rc(8) script -- waiting for the network to become usable

[Garrett Cooper]

On Sun, Apr 18, 2010 at 4:24 PM, Andrew Reilly <areilly at bigpond.net.au> wrote:
> On Sun, Apr 18, 2010 at 02:37:27PM -0700, Jeremy Chadwick wrote:
>> I'd like to discuss the possibility of introduction of a new script into
>> /etc/rc.d base system a script, which when enabled, would provide a way
>> to wait until the IP networking layer (using ping(8)) is up and usable
>> before continuing with daemon startup.
>>
>> Let's discuss.  :-)
>>
>>
>> HISTORY
>> =========
>> The situation which brought this debacle to my attention:
>>
>> I found that on reboot of some of our systems, ntpdate (used to sync the
>> clock initially before ntpd would be started) wouldn't work.  The daemon
>> would report that it couldn't resolve any of the FQDNs within ntp.conf,
>> and would therefore act as a no-op before continuing on.
>
> By way of discussion, I'd just like to re-iterate what I
> said the first time around: it must be understood that this
> sort of thing is a (necessary) hacky-workaround that should
> ultimately be unnecessary.  In preference, we should work on
> the failing daemons or hassle up-stream daemon authors so
> that the daemons in question either (a) retry until they *do*
> get the information they're after or (b) fail properly, so
> that they can be restarted by an external process monitoring
> framework like sysutils/daemontools or launchd.  The reasoning
> is simple: network outage is something that can happen even
> after startup, and when network connectivity returns, the
> routing and addresses that are visible won't necessarily be the
> same.  Consider laptops that suspend, as a particular example.
> Or mobile devices that switch from wi-fi to cellular networking
> to no connectivity on a regular basis.  The "get it right at
> boot time" model is important and traditional, but (I think)
> a fragile and diminishing fraction of use cases.  Our rc-ng
> framework favours solution (a).  I'm more a fan of approach (b),
> myself: I use daemontools for many services, and I like the way
> that launchd works on my Mac laptops.

    I agree with Andrew. This is the model that Mac has been on for a
while now with launchd and this is the way that we should be migrating
towards (IMO) as it does a better job at detecting asynchronous system
events and could improve the overall init / rc model used in FreeBSD.
    What ever happened to this work: http://wiki.freebsd.org/launchd ?
I remember that Apple went in a more OSX centric set of APIs in
Leopard+, but it might be worthwhile to start with the older version
of launchd, and migrate from there.
Thanks,
-Garrett