Hi Didier,

On 28/4/20 14:50, Didier Kryn wrote:
>     Thanks Aitor for having investigated this and found a solution,
> though I'm not sure the cause of the delay if fully understood.
>
>     The interfaces file describes actions which ifupdown performs  to
> set interfaces up and down, plus two special clauses "auto" and
> "allow-hotplug", which tell it which interfaces to set up
> automatically respectively at start-up or when the interface is
> plugged in (eg USB-Ethernet or USB-wifi interface). In the case of the
> loopback interface, "auto" is always fine because it isn't a hardware
> interface; in the case of other interfaces, "auto" works only if the
> interface is hard-wired and "allow-hotplug" works as well if it is
> hard-wired or hot-plug; this is why "auto" is deprecated in the
> installers except for lo.
>
>     In the case of a  server, you generally want all interfaces
> (connected to different networks) to be brought up at start-up,
> therefore you just need "allow-hotplug" for all interfaces. In the
> case of a laptop with both a wifi and an Ethernet interface you
> generally do not want both interfaces to be used in the same time
> because they both play the role of the primary interface connected to
> the LAN, with identical configuration (typically "inet dhcp"). This is
> why you don't want ifupdown to start both; instead you need some tool
> able to detect if an ethernet cable is plugged in. When an ethernet
> cable is plugged in, this tool will tell ifupdown to configure the
> Ethernet interface and deconfigure the Wifi. If the cable is plugged
> out, it will tell it to do the opposite. I know two such tools:
> ifplugd and netplug. But there shouldn't be "auto" or "allow-hotplug"
> stanzas in the interface file in this case; their only effect is to
> cause a delay at start-up.
>
>     In summary "auto" and "hotplug" assume that the interface can be
> configured. If you cannot assume it blindly, dont put them and install
> ifplugd or netplug. And this is the general case of a laptop. I
> understand that it would add more complexity to the installer to
> decide what to put in the interfaces file and it probably should not
> force the installation of ifplugd or netplug.

How well explained!

>     I guess the policy in Debian is to install network-manager and not
> ifupdown. I don't know what ifupdown2 does;it is incompatible with
> ifplugd. Maybe it is able to detect by itself that an Ethernet cable
> is connected.

I'm not pretty sure at this point. Maybe ifplugd breaks with ifupdown2
due to its dependency on ifupdown, being this second one more veteran
than the first one. I have no arguments to affirm wether ifplugd works
or not with ifupdown2 because the debian/control file doesn't allow this
blend. Maybe defining something like "Depends: ifupdown | ifupdown2,
...", in the same way than the ifupdown packaging allows to use
different dhcp clients...

Aitor.