dhcpcd-discuss

Hi Reto

On 05/05/2019 13:28, Reto Schneider wrote:
> I would like to get my embedded device to check for updates whenever its
> connectivity got changed (and the interface is up). For example, after
> the user has plugged in the Ethernet cable or the WLAN came up and an IP
> address and default gateway got assigned.
>
> Looking at $reason in dhcpcd-run-hook it seems to me that BOUND and
> BOUND6 is what I want to use for DHCP/DHCPv6 networks. However, only for
> IPv4 networks I can be (quite) sure that DHCP gets used. Not for IPv6 ones.
>
> It seems to me that I also have to trigger on ROUTERADVERT. However, my
> hook gets called every time my device receives a router advertisement
> and I do not know how to figure out if actually anything of relevance
> has changed regarding the networking topology.
>
> CARRIER together with a big-ish delay before starting the update would
> likely work, but is quite hackish.
>
> Is it possible to do achieve my obviously non-DHCP related goal using
> dhcpcd? If so, how?

Most simple test
cat /etc/dhcpcd.exit-hook

if $if_up || [ "$reason" = ROUTERADVERT ]; then
   do_your_update()
fi

Now that will fire whenever dhcpcd gets as valid lease or a router 
advertisement.
That might be far too frequent for your needs.

Antyhing *of relevance* that has changed could mean many things - for 
example has the hardware address of the default router changed? Are we 
running on wireless or wired?

I think the easiest solution would be to pull for an update via a cron job.

Roy