[ntp:questions] Local clock question with dialup connection

Nigel Henry cave.dnb at tiscali.fr
Thu Apr 19 23:15:10 UTC 2007


On Thursday 19 April 2007 23:38, David Woolley wrote:
> In article <200704191816.22365.cave.dnb at tiscali.fr>,
>
> cave.dnb at tiscali.fr (Nigel Henry) wrote:
> > failing to be found, and ntpd is not trying them again.  I presume a
> > server pool has many available servers, so if I have a server pool in
> > /etc/ntp.conf, does ntpd just keep on trying to get a response in this
> > case, like it tries the pool, doesn't get a response, tries again, no
> > response, tries again, and
>
> ntpd has no special code for handling server pools, nor does the operating
> system.  When ntpd starts, it spawns a name resolver process.  This looks
> up all the servers given by name in the configuration file and sends
> commands back to the main process to set the addresses of the servers.
>
> For each name it asks DNS.  As you have broken connectivity, the DNS name
> resolver times out without returning any members of the pool.  This is
> repeated in turn for each name until they all fail or the network
> comes up.  The requests will be done sequentially because one of the main
> reasons for using a separate process is that the standard resolver library
> is blocking.

Yeh thats pretty much the way I'm seeing it. FC6 seems to handle it ok when 
booting up with no Internet connection. That's with using 4.2.4p0-1.fc6, and 
"dynamic" added to each of the server lines in /etc/ntp.conf. I boot up FC6, 
then connect to the Internet, then run ntpq> pe, and 3 of the pools servers 
are listed, and one is soon maked as a system peer.

The problems are with FC2. I know it's old, but I still receive all my mail on 
it, and use it daily. I think what I really need is a script that detects 
when an Internet connection is up and running, then starts ntpd. I'm not too 
clever with scripts. I'll ask around, and see if some kind hearted scripter 
can suggest something.
>
> The nameserver is responsible for returning a random selection from the
> pool on each request, but it never receives any requests.
>
> If a member taken from the pool does not respond to NTP requests, a
> replacement will not be taken from the pool.  Instead, ntpd will just keep
> requesting the same server.
>
> To avoid this part of the problem, you should, from time to time,
> manually look up the addresses of the pool servers and put those into
> ntpd.conf, rather than use their names.

I noticed that as well. On one boot up of FC2 the only server listed was one 
using an IP address rather than a host name.
>
> Regarding startup scripts, as I already said, the ntpd Linux binaries can
> be used in many different distribution, and not all of them use the tactic
> that Red Hat use for finding, sequencing and running theirs.  It would be
> rude of the installer to dump an inappropriate file into /etc.

Yes I appreciate that.

I appreciate the response to this question. Thanks a lot.

Nigel.



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