I am having the same problem with my Dell optiplex GX620. The weird thing is that it does not happen everytime. Cannot find the relevant log, but is says:
NetworkManager: nm_dbus_signal_device_status_change: assertion `cb_data->data->dbus_connection' failed -- system hangs at shutdown https://bugs.launchpad.net/bugs/138691 You received this bug notification because you are a member of Ubuntu Bugs, which is the bug contact for Ubuntu. -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
