ModemManager auto reconnect

[Dan Williams]

On Wed, 2016-02-10 at 09:10 +1100, Brendan Simon (eTRIX) wrote:
> 
> On 10/02/2016 3:39 AM, Dan Williams wrote:
> > On Tue, 2016-02-09 at 11:27 +1100, Brendan Simon (eTRIX) wrote:
> > > On 9/02/2016 9:08 AM, Dan Williams wrote:
> > > > On Tue, 2016-02-09 at 07:31 +1100, Brendan Simon (eTRIX) wrote:
> > > > > I have a number or remotely deployed arm embedded linux
> > > > > systems
> > > > > that
> > > > > uses a 3G modem via USB to post http information once per
> > > > > second.
> > > > >  The
> > > > > modem goes down from time to time.  One reason is we assert
> > > > > the
> > > > > power
> > > > > reset line on the modem once a day (as I've been told that
> > > > > the
> > > > > modems
> > > > > need to be reset periodically, otherwise functionality
> > > > > degrades
> > > > > or
> > > > > eventually lost).  The other reasons I am not sure of
> > > > > (service
> > > > > provider
> > > > > initiated?  bugs in the application code?
> > > > > 
> > > > > The modem can be off for many hours before eventually
> > > > > reconnecting
> > > > > (possibly by watchdog reboot) which is not acceptable for our
> > > > > real
> > > > > -time
> > > > > monitoring application.
> > > > > 
> > > > > Does MM automatically try to re-establish a connection if it
> > > > > sees
> > > > > the
> > > > > connection go down, or the modem is reset?
> > > > > 
> > > > > Are there recommended or suggested MM settings such that MM
> > > > > will
> > > > > continually try to reconnect if the modem goes down then back
> > > > > up?
> > > > This is left up to the connection manager that controls
> > > > ModemManager
> > > > and tells it to connect.  So whatever you're using to tell
> > > > ModemManager
> > > > to start the data connection, that's the thing that would
> > > > monitor
> > > > for
> > > > the modem being disconnected and periodically restart the data
> > > > connection.
> > > I created a NetworkManager broadband connection in a Debian
> > > virtual
> > > machine with a modem connected (dev kit).  I then copied the file
> > > that
> > > was created
> > > (/etc/NetworkManager/system-connections/telstra-mobile-broadband-
> > > 1)
> > > into
> > > my build system which will populate my target rootfs for the
> > > embedded
> > > system.
> > > 
> > > I found that the modem was not coming up at boot, but would come
> > > up
> > > if I
> > > used the `nmtui-connect` utility to activate the connection.  A
> > > systemd
> > > service was created to bring up the modem at boot time (a one-
> > > shot
> > > script, which brings the modem down then up then calls `nmcli d
> > > connect
> > > cdc-wdm0`).
> > > 
> > > The scirpt works but I'm not sure if it's the `right way` to get
> > > the
> > > modem up automatically.  One interesting thing which may be a
> > > clue is
> > > that the modem connection does not appear in the `nmtui-edit`
> > > utility,
> > > but does appear in the `nmtui-connect` utility.  Is this expected
> > > ? 
> > > Also the LAN connection shows up in both utilities but there a
> > > connection file does not exist in /etc/NetworkManager/system
> > > -connections/
> > > 
> > > I presume NetworkManager is starting and managing the connection,
> > > yes? 
> > > How do I get it to auto-reconnect when the connection goes down
> > > or is
> > > not available?  We are looking at running a custom script invoked
> > > via
> > > cron every minute, but that seems a bit hacky.
> > What version of NM?  There have been improvements to the
> > autoconnect
> > logic for WWAN recently in NM, especially if the SIM has a PIN
> > enabled.
> >  Aside from bugs, we would expect NM to periodically retry the
> > connection if it fails.
> 
> The following Debian Jessie packages are installed.
>     network-manager                0.9.10.0-7
>     modemmanager                   1.4.0-1  
> 
> There is no PIN enabled on the SIM cards.
> 
> I suspect that there is something not configured properly with NM as
> it
> doesn't recognise that I have a broadband connection if I invoke
> `nmtui-edit`.  However it does know about the connection if I invoke
> `nmtui-connect`.

nmtui in 0.9.10 may just not know how to edit a WWAN connection, but it
can certainly start/stop any connection.

> Is the file in /etc/NetworkManager/system-connections/ all that I
> need,
> or is there another NM config file that needs to know about the
> connection?

No, that should be all you need.  Make sure it has 'autoconnect=true'
in the [connection] section though.

> Is the `uuid` field in the connections file significant?
> Does it need to match something on my system?
> The `uuid` field is set to the same on all the boxes.

No, UUID wouldn't be related to this.  It's just a connection
identifier and has no effect on whether the connection is retried or
not.

I just tried out reconnect on NM 0.9.10.2 and it appears to work, at
least for the initial tries.  I disconnect the antenna and wait for the
connection to drop, and NM does attempt to reconnect a couple times,
and then you should see "Disabling autoconnect for connection XXXXX".
 That will last for about 5 minutes (AUTOCONNECT_RESET_RETRIES_TIMER),
at which point NM will try another few times to connect.

If that's not the behavior you're seeing, could you reply with
NetworkManager's log output so we can diagnose further?

Dan