[PLUG] Linux Time?

[King Beowulf]

On 10/22/2017 12:49 PM, Dave Lien - W7DAL wrote:
> /... //the install process usually sets it up for you./
> 
> Thanks Jim and Larry!
> 
> I've been watching the flow of contacts using FT8 over the past several 
> days without doing anything about time correction. With continuously 
> positive results over many hours of system ON time I now have no reason 
> to believe drift is a factor to be addressed.
> 
> Also, I've never seen a reference to having to add special time adjust 
> software when Linux is used with this time critical digital 
> communications mode. Such a software addition is pretty much mandatory 
> with Windows and is well publicized by FT8 and other digital mode users.
> 
> So, I've decided to just leave things alone. . TNX.


Just as an FYI (and late to the party as usual), I have this is my start
up /etc/rc.d/rc.local, along with the appropriate settings in :

# Set the time
/usr/sbin/ntpd -qg
/sbin/hwclock -w

This syncs up both hardware and system clocks at the end of the boot cycle.

The motherboard hardware clock can and does drift a bit over long time
scales. These clock chips have always been awful.  It does not matter
the OS you are running.  The system (software) clock is even worse,
although does not seem to be as bad as in Windows.

http://www.tldp.org/HOWTO/Clock-2.html

Running ntp continuously is a bit overkill for my needs.  Here is my
time drift on recent reboots for kernel and nvidia driver updates:

# last reboot
reboot   system boot  4.4.88           Fri Oct 13 00:58 - 13:10 (9+12:11)
reboot   system boot  4.4.88           Thu Oct 12 15:07 - 00:57  (09:50)
reboot   system boot  4.4.75           Mon Sep  4 13:32 - 15:05 (38+01:32)

# cat messages.2 |grep ntpd
Oct 12 15:07:20 gandalf ntpd[1431]: ntpd 4.2.8p10 at 1.3728-o Thu Apr 20
17:49:20 UTC 2017 (1): Starting
Oct 12 15:07:20 gandalf ntpd[1431]: Command line: /usr/sbin/ntpd -qg
Oct 12 15:07:20 gandalf ntpd[1431]: proto: precision = 0.114 usec (-23)
...
Oct 12 15:07:29 gandalf ntpd[1431]: ntpd: time set +2.169528 s
Oct 13 00:59:03 gandalf ntpd[1432]: ntpd 4.2.8p10 at 1.3728-o Thu Apr 20
17:49:20 UTC 2017 (1): Starting
Oct 13 00:59:03 gandalf ntpd[1432]: Command line: /usr/sbin/ntpd -qg
Oct 13 00:59:03 gandalf ntpd[1432]: proto: precision = 0.111 usec (-23)
...
Oct 13 00:59:12 gandalf ntpd[1432]: ntpd: time slew +0.032806 s

Thus, after an uptime of 38 days, the time drift was +2.169528 s and
then after 9 days, +0.032806 s.  For comparison, after 20 days up, my
antique ~10 yrs old HP Pentium 4 box (Intel motherboard) drifted
+81.659436 s

It all depends on your application and needs as to how accurate you
computer time needs to be. For time critical software, depending on the
actual motherboard drift, you can calculate any required ntp update
interval.

-Ed