Is there an way for a program to know when the list of network interfaces has changed (without rescanning them)?

[Eugene Grosbein]

29.07.2019 12:35, Yuri wrote:

> I am asking because wireshark doesn't sense the interface list changes, and it just always shows the list from the time it was launched .

There is a way as we have devd(8) reading kernel-generated events and running commands in response.
Look at default /etc/devd.conf rules for example:

notify 0 {
        match "system"          "IFNET";
        match "subsystem"       "!(usbus|wlan)[0-9]+";
        match "type"            "ATTACH";
        action "/etc/pccard_ether $subsystem start";
};

Quoting devd(8) manual page:

>      Since devctl(4) allows only one active reader, devd multiplexes it,
>      forwarding all events to any number of connected clients.  Clients
>      connect by opening the SOCK_SEQPACKET UNIX domain socket at
>      /var/run/devd.seqpacket.pipe.

We have bsnmpd(1) in base system and its module usr.sbin/bsnmpd/modules/snmp_hostres
acting as client of devd, for example.