[ale] semi [OT] NTP questions - and NTP Windows - was: possibility of running an NTP server
Ron Frazier
atllinuxenthinfo at c3energy.com
Fri Jan 13 16:54:02 EST 2012
Hi guys,
As you know from prior threads, I've been doing lots of work with NTP
(as a client) recently. I've got my Linux machines running nicely, and
have turned my attention to Windows. I found a nice NTP port for
Windows that works great and has a really cool graphical interface and
graphical statistics monitor. It uses the same server configuration
lines as the Linux ntp.conf, although some parts of the configuration
file are different and customized to the Windows environment. See the
bottom of this message for links to screen shots of the NTP service
running under Windows. It's very cool.
The system is working, but has brought up even more questions.
Here you see a statistics image of how my system is performing using the
Windows NTP service. Note that the internal Windows NTP service is
disabled and replaced by this new program I installed.
http://dl.dropbox.com/u/9879631/ntp-mon15.jpg
NTP is polling the NIST service every 4 minutes, and, as you can see
from the red graph, my clock offset is all over the place, varying from
-5 ms to +110 ms. I also notice that the frequency is drifting up from
-13 to -9. Can someone explain to me in a few words what the frequency
means? Does this graph mean that the system is trimming my clock?
All this brings up more questions about how NTP works. I know that the
computer has a hardware and a software clock. I know the hardware clock
keeps the time when the system is off. When the OS boots, it gets time
from the hardware clock and then starts counting interrupts to maintain
the software clock, as I understand it. Based on my reading, it seems
that when the OS gets busy, it may disable the interrupts for fractions
of a second, which means it misses the clock interrupts. Therefore, the
system's software clock loses or gains time.
I want to know what NTP does with the hardware and software clocks. I
know it's polling NIST every 4 minutes, in this case, to get the correct
time. I know it sets the software clock and calculates and displays and
records the offset from true time each time. But, does the NTP daemon /
service also set the hardware clock at that time? If not, when does the
hardware clock get reset. Does it get set at shutdown?
While this method is working and keeping my clock within about 120 ms of
true time, it's polling NIST very frequently, although still within
their access policy. I'm thinking an alternative may be better. I've
noticed the polling interval almost never extends to longer settings, in
this case, whereas it does on Linux while still maintaining an offset of
under 20 ms or so.
I think that the hardware clock is probably much more accurate than the
software clock in Windows. I'd like to set the NTP system to poll the
hardware clock, say, every minute for 5-20 minutes. Then, at the end of
that time, I'd like it to poll an internet server like NIST and reset
both the hardware and software clocks. The net effect of this would be
something like the way the radio clocks work, synchronizing with NIST
once a night, and freewheeling in between those sync sessions. In this
case, continually synchronizing the software clock to the hardware
clock, assuming the hardware clock is any good, will keep the software
clock accurate while the system waits for an external sync. That way, I
think I could maintain reasonable accuracy while not having to ping NIST
every 4 minutes.
I'd also like to know if you can tell the NTP system that I can tolerate
a certain amount of error without it getting bent out of shape. For,
example, I might be willing to tolerate up to 400 ms of offset between
sync sessions.
Finally, I really like the way this Windows NTP program uses a GUI for
configuration and statistics. I'd like to know if there is anything
similar on my Linux systems.
I don't think they've changed this NTP program in a couple of years, but
it does it's job. If you'd like to get this Windows NTP program for
your own use, you can get it at the links below:
- Read the documentation here:
http://www.meinberg.de/english/sw/readme-ntpinstaller.htm
- Download the Windows NTP service / daemon package here (install this
first):
http://www.meinberg.de/english/sw/ntp.htm
- Download the GUI and statistics system here (install this second)
http://www.meinberg.de/english/sw/time-server-monitor.htm
Install the daemon / service and get it going. Let it set up the
default config file and, say, pick some US pool servers. Then, install
the time server monitor, give it admin rights if you want to use it's
controls to start and stop the service, and make sure it's operation is
tied to the service and it's reporting properly. Then, you can enable
statistics, etc. Once it's running OK, you can stop the service, edit
the config file to tweak the server settings, and restart the service.
Make sure the setup screen says to start the service automatically if
you want it to do that. It will say manually while it's stopped, but
should go back to automatically once it's started again. If anyone
needs help setting this up, I'd be glad to help. I think this is the
best time setting solution I've seen for Windows. I like it better than
the NIST client I'd been running before.
Sincerely,
Ron
---------------------------------
Links to screen shots of the Windows NTP client:
http://dl.dropbox.com/u/9879631/ntp-mon01.jpg
http://dl.dropbox.com/u/9879631/ntp-mon02.jpg
http://dl.dropbox.com/u/9879631/ntp-mon03.jpg
http://dl.dropbox.com/u/9879631/ntp-mon04.jpg
http://dl.dropbox.com/u/9879631/ntp-mon05.jpg
http://dl.dropbox.com/u/9879631/ntp-mon06.jpg
http://dl.dropbox.com/u/9879631/ntp-mon07.jpg
http://dl.dropbox.com/u/9879631/ntp-mon08.jpg
http://dl.dropbox.com/u/9879631/ntp-mon09.jpg
http://dl.dropbox.com/u/9879631/ntp-mon10.jpg
http://dl.dropbox.com/u/9879631/ntp-mon11.jpg
http://dl.dropbox.com/u/9879631/ntp-mon12.jpg
http://dl.dropbox.com/u/9879631/ntp-mon13.jpg
http://dl.dropbox.com/u/9879631/ntp-mon14.jpg
http://dl.dropbox.com/u/9879631/ntp-mon15.jpg
http://dl.dropbox.com/u/9879631/ntp-mon16.jpg
--
(PS - If you email me and don't get a quick response, you might want to
call on the phone. I get about 300 emails per day from alternate energy
mailing lists and such. I don't always see new messages very quickly.)
Ron Frazier
770-205-9422 (O) Leave a message.
linuxdude AT c3energy.com
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