[PLUG] ntpd and subnet

[Larry Brigman]

If these laptops have CPU's that change frequency(or sleep) based on
load/temp, running ntpd is
problematic.  Also getting the machine into hibernate mode to be moved also
could cause problems.
Running ntpdate via cron is probably more than adequate.

ntpd can take up to two weeks to get time set < 1 second if things are far
off.
The default setting in ntp allows the service to make time jump to help
speed the
convergence of time.  This could be forward (not typically a problem) or
backwards (lots of problems).  Almost all programs consider time as a
constant and don't behave well when
that is not the case.

Also ntp expects the packet travel times to be symmetrical between the
client and server.
This probably isn't a problem for most systems if they only care for
accuracy around 10-100ms.




On Tue, Jun 24, 2014 at 10:49 AM, Rich Shepard <rshepard at appl-ecosys.com>
wrote:

>    The ethernet-connected hosts here have static IP addresses. The wireless
> access point serves dynamic IP addresses on a different subnet. Only two
> portables use the WAP and both have a time keeping issue: each machine
> gains
> time and can get days ahead.
>
>    While many of us wish we could gain time so everything can be
> accomplished, for the computers it is not desired. One laptop, a Toshiba
> Satellite running Slackware-14.1 booted and thought it was Thursday, June
> 26th, and 5:17 pm when it was only an hour ago. I reset the date and time,
> ran 'hwclock -w' to set the hardware clock to the system time, and shut
> down. Realizing that the reason users cannot run alsamixer was not having
> their usernames in the audio group, I rebooted. The system gagged because
> the last time /dev/sda1 was checked was Thursday the 26th and now it is
> Tuesday the 24th and it doesn't know how to deal with back to the past.
> That
> was fixed by running 'e2fsck -v -y' and waiting.
>
>    So, now the kernel is happy, and I need to figure out why only the two
> portables that connect to the 'Net wirelessly through the WAP keep gaining
> time. I've set up one of the laptops to use na.pool ntp servers but it
> still
> keeps gaining time. My Web searches and thread on linuxquestions.org have
> produced no solution for the one laptop; just this morning I saw the second
> has the same problem and realized the common factor is wireless
> connectivity.
>
>    Any ideas of why only the portables connecting via the WAP keep gaining
> time would be much appreciated. Also, any diagnostics or tests I can run to
> isolate the source of the problem would be good.
>
> TIA,
>
> Rich
>
> _______________________________________________
> PLUG mailing list
> PLUG at lists.pdxlinux.org
> http://lists.pdxlinux.org/mailman/listinfo/plug
>