:30pm, and the show will start. If I pull up MythWeb at that moment, it still says 8:29 and is not recording. If I refresh a few times (within a short while), then the Myth box changes to 8:30 and begins recording. It's *close*, but it's missing some things.....sigh.....
Author:  slowtolearn [ Fri Feb 16, 2007 8:30 am ]
Post subject: 
I had problems with ntpd on a couple of Slackware boxes, so I opted to use ntpdate each hour instead. You would need to do something along the lines of:
Code:
/etc/init.d/ntp-server stop
update-rc.d -f ntp-server remove

Then add the following lines to /etc/cron.hourly/settime:
Code:
#!/bin/sh
/usr/sbin/ntpdate -v -b time-a.nist.gov

Then make /etc/cron.hourly/settime executable:
Code:
chmod 755 /etc/cron.hourly/settime


See if that helps your situation. If not, you can simply remove /etc/cron.hourly/settime and run
Code:
update-rc.d ntp-server defaults
to get back to where you were.
Author:  Martian [ Fri Feb 16, 2007 11:33 am ]
Post subject: 
Be careful with using ntp-date with a cron job. While it does work, if your clock has a fair amount of drift the sudden changing of the time can give some programs headaches. For example if your clock gains 8 seconds per hour. When that cron job runs it will jerk the clock back by 8 seconds. This "going back in time" could confuse some programs.

The ntp-server handles this much more graciously by slightly increasing or decreasing the clock to "catch-up" or "fall-back" to actual time gradually to avoid sudden leaps.

I would recommend only using the ntp-date / cron job solution as a last resort.

If you are experiencing substantial clock drift you may need to look at your BIOS settings for "spread spectrum" as this is known to cause clock drift issues in some cases. I had an nForce2 motherboard that suffered from this. A search for "clock drift spread spectrum" should get you started.

Good Luck,

Martian
Author:  slowtolearn [ Fri Feb 16, 2007 12:14 pm ]
Post subject: 
Martian wrote:
If you are experiencing substantial clock drift you may need to look at your BIOS settings for "spread spectrum" as this is known to cause clock drift issues in some cases. I had an nForce2 motherboard that suffered from this. A search for "clock drift spread spectrum" should get you started.
Very helpful Martian, thanks! I'll check into the BIOS settings on those systems that were causing headaches with ntpd.
Author:  bkamen [ Fri Feb 16, 2007 2:10 pm ]
Post subject: 
If you want, you can also set up ntpd to run all the time.

I like that the best then the computer can be a time server in the house as well (if you have more than one PC running)...
Author:  mjl [ Fri Feb 16, 2007 9:53 pm ]
Post subject: 
Hi,

In most of the installs / upgrades cesman has the ntpd start at the normal start up and if the clock is close should tweak it over a period time (hours ~ days?) to be really tight.

I put a one liner in my boot to do a one time tweak on boot / reboot before things get running and have had no issues. Using the original example:
# ntpdate ntp0.cornell.edu won't work, # ntpdate -u ntp0.cornell.edu should work.

# echo "ntpdate -u ntp0.cornell.edu" >> /etc/init.d/bootmisc.sh will add the inital clock set at boot so ntpd should be able to tweak the fine corrections gracefuly.

Mike
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