[PATCH 0/2] ntpd: retry name-resolution until success

[Rich Felker]

On Thu, Feb 11, 2016 at 05:56:06AM +0100, Denys Vlasenko wrote:
> On Thu, Feb 4, 2016 at 2:43 PM, Mark O'Donovan <shiftee at eircom.net> wrote:
> > This is an attempt to fix bug 8131:
> >   ntpd: should retry on name resolving error
> 
> Should it?
> Why doesn't ping do this? telnet? netcat? No network utility does this.
> Adding it to ntpd only would be inconsistent.

Because ping, telnet, and netcat are not daemons. A daemon should
respond gracefully to transient failures rather than aborting.

> I can see why this request comes specifically for ntpd. It is often started
> early at boot. Sometimes, network isn't up for some tens of seconds
> after boot, so ntpd fails to resolve names.
> 
> There are other ways to fix this.
> An utterly simplistic one would be to delay ntpd startup by, say, 20 seconds.

That's utterly broken. You end up with an invalid or badly-wrong
clock for the first 20 seconds after boot, which could lead to all
sorts of problems with timestamps.

> A slightly better one is to restart ntpd when it fails.

I don't see how this is any better than having it retry internally.
It's probably more work to implement and yields worse behavior.

Rich