Re: [PLUG] Linux Time?

[Dave Lien - W7DAL]

Thank You Ed!


On 10/22/2017 1:47 PM, King Beowulf wrote:
> 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@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@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
>
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Re: [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@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@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

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Re: [PLUG] Linux Time?

[Dave Lien - W7DAL]

/... //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.
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Re: [PLUG] Linux Time?

[Jim Garrison]

On 10/21/2017 5:12 PM, Dave Lien - W7DAL wrote:
> TNX Larry. I discovered that NTP is already present as part of the Mint 
> 18.2 default installation. Can I assume from this that is probably 
> active? Is there a simple command to determine it's status? -Dave.

Both ntpq and ntpdc will display the current status.  The 'pe' command
displays the status of the peers.

[jhg@janus ~]$ ntpq
ntpq> hostnames no
ntpq> pe
 remote   refid  st t when poll reach   delay   offset
jitter
==
*152.2.133.53.PPS.1 u  549 1024  377   95.099   -3.895
2.996
+129.6.15.28 .NIST.   1 u  722 1024  377   96.8112.228
5.503
-72.5.72.15  162.213.2.2532 u  402 1024  377   30.7095.615
1.761
+52.6.160.3  209.51.161.238   2 u  583 1024  377   90.1341.960
1.645


This tells me that I'm synced (*) to 152.2.133.53, which is a
top-level "Stratum 1" time server, probably getting its time from GPS
or another atomic clock standard.  It's just a hair over 95ms away and
currently my clock is 3.895ms behind it.  Other candidates (+) are
129.6.15.28 and 52.6.160.3, while the outlier is 72.5.72.15, which
will not be used.

Synchronizing time is quite a complex and arcane topic, see
http://doc.ntp.org/ for more detail than you'll ever need to know.
When there is an offset, the local ntp daemon does not step the clock,
to prevent problems with software that might have a problem with
discontinuities (especially backwards discontinuities). Instead it
slightly adjusts the clock frequency to bring it slowly into sync.
The ntpdate utility is usually run once at bootup and DOES reset the
clock in one step if necessary, but ongoing sync is accomplished by
modulating the local clock frequency.

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Re: [PLUG] Linux Time?

[Dave Lien - W7DAL]

TNX Larry. I discovered that NTP is already present as part of the Mint 
18.2 default installation. Can I assume from this that is probably 
active? Is there a simple command to determine it's status? -Dave.


On 10/21/2017 3:11 PM, Larry Brigman wrote:
> Linux time correction software is ntp or chrony.  Ntpdate can be run
> instead if the machine is not on all the time.
>
>
> On Oct 21, 2017 1:12 PM, "Dave Lien - W7DAL"  wrote:
>
>> I've just begun running FT8 on Linux Mint (works great!) but am
>> wondering if I need to add time correction software like DIM4 as used
>> with Windows? Or does modern Linux auto-adjust the time to high
>> precision each time it is booted? Thanks! Dave.
>>
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Re: [PLUG] Linux Time?

[Larry Brigman]

Linux time correction software is ntp or chrony.  Ntpdate can be run
instead if the machine is not on all the time.


On Oct 21, 2017 1:12 PM, "Dave Lien - W7DAL"  wrote:

> I've just begun running FT8 on Linux Mint (works great!) but am
> wondering if I need to add time correction software like DIM4 as used
> with Windows? Or does modern Linux auto-adjust the time to high
> precision each time it is booted? Thanks! Dave.
>
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Re: [PLUG] Linux Time?

[Jim Garrison]

On 10/21/2017 1:04 PM, Dave Lien - W7DAL wrote:
> I've just begun running FT8 on Linux Mint (works great!) but am 
> wondering if I need to add time correction software like DIM4 as used 
> with Windows? Or does modern Linux auto-adjust the time to high 
> precision each time it is booted? Thanks! Dave.

Linux has used the NTP Daemon ntpd(8) for time sync for many, many
years.  It's part of all distributions AFAIK, and the install
process usually sets it up for you.

See https://en.wikipedia.org/wiki/Ntpd as a starting point.

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