Re: Interactions with ModemManager

[Dan Williams <dcbw redhat com>]

On Fri, 2017-04-21 at 11:32 +0100, Colin Helliwell wrote:
> > On 20 April 2017 at 17:28 Dan Williams <dcbw redhat com> wrote:
> >
> > On Mon, 2017-04-10 at 14:40 +0100, Colin Helliwell wrote:
> >
> > > A couple of things I've noticed in integrating NM with
> > > ModemManager:
> > >
> > > 1.  It seems that eth0 doesn't come up - i.e. dhcp client not
> > > fired
> > > off - until MM has done it's startup operations on the GSM modem.
> > > It
> > > so happens that my GSM has a long power-on pause, and that is
> > > holding
> > > up the system's eth network start-up too. Not a huge problem as a
> > > hyper-fast startup isn't needed, but not ideal..
> >
> > Missed this message... This may be due to NM's "startup" function,
> > where it waits for all interfaces that exist at startup to settle
> > before it tries to do anything with them. This tries to ensure that
> > composed devices (eg, bonds, bridges, teams, etc) have all the
> > components they need at startup.
> >
> > So yeah, that could prevent things from happening if the GSM modem
> > takes a long time to power on. You might be able to work around
> > this
> > by setting the NM "wwan enabled" property to "off" and then having
> > scripts or something flip that on later? A dispatcher script could
> > do
> > that perhaps.
> >
> > > 1.  Even after the initial 'query' start-up on the GSM, NM seems
> > > to
> > > leave it enabled (as per mmcli -m 0), rather than leaving it
> > > disabled
> > > until called upon (with a nmcli conn up XX)
> >
> > NM has the 'wwan-enabled' option which controls whether it powers
> > up
> > modems on start. If that option is off, NM will leave them in
> > 'disabled' state until the 'nmcli con up XXX'.
> >
> > Try setting 'nmcli radio wwan off', ensuring the modem is disabled
> > in
> > MM, then restarting NM. Does that keep the modem disabled?
>
> Just been having a try-out with that control. I see that the state
> persists across reboot - is there a way to force a particular bootup
> setting?

Yeah, you can twiddle that knob before NM starts in
/var/lib/NetworkManager/NetworkManager.state as you wish:

[main]
WWANEnabled=true   (or "false")

Just create the file if it doesn't exist, or use sed or something to
modify the value.  You could also change it with 'nmcli' at any point
during NM startup to, and NM should do the right thing.

Dan