Re: "Downing" interfaces on reboot cmd or a panic

On Tue, Aug 25, 2026 at 3:29 PM Karl Denninger <karl@denninger.net> wrote:

> None of the above do.
>
> "shutdown -r" does, as it calls back through the "stop" chain in netif.
> But a reboot command (or kernel panic) does not; the latter obviously can't
> and the former doesn't go through any of those nicities at all.
>
> I've never seen this cause trouble on a LAN but when the machine in
> question is an Internet gateway in some cases ONTs in particular want to
> see the interface carrier disappear specifically to tell it that the line
> was reset.  If it doesn't then on machine restart it may not remain
> properly associated with the ONT and thus you get no -- or partial --
> connectivity.
>
> On a cold boot this isn't an issue because the interface was never up in
> the first place, but on restarts it can be.  I've got an ISP here that
> sometimes will not restore connectivity properly in this instance, but on a
> shutdown (or power cycle) it never has a problem -- and it appears, from
> watching the interface LEDs, that the lack of carrier-toggling is
> responsible.  While an "attended" restart is easy ("don't use reboot")
> what's not-so-much is if the machine takes a panic while nobody is there to
> attend it and connectivity does not come back up.
>
> I'm curious if anyone has thought about how this might be better handled
> (e.g. is this something that perhaps the startup sequence should have a
> flag for and, if its present, then all interfaces are "down"ed first as a
> protective measure to force carrier off before being configured?)
>
> Thoughts?
>
Shouldn't the NIC drivers be doing this shutdown as part of their newbus
shutdown callbacks?

But also, I thought there was support for turning the 'reboot'  command
into 'shutdown -r' and moving the current functionality to 'reboot -f' or
'fastboot'... What ever happeend to that notion?

Warner