[opensuse] Re: ntp and wireless
j debert wrote:
Why do you need ntp?
Is the system clock severely sloppy about keeping correct time?
Yes. PC-class hardware is notoriously bad and system times will vary by seconds or minutes within a few days.
Is there something critical that requires zero delta time with some other system(s)?
Not zero, but also not beyond seconds. E.g., time stamps in Kerberos tickets, correlation of log entries.
A script to periodically test the network connection and run netdate or rdate when the network is up works just fine.
No. It steps the time, whereas ntp *adjusts the clock*. Many systems, in particular databases, don't like stepping, also all applications that use time stamps to order events. That's a problem especially if the time is stepped backward and some point in time happens to occur twice. Do yourself a favor and run ntp. In the end, it's even easier than self-written cron jobs with netdate. Use what's available in your distribution, don't invent such stuff anew -- there are already too many people running around with a hexagon in their hand shouting "I invented the wheel!". Joachim -- =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Joachim Schrod Email: jschrod@acm.org Roedermark, Germany -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On Monday, 2009-11-02 at 09:02 +0100, Joachim Schrod wrote:
A script to periodically test the network connection and run netdate or rdate when the network is up works just fine.
No. It steps the time, whereas ntp *adjusts the clock*. Many systems, in particular databases, don't like stepping, also all applications that use time stamps to order events. That's a problem especially if the time is stepped backward and some point in time happens to occur twice.
ntp is the best tool if you have continuous network access. If you don't, you need an alternative, and a cron job is une of those. Notice that if you start/ the ntp service any time, it does jump at the start of the script. - -- Cheers, Carlos E. R. -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (GNU/Linux) iEYEARECAAYFAkr0fWgACgkQtTMYHG2NR9VvTQCcCkwhjPX1vJZDX89iM9FMNsID o+cAn3LAC7QieaYzx4Pail+2kpiiV3N7 =oSy3 -----END PGP SIGNATURE----- -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org
On Fri, 6 Nov 2009 20:47:48 +0100 (CET), you wrote:
ntp is the best tool if you have continuous network access. If you don't, you need an alternative, and a cron job is une of those.
But the better one in that case is to get a time source like a GPS clock and use that as external clock for ntpd. Philipp -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On Saturday, 2009-11-07 at 00:14 +0100, Philipp Thomas wrote:
On Fri, 6 Nov 2009 20:47:48 +0100 (CET), you wrote:
ntp is the best tool if you have continuous network access. If you don't, you need an alternative, and a cron job is une of those.
But the better one in that case is to get a time source like a GPS clock and use that as external clock for ntpd.
That is an overkill. If there is no continuous network, the machine is not part of a permanent network, there is no need to be in sync with anyone. Why would that machine need a clock source correct to the centisecond? If is part of local network not connected to internet, the case is a bit different, of course: but only local sync is really required, not more. Like, for example, why would a home user need an exact clock on his computer? Our watches, alarm clocks, kitchen clocks, oven clocks... none of them are in sync. Computers are not that different. The video recorder clock is in sync: that's different. - -- Cheers, Carlos E. R. -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (GNU/Linux) iEYEARECAAYFAkr0xrkACgkQtTMYHG2NR9UelgCfR11JW6lIRMXj7n6pkZaBgZbw RyUAoJcx9xfQVYb5Jg9gtN7eacYdABV/ =Dl7g -----END PGP SIGNATURE----- -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org
Joachim Schrod さんは書きました:
Yes. PC-class hardware is notoriously bad and system times will vary by seconds or minutes within a few days.
And that's why there's adjtime. Or by "system clock" do you mean the hardware clock? That's not what I asked about. Outside of microsoft world, "system clock" means that little timekeeper in the *nix kernel. You might find that hardware clocks are much more accurate than the original 5150 and 5160 clocks, if you bothered to check. To keep talking about how bad PC hardware clocks _were_ is useless. It's like talking about all the wood you have to use for your central heating. Times have changed. So has hardware. You erred in your assumptions. Let's adjust them: 1. the cronjob runs every 2 months. 2. The script is 25 or so years old, predating even RFC958. 3. The wheel was decahexagonal. Who is prescient enough to see the need to prepare to reinvent your wheel 25 years later? Or was that merely a bit of grandstanding? I don't need microsecond resolution yet. I already said that my clocks are accurate. -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org
On Friday 06 Nov 2009 21:28:10 j debert wrote:
Joachim Schrod さんは書きました:
Yes. PC-class hardware is notoriously bad and system times will vary by seconds or minutes within a few days.
I don't need microsecond resolution yet. I already said that my clocks are accurate.
Well sorry to say but you are fooling yourself very heavily there , If the acuracy with which the PC clock system keeps time the the world must be so far out of Sync it is untrue when you have a 09:00 appointment what time do you leave 12:00 the pervious day , PC clocks are pretty pi** poor to put it mildly Pete . -- Powered by openSUSE 11.2 Milestone 2 (x86_64) Kernel: 2.6.30-rc6-git3-4- default KDE: 4.2.86 (KDE 4.2.86 (KDE 4.3 >= 20090514)) "release 1" 08:34 up 18:00, 3 users, load average: 0.09, 0.04, 0.01
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On Sunday, 2009-11-08 at 08:38 -0000, Peter Nikolic wrote:
On Friday 06 Nov 2009 21:28:10 j debert wrote:
Joachim Schrod さんは書きました:
Yes. PC-class hardware is notoriously bad and system times will vary by seconds or minutes within a few days.
I don't need microsecond resolution yet. I already said that my clocks are accurate.
Well sorry to say but you are fooling yourself very heavily there , If the acuracy with which the PC clock system keeps time the the world must be so far out of Sync it is untrue when you have a 09:00 appointment what time do you leave 12:00 the pervious day , PC clocks are pretty pi** poor to put it mildly
No, you are wrong. The PC system clock is quite correct and stable. It drifts, yes, but the drift is usually constant and can be accounted for in the kernel. This is a known fact and published, I think in the ntp docs. It is based in a quartz xtal, after all... random errors can come from missed interrupts, and there are not that many (and I believe modern hardware can make for those missed timer interrupts by looking at other internal timers). Even ntpd is not continuously touching the clock. It looks, it may adjust the drift a bit, and then may not look again for another hour. - -- Cheers, Carlos E. R. -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (GNU/Linux) iEYEARECAAYFAkr2xCEACgkQtTMYHG2NR9WGvQCaA6d9SqQNxSuH7/4uUTSBSv5p Kn8An3Wlfz7rJX5DohqUovWixuBHShPw =rkjW -----END PGP SIGNATURE-----
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 j debert wrote:
I don't need microsecond resolution yet. I already said that my clocks are accurate.
Rather reminds me of the old schoolboy question... Which clock gives the more correct time, the clock that has stopped, or the clock that looses a microsecond an hour :-) (You also seem to be confused about accuracy and precision but that is different issue... ). - -- ============================================================================== I have always wished that my computer would be as easy to use as my telephone. My wish has come true. I no longer know how to use my telephone. Bjarne Stroustrup ============================================================================== -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (GNU/Linux) Comment: Using GnuPG with SUSE - http://enigmail.mozdev.org/ iEYEARECAAYFAkr2oOYACgkQasN0sSnLmgIHyACeOktTs3q2XF36u0BdgwJ7pMYI uOEAoL3fYwdpoxia/cS/3WtY40YiQMDA =It9d -----END PGP SIGNATURE----- -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org
participants (6)
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Carlos E. R. -
G T Smith -
j debert -
Joachim Schrod -
Peter Nikolic -
Philipp Thomas