Running a command when a specific interface is created or destroyed

[Julian H. Stacey]

Warren Block wrote:
> On Thu, 24 Apr 2014, Rolf Nielsen wrote:
> 
> > Hi,
> >
> > I use my phone's 3G/4G connection to connect my computer to the
> > internet. With the help of the urndis driver, it comes up as ue0.
> > However, if I reboot the computer, the phone automatically disables USB
> > tethering, and I can't re-enable it until the boot is complete.
> >
> > Being somewhat paranoid, I use an OpenVPN service, and I want the cilent
> > to start automatically. I obviously can't set it to start from rc.conf,
> > as I can't log in to the server before I have an internet connection.
> >
> > So, is there a way to start the OpenVPN client automatically upon
> > creation of the ue0 interface? E.g. can dhclient be set up to run the
> > openvpn start script after it has given ue0 an IP address? And is there
> > a way to automatically stop the openvpn client if ue0 is destroyed, e.g.
> > if I disconnect my phone from the computer?
> 
> devd(8) can do that.  Look at /etc/devd.conf for some examples, and 
> devd.conf(5) for more detail.

Yes, devd & its conf are very useful.


> > So, is there a way to start the OpenVPN client automatically upon
> > creation of the ue0 interface?

Yes, Example: I automatically fetch a password (if environment is
secure) to gbde decrypt & mount a UFS when a USB stick is attached.
http://www.berklix.com/~jhs/src/bsd/fixes/FreeBSD/src/jhs/etc/devd/berklix.conf
See lines beginning: gbde attach

On detach, closing processes or unmounting file systems Before a
device disappears is more problematic, as devd only gets nudged after.
I suppose if a VPN has a watchdog/ keepalive, no problem.
(For my crypted UFS, I should config AMD to umount my /media/* on
timeout, [& remount on demand]).

Cheers,
Julian
-- 
Julian Stacey, BSD Unix Linux C Sys Eng Consultant, Munich http://berklix.com
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