To configure my RaspberryPi 4 to use a UBlox SARA-U201 4G USB Modem I used nmcli and mmcli. I connects after a minute after each boot now: :~ $ mmcli -m 0 -------------------------- General | dbus path: /org/freedesktop/ModemManager1/Modem/0 | device id: xxxx -------------------------- Hardware | manufacturer: u-blox | model: SARA-U201 | revision: 23.60 | supported: gsm-umts | current: gsm-umts | equipment id: 358887095191472 -------------------------- System | device: /sys/devices/platform/scb/fd500000.pcie/pci0000:00/0000:00:00.0/0000:01:00.0/usb1/1-1/1-1.4 | drivers: cdc_acm | plugin: u-blox | primary port: ttyACM0 | ports: ttyACM3 (unknown), ttyACM4 (unknown), ttyACM5 (unknown), | ttyACM6 (unknown), ttyACM0 (at), ttyACM1 (at), ttyACM2 (at) -------------------------- Status | unlock retries: sim-pin (3), sim-pin2 (3), sim-puk (10), sim-puk2 (10) | state: connected | power state: on | access tech: umts | signal quality: 20% (recent) -------------------------- Modes | supported: allowed: 2g; preferred: none | allowed: 2g, 3g; preferred: none | allowed: 2g, 3g; preferred: 2g | allowed: 2g, 3g; preferred: 3g | allowed: 3g; preferred: none | current: allowed: 2g, 3g; preferred: 3g -------------------------- Bands | supported: egsm, dcs, pcs, g850, utran-1, utran-3, utran-4, utran-6, | utran-5, utran-8, utran-2, utran-7, utran-11 | current: egsm, pcs, g850, utran-1, utran-6, utran-5, utran-8, utran-2 -------------------------- IP | supported: ipv4, ipv6, ipv4v6 -------------------------- 3GPP | imei: xxxx | operator id: xxxx | operator name: vodafone NL | registration: roaming -------------------------- SIM | dbus path: /org/freedesktop/ModemManager1/SIM/0 -------------------------- Bearer | dbus path: /org/freedesktop/ModemManager1/Bearer/0 But randomly it disconnects and starts flooding the log, not willing to connect again. The reason it cannot reconnect again is: NetworkManager[387]: [1576251985.8713] modem-broadband[ttyACM0]: failed to connect modem: Could not open serial device ttyACM0: it has been forced close Of which I think the issue is addressed here: https://lists.freedesktop.org/archives/modemmanager-devel/2018-August/006593.html Below is the output of a part of journalctl --boot -1 Dec 13 16:46:23 447452017112 run.sh[362]: wal Dec 13 16:46:24 447452017112 run.sh[362]: wal Dec 13 16:46:24 447452017112 pppd[2394]: LCP terminated by peer Dec 13 16:46:24 447452017112 pppd[2394]: nm-ppp-plugin: (nm_phasechange): status 8 / phase 'network' Dec 13 16:46:24 447452017112 NetworkManager[387]: LCP terminated by peer Dec 13 16:46:24 447452017112 NetworkManager[387]: Connect time 6.1 minutes. Dec 13 16:46:24 447452017112 NetworkManager[387]: Sent 7957670 bytes, received 2555477 bytes. Dec 13 16:46:24 447452017112 pppd[2394]: Connect time 6.1 minutes. Dec 13 16:46:24 447452017112 NetworkManager[387]: [1576251984.6522] device (ppp0): state change: disconnected -> unmanaged (reason 'connection-assumed', sys-iface-state: 'external') Dec 13 16:46:24 447452017112 pppd[2394]: Sent 7957670 bytes, received 2555477 bytes. Dec 13 16:46:24 447452017112 pppd[2394]: nm-ppp-plugin: (nm_phasechange): status 5 / phase 'establish' Dec 13 16:46:24 447452017112 run.sh[362]: wal Dec 13 16:46:25 447452017112 run.sh[362]: wal Dec 13 16:46:25 447452017112 pppd[2394]: Modem hangup Dec 13 16:46:25 447452017112 NetworkManager[387]: Modem hangup Dec 13 16:46:25 447452017112 NetworkManager[387]: Connection terminated. Dec 13 16:46:25 447452017112 pppd[2394]: nm-ppp-plugin: (nm_phasechange): status 11 / phase 'disconnect' Dec 13 16:46:25 447452017112 pppd[2394]: Connection terminated. Dec 13 16:46:25 447452017112 NetworkManager[387]: [1576251985.7740] device (ttyACM0): state change: activated -> failed (reason 'ip-config-unavailable', sys-iface-state: 'managed') Dec 13 16:46:25 447452017112 ModemManager[395]: network request to deactivate context (type IP, address 172.33.70.239, cid 5) Dec 13 16:46:25 447452017112 ModemManager[395]: Bearer /org/freedesktop/ModemManager1/Bearer/0: explicitly disconnected Dec 13 16:46:25 447452017112 ModemManager[395]: (ttyACM0): could not re-acquire serial port lock: (5) Input/output error Dec 13 16:46:25 447452017112 ModemManager[395]: Modem /org/freedesktop/ModemManager1/Modem/0: state changed (connected -> registered) Dec 13 16:46:25 447452017112 NetworkManager[387]: [1576251985.7977] device (ttyACM0): Activation: failed for connection 'mymodem' Dec 13 16:46:25 447452017112 dbus-daemon[369]: [system] Activating via systemd: service name='org.freedesktop.nm_dispatcher' unit='dbus-org.freedesktop.nm-dispatcher.service' requested by ':1.7' (uid=0 Dec 13 16:46:25 447452017112 NetworkManager[387]: [1576251985.8072] modem["ttyACM0"]: modem state changed, 'connected' --> 'registered' (reason: user-requested) Dec 13 16:46:25 447452017112 NetworkManager[387]: [1576251985.8080] device (ttyACM0): state change: failed -> disconnected (reason 'none', sys-iface-state: 'managed') Dec 13 16:46:25 447452017112 systemd[1]: Starting Network Manager Script Dispatcher Service... Dec 13 16:46:25 447452017112 NetworkManager[387]: [1576251985.8133] policy: auto-activating connection 'mymodem' (209621ae-13a5-49de-9009-23cb00fc52d7) Dec 13 16:46:25 447452017112 NetworkManager[387]: [1576251985.8172] device (ttyACM0): Activation: starting connection 'mymodem' (209621ae-13a5-49de-9009-23cb00fc52d7) Dec 13 16:46:25 447452017112 NetworkManager[387]: [1576251985.8178] device (ttyACM0): state change: disconnected -> prepare (reason 'none', sys-iface-state: 'managed') Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect started... Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect state (4/8): Wait to get fully enabled Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect state (5/8): Register Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect state (6/8): Bearer Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect started... Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect state (4/8): Wait to get fully enabled Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect state (5/8): Register Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect state (6/8): Bearer Dec 13 16:46:25 447452017112 dbus-daemon[369]: [system] Successfully activated service 'org.freedesktop.nm_dispatcher' Dec 13 16:46:25 447452017112 systemd[1]: Started Network Manager Script Dispatcher Service. Dec 13 16:46:25 447452017112 nm-dispatcher[6134]: req:1 'down' [ppp0]: new request (1 scripts) Dec 13 16:46:25 447452017112 nm-dispatcher[6134]: req:1 'down' [ppp0]: start running ordered scripts... Dec 13 16:46:25 447452017112 nm-dispatcher[6134]: req:2 'connectivity-change': new request (1 scripts) Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect started... Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect state (4/8): Wait to get fully enabled Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect state (5/8): Register Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect state (6/8): Bearer Dec 13 16:46:25 447452017112 NetworkManager[387]: [1576251985.8409] modem-broadband[ttyACM0]: failed to connect modem: Could not open serial device ttyACM0: it has been forced close Dec 13 16:46:25 447452017112 NetworkManager[387]: [1576251985.8409] device (ttyACM0): state change: prepare -> failed (reason 'unknown', sys-iface-state: 'managed') Dec 13 16:46:25 447452017112 NetworkManager[387]: [1576251985.8430] device (ttyACM0): Activation: failed for connection 'mymodem' Dec 13 16:46:25 447452017112 NetworkManager[387]: [1576251985.8436] device (ttyACM0): state change: failed -> disconnected (reason 'none', sys-iface-state: 'managed') Dec 13 16:46:25 447452017112 NetworkManager[387]: [1576251985.8480] policy: auto-activating connection 'mymodem' (209621ae-13a5-49de-9009-23cb00fc52d7) Dec 13 16:46:25 447452017112 NetworkManager[387]: [1576251985.8515] device (ttyACM0): Activation: starting connection 'mymodem' (209621ae-13a5-49de-9009-23cb00fc52d7) Dec 13 16:46:25 447452017112 NetworkManager[387]: [1576251985.8520] device (ttyACM0): state change: disconnected -> prepare (reason 'none', sys-iface-state: 'managed') Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect started... Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect state (4/8): Wait to get fully enabled Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect state (5/8): Register Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect state (6/8): Bearer Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect started... Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect state (4/8): Wait to get fully enabled Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect state (5/8): Register Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect state (6/8): Bearer Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect started... Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect state (4/8): Wait to get fully enabled Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect state (5/8): Register Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect state (6/8): Bearer Dec 13 16:46:25 447452017112 NetworkManager[387]: [1576251985.8713] modem-broadband[ttyACM0]: failed to connect modem: Could not open serial device ttyACM0: it has been forced close Dec 13 16:46:25 447452017112 NetworkManager[387]: [1576251985.8714] device (ttyACM0): state change: prepare -> failed (reason 'unknown', sys-iface-state: 'managed') Dec 13 16:46:25 447452017112 NetworkManager[387]: [1576251985.8732] device (ttyACM0): Activation: failed for connection 'mymodem' Dec 13 16:46:25 447452017112 NetworkManager[387]: [1576251985.8739] device (ttyACM0): state change: failed -> disconnected (reason 'none', sys-iface-state: 'managed') Dec 13 16:46:25 447452017112 NetworkManager[387]: [1576251985.8762] policy: auto-activating connection 'mymodem' (209621ae-13a5-49de-9009-23cb00fc52d7) Dec 13 16:46:25 447452017112 NetworkManager[387]: [1576251985.8797] device (ttyACM0): Activation: starting connection 'mymodem' (209621ae-13a5-49de-9009-23cb00fc52d7) Dec 13 16:46:25 447452017112 NetworkManager[387]: [1576251985.8805] device (ttyACM0): state change: disconnected -> prepare (reason 'none', sys-iface-state: 'managed') Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect started... Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect state (4/8): Wait to get fully enabled Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect state (5/8): Register Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect state (6/8): Bearer Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect started... Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect state (4/8): Wait to get fully enabled Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect state (5/8): Register Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect state (6/8): Bearer Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect started... Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect state (4/8): Wait to get fully enabled Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect state (5/8): Register Dec 13 16:46:25 447452017112 ModemManager[395]: Simple connect state (6/8): Bearer Dec 13 16:46:25 447452017112 NetworkManager[387]: [1576251985.8984] modem-broadband[ttyACM0]: failed to connect modem: Could not open serial device ttyACM0: it has been forced close