Re: setup a local ntp server on debian
On Wed, Sep 23, 2009 at 6:38 PM, <gcrimp@vcn.bc.ca> wrote:
> On Wed, Sep 23, 2009 at 02:58:59PM -0500, Israel Garcia wrote:
>> We've been increasing in numbers of debian lenny servers and they has
>> a cron.hourly as follow:
>>
>> #!/bin/bash
>> /usr/sbin/ntpdate -u swisstime.ethz.ch
>>
There are a number of issues with setting the clock this way. I
won't bother to list them, it's enought to say that this is vary
unlikely tobe safe.
ntpdate has been replaced with running ntpd with a flag that makes it
act like ntpdate. Setting the clock spontaniously, I.E. via
cron, can cause devide by zero errors in applications making /s
calcuations(where s1 == s2 when x = d1 - d2 / s1 - s2). You can
also have warnings in applicatiions that compair time stamps, like
tar's this file's time is in the future.
The correct way to set the clock with ntp is to run ntpd as a daemon,
question #3 below. If you wish you can have ntpd maintain a drift
file for use when there are no time sources(other then the system's
clock) avalible. It may also be possible, although not positivly
safe,to run ntpd for a few hours(8 to 20) every weekend to adjust
the clock. Every hour or day is to small a time to adjust the
clock reasonably, even if you did descide to run it 4 hours every
day... why bother to disable it the other 20 hours, %80 of the time?
>> We're planning to setup our NTP's servers only to serve our local
>> boxes. I've some questions for you:
>
> I recently set up an ntp server. It is one of the easiest
> protocols I've set up. Here are some links that I found
> useful when researching ntp:
>
> http://support.ntp.org/bin/view/Servers/WebHome
> http://geodsoft.com/howto/timesync/
> http://www.pool.ntp.org/
>
> This isn't all I looked at but it should get
> you started.
>
>
>>
>> 1. Which do you suggest to use? openntpd or ntp server?
>
> I used ntp.
>
>> 2. Can I setup redundancy with any of them?
>
> I think that is a fundamental principal of
> the protocol.
>
>> 3. What client should I use to synchronize other boxes clock? ntpdate
>> command or ntp daemon client?
>
> I used ntp on all the boxes. The box that serves as
> the server for my LAN gets it time from an ntp pool
> of servers. So it is acting as both client as server
> without any additional setup. Of course this means
> that there is no redundancy locally. Local
> redundancy is possible, but my reading lead me to
> conclude that for my purposes, it was not necessary.
>
> I used netselect to figure out which pool would give
> me the best average response time over many tries on
> three different occasions.
>
>> 4. Should I use a local NTP or do you suggest all client synchronize
>> to an external server?
>
> Some of the docs above helped my decide that setting up a local
> server provided adequate synchronization. No need to burden remote
> servers to make questionable gains in clock accuracy.
>
>
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