modem-manager causes slow shutdown/reboot

Status changed to 'Confirmed' because the bug affects multiple users.

I've also seen that it seems like modemmanager initializes at shutdown. It is easier to see if you disable the splash/quiet boot options.

As always, debug logs of MM would help a lot.

  sudo /usr/sbin/ModemManager --debug > /home/yourself/MM.log

In that way you can safely reboot and then check the MM log afterwards.

In Ubuntu that will be:

sudo /usr/sbin/modem-manager --debug > /home/$HOME/MM.log

Just be aware that first you must run "sudo stop network-manager" and "sudo killall modem-manager".

Okay, here is what I got from the debug:

modem-manager[2887]: <info> [1351082877.649683] [main.c:167] main(): ModemManager (version 0.6.0.0) starting...
modem-manager[2887]: <info> [1351082877.658050] [mm-manager.c:158] found_plugin(): Loaded plugin 'Huawei'
modem-manager[2887]: <info> [1351082877.658128] [mm-manager.c:158] found_plugin(): Loaded plugin 'Sierra'
modem-manager[2887]: <info> [1351082877.658149] [mm-manager.c:158] found_plugin(): Loaded plugin 'Option'
modem-manager[2887]: <info> [1351082877.658168] [mm-manager.c:158] found_plugin(): Loaded plugin 'X22X'
modem-manager[2887]: <info> [1351082877.658185] [mm-manager.c:158] found_plugin(): Loaded plugin 'SimTech'
modem-manager[2887]: <info> [1351082877.658202] [mm-manager.c:158] found_plugin(): Loaded plugin 'Wavecom'
modem-manager[2887]: <info> [1351082877.658219] [mm-manager.c:158] found_plugin(): Loaded plugin 'Ericsson MBM'
modem-manager[2887]: <info> [1351082877.658237] [mm-manager.c:158] found_plugin(): Loaded plugin 'Nokia'
modem-manager[2887]: <info> [1351082877.658256] [mm-manager.c:158] found_plugin(): Loaded plugin 'Linktop'
modem-manager[2887]: <info> [1351082877.658274] [mm-manager.c:158] found_plugin(): Loaded plugin 'Gobi'
modem-manager[2887]: <info> [1351082877.658291] [mm-manager.c:158] found_plugin(): Loaded plugin 'Longcheer'
modem-manager[2887]: <info> [1351082877.658308] [mm-manager.c:158] found_plugin(): Loaded plugin 'AnyData'
modem-manager[2887]: <info> [1351082877.658326] [mm-manager.c:158] found_plugin(): Loaded plugin 'Samsung'
modem-manager[2887]: <info> [1351082877.658344] [mm-manager.c:158] found_plugin(): Loaded plugin 'Option High-Speed'
modem-manager[2887]: <info> [1351082877.658362] [mm-manager.c:158] found_plugin(): Loaded plugin 'MotoC'
modem-manager[2887]: <info> [1351082877.658379] [mm-manager.c:158] found_plugin(): Loaded plugin 'ZTE'
modem-manager[2887]: <info> [1351082877.658396] [mm-manager.c:158] found_plugin(): Loaded plugin 'Novatel'
modem-manager[2887]: <info> [1351082877.658415] [mm-manager.c:158] found_plugin(): Loaded plugin 'Iridium'
modem-manager[2887]: <info> [1351082877.658432] [mm-manager.c:158] found_plugin(): Loaded plugin 'Cinterion'
modem-manager[2887]: <info> [1351082877.658450] [mm-manager.c:158] found_plugin(): Loaded plugin 'Generic'
modem-manager[2887]: <info> [1351082877.658469] [mm-manager.c:210] load_plugins(): Successfully loaded 20 plugins
modem-manager[2887]: <debug> [1351082877.658805] [mm-manager.c:1057] mm_manager_start(): Starting device scan...
modem-manager[2887]: <debug> [1351082877.661379] [mm-manager.c:875] device_added(): (tty/ttyS0): port's parent platform driver is not whitelisted
modem-manager[2887]: <debug> [1351082877.661600] [mm-manager.c:875] device_added(): (tty/ttyS1): port's parent platform driver is not whitelisted
modem-manager[2887]: <debug> [1351082877.661804] [mm-manager.c:875] device_added(): (tty/ttyS10): port's parent platform driver is not whitelisted
modem-manager[2887]: <debug> [1351082877.661951] [mm-manager.c:875] device_added(): (tty/ttyS11): port's parent platform driver is not whitelisted
modem-manager[2887]: <debug> [1351082877.662195] [mm-manager.c:875] d...

I cannot see any request to shutdown ModemManager in the logs... did you really shutdown/reboot your PC after running MM in debug mode?

It might be that what I am seeing is just the shutting down of modemmanager (disconnecting, disabling modems etc.), which sometimes could take some time.

As far as I can tell modem-manager keeps getting respawned (pid changes) on my machine (always as a child of init, pid 1).

I tried to:
1) service modem-manager stop
2) kill the process with killall
3) comment the start line in /etc/init/modemmanager.conf and reboot

Whatever I did there was always a /usr/sbin/modem-manager running... upstart bug?

Purging the package from the system did improve the shutdown time noticeably.

Yes, modemmanager process is respawned when there is some client that need it and it is not running. That means that you will need to shut down network-manager to avoid it starting again. Does that improve shutdown time?

Interesting, thank you again, now I see that network-manager spawns modem-manager trough D-bus.
But then what's /etc/init/modem-manager.conf meant for?
Without waiting an answer I've tried to remove it and things just seemed to get better.

As you suggested shutting down network-mamanger (which anyway takes whole 5 seconds to complete on my little eeepc) before shutdown made it as fast as it were with precise.

Tring to anticipate it's shutdown I've ended modifying both networking.conf and network-manager.conf to stop also on "runlevel [06]". I don't pretend this to be the solution but it helped somehow my shutdown to be faster and without unnecessary restarts of modem-manager.

Can it be that the stop of Network Manager is triggered to late in the chain, making services crash because network is already unavailable and then get started over and over?

I fixed problem by adding this line to my /etc/init/ modem-manager.conf :

stop on runlevel[0]

Now my shutdown time has been brought down to nearly 5 seconds (from 15-20 seconds).