questo il syslog dopo la riconnessione fallita:
Aug 31 18:57:25 linux pppd[2604]: Using interface ppp0
Aug 31 18:57:25 linux pppd[2604]: Connect: ppp0 <--> /dev/ttyUSB0
Aug 31 18:57:25 linux pppd[2604]: Modem hangup
Aug 31 18:57:25 linux pppd[2604]: Connection terminated.
Aug 31 18:57:25 linux NetworkManager[916]: <info> Activation (ttyUSB0) Stage 4 of 5 (IPv4 Configure Timeout) scheduled...
Aug 31 18:57:25 linux NetworkManager[916]: <info> Activation (ttyUSB0) Stage 4 of 5 (IPv4 Configure Timeout) started...
Aug 31 18:57:25 linux NetworkManager[916]: <info> (ttyUSB0): device state change: ip-config -> failed (reason 'ip-config-unavailable') [70 120 5]
Aug 31 18:57:25 linux NetworkManager[916]: <warn> Activation (ttyUSB0) failed.
Aug 31 18:57:25 linux modem-manager[912]: <info> (ttyUSB0) closing serial port...
Aug 31 18:57:25 linux modem-manager[912]: <info> (ttyUSB0) serial port closed
Aug 31 18:57:25 linux modem-manager[912]: <info> Modem /org/freedesktop/ModemManager/Modems/0: state changed (connected -> disconnecting)
Aug 31 18:57:25 linux modem-manager[912]: <info> Modem /org/freedesktop/ModemManager/Modems/0: state changed (disconnecting -> connected)
Aug 31 18:57:25 linux NetworkManager[916]: <info> Activation (ttyUSB0) Stage 4 of 5 (IPv4 Configure Timeout) complete.
Aug 31 18:57:25 linux NetworkManager[916]: <info> disconnect failed: (32) The serial port is not open.
Aug 31 18:57:25 linux NetworkManager[916]: <info> (ttyUSB0): device state change: failed -> disconnected (reason 'none') [120 30 0]
Aug 31 18:57:25 linux NetworkManager[916]: <info> (ttyUSB0): deactivating device (reason 'none') [0]
Aug 31 18:57:25 linux NetworkManager[916]: nm_system_iface_flush_routes: assertion `ifindex > 0' failed
Aug 31 18:57:25 linux NetworkManager[916]: nm_system_iface_flush_addresses: assertion `ifindex > 0' failed
Aug 31 18:57:25 linux NetworkManager[916]: SCPlugin-Ifupdown: devices removed (path: /sys/devices/virtual/net/ppp0, iface: ppp0)
Aug 31 18:57:26 linux pppd[2604]: Exit.


questo il comando che mi hai detto tu:

tojo72@linux:~$ ps aux | grep NetworkManager
root 916 0.0 0.0 259940 5460 ? Ssl 18:20 0:00 NetworkManager
tojo72 2628 0.0 0.0 35552 928 pts/0 S+ 18:58 0:00 grep --color=auto NetworkManager
tojo72@linux:~$