Re: ntp rant
- From: Tobias Brox <tobias@xxxxxxxxxxxxxx>
- Date: Thu, 12 Apr 2007 21:59:46 +0000 (UTC)
I hate NTP.
And I love it ;-)
It does a simple job in such a ridiculously arcane way.
It's overly complex, and difficult to set up ... I absolutely agree on
that. ntp by multicast or broadcast sounds like cool features, but I
never got them to work. It's overkill for adjusting a simple desktop
clock, but nowadays the resource usage is insignificant compared to
the average b/w, cpu, mem etc a normal desktop computer is equipped
Setting it up with plenty of redundant time servers, one can just let
it run and forget about it. (At our servers, I have scripts graphing
the time differences and sending alarms, though). If the clock gets
seriously out of sync, one needs to restart it. One would also need
to configure the computer to adjust the hw clock after the system
clock, particularly on a laptop that is frequently shut down. I think
the system clock should be in UTC, particularly in countries having
daylight saving time, or at laptops that are frequently passing
I've been using it for years and still don't even know how to determine
whether it's doing anything at all. Just because nptq -p spouts its
usual gibberish (not documented in the manpage of course), don't assume
your clock is sync'd.
The gibberish is well documented, and the number one most important
column is "offset", which is the difference between your clock and the
other servers, in milliseconds.
I don't remember where it is documented, probably in the html
documentation shipped with ntp, though nowadays google is often easier
than searching for documentation on the harddisk ...
Informative error messages? Forget it! "no
server suitable for synchronization found." Wow, a single unvarying
sentence that describes every possible issue! Check the syslog for more
and you'll probably find "ntpd exiting." Oh, now I understand!
I agree that this is a problem, I've also experienced problems like
this. There is a debug mode, but not much helpful.
Also, I always wonder for how long I have to wait from the ntp deamon
is started and until the clock actually gets synced.
Isn't there something better? I'm perfectly willing to sacrifice a
few milliseconds of accuracy here or there if that's what it takes.
There is always openntp - my colleague installed it at our servers,
but we had to throw it out of production. Maybe it was just
misconfigured, but our server clocks was really fluctuating. While we
don't need millisecond precision, I found that 250 ms difference
actually can be too much in some circumstances. One usually wouldn't
bother on a laptop, though.
Moreover, it was stopping up very frequently, and (before we got the
alarm scripts installed) the servers could really drift unacceptably much
before we discovered it. I think that while ntpd accepts a slack of
several minutes (half an hour?) openntpd only accepts some seconds,
and sometimes it was not capable of keeping the clocks well enough in
sync. Well, may have been a configuration issue, but I concluded ntpd is
much better than openntpd - which is kind of sad, since I generally
like things to be "open".
For a desktop computer, a cronscript syncing the clock with ntpdate
could be considered - anyway, since memory and cpu is cheap nowadays,
I prefer to have a fire-and-forget daemon there watching the clock.
Tobias Brox, 69°42'N, 18°57'E
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