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fm350_portable

Portable Linux helper package for Fibocom FM350-GL / Dell DW5931e-eSIM 5G modem in USB RNDIS + AT mode.

This project provides a repeatable way to use the FM350-GL modem on Linux machines through:

  • NetworkManager
  • USB RNDIS network interface
  • AT command control port
  • automatic modem/interface detection
  • terminal diagnostics similar to a lightweight NetMonster view

Main validated setup:

Q370 / Manjaro KDE
Fibocom FM350-GL / Dell DW5931e-eSIM
USB ID: 0e8d:7127
GTUSBMODE: 41
NetworkManager
RNDIS interface: enp0s20f0u3
AT port: /dev/ttyUSB3

Polish documentation is available in:

README_PL.md

1. Project goal

fm350_portable automates setup and runtime handling for the FM350-GL modem in:

RNDIS + AT mode

The package can:

  • detect the FM350-GL modem by USB ID,
  • detect the AT command port,
  • detect the RNDIS network interface,
  • create a NetworkManager profile named FM350_RNDIS,
  • activate the cellular data context over AT,
  • assign the modem-provided IP address to the RNDIS interface,
  • set the default route through the modem,
  • enforce DNS while the modem connection is active,
  • provide fm350info, a terminal-based FM350 diagnostic tool.

2. Supported modem

Tested modem:

Fibocom FM350-GL / Dell DW5931e-eSIM

Supported USB IDs:

0e8d:7127  GTUSBMODE=41
0e8d:7126  GTUSBMODE=40

Primary tested mode:

GTUSBMODE=41

3. Repository layout

fm350_portable/
├── bootstrap.sh
├── install_fm350.fish
├── uninstall_fm350.fish
├── fm350-detect
├── fm350-connect
├── fm350-disconnect
├── fm350info
├── dispatcher/
│   ├── 90-fm350-rndis
│   └── 95-fm350-dns-guard
├── .gitignore
├── README.md
└── README_PL.md

4. Quick start

Clone the repository:

git clone https://github.com/torpix/fm350_portable.git
cd fm350_portable

Run the bootstrap script:

sh ./bootstrap.sh

The bootstrap script checks dependencies and runs:

sudo fish ./install_fm350.fish --autoconnect yes

Reboot after installation:

sudo reboot

After reboot:

fm350-detect
fm350info
ip route get 1.1.1.1

5. Manual installation

Manjaro / Arch Linux

Install base dependencies:

sudo pacman -S --needed git fish networkmanager ethtool usbutils iproute2

Install atinout if it is not already available. On Arch-based systems it may be available through AUR, for example with yay or pamac.

Then run:

sudo fish ./install_fm350.fish --autoconnect yes
sudo reboot

Kali / Debian

Install dependencies:

sudo apt update
sudo apt install -y git fish network-manager ethtool usbutils iproute2 atinout

Then run:

sudo fish ./install_fm350.fish --autoconnect yes
sudo reboot

6. What the installer does

install_fm350.fish performs the following steps:

  1. Detects the FM350-GL modem.
  2. Detects the AT command port, for example:
/dev/ttyUSB3
  1. Detects the RNDIS network interface, for example:
enp0s20f0u3
  1. Writes the runtime configuration to:
/etc/fm350-rndis.conf

Example configuration:

FM_IF="enp0s20f0u3"
AT_PORT="/dev/ttyUSB3"
APN="internet"
DNS1="1.1.1.1"
DNS2="8.8.8.8"
DNS3="9.9.9.9"
ROUTE_METRIC="100"
AUTOCONNECT="yes"
DISABLE_MODEMMANAGER_FOR_FM350="yes"
  1. Installs helper scripts:
/usr/local/sbin/fm350-detect
/usr/local/sbin/fm350-connect
/usr/local/sbin/fm350-disconnect
/usr/local/bin/fm350info
  1. Installs NetworkManager dispatcher scripts:
/etc/NetworkManager/dispatcher.d/90-fm350-rndis
/etc/NetworkManager/dispatcher.d/95-fm350-dns-guard
  1. Creates or updates the NetworkManager connection:
FM350_RNDIS
  1. Enables autoconnect if requested:
--autoconnect yes

7. ModemManager handling

This package does not globally mask ModemManager by default.

This is intentional. Some laptops may contain an additional internal LTE modem, for example a Dell WWAN module. Globally disabling ModemManager could break that device.

Instead, this package is designed to keep ModemManager away from the FM350-GL by matching the FM350 USB ID.

Global ModemManager masking is available only as an explicit option:

sudo fish ./install_fm350.fish --autoconnect yes --mask-modemmanager

Use this only if you intentionally want to disable ModemManager system-wide.

8. AT port permissions

The AT port usually looks like this:

crw-rw---- root uucp /dev/ttyUSB3

The installer detects the port group and adds the installing user to that group, for example:

uucp

After installation, log out and log back in, or reboot:

sudo reboot

Without a new login session, fm350info may still require sudo.

9. fm350info — lightweight NetMonster-style diagnostics

fm350info prints:

  • operator,
  • LTE/5G registration state,
  • signal data,
  • Cell ID / TAC / PCI / channel data,
  • LTE/NR bands,
  • carrier aggregation information,
  • active APN,
  • modem IP address,
  • Linux routing state,
  • DNS state.

Run:

fm350info

Fallback:

sudo fm350info

Commands used internally include:

AT+COPS?
AT+CEREG?
AT+CGREG?
AT+CSQ
AT+CESQ
AT+GTCCINFO?
AT+GTCAINFO?
AT+GTACT?
AT+CGACT?
AT+CGPADDR=1
AT+CGCONTRDP=1

10. Band code interpretation

Common FM350 band code mapping used by this package:

101  = LTE B1
103  = LTE B3
107  = LTE B7
120  = LTE B20
128  = LTE B28

501  = NR n1
503  = NR n3
5028 = NR n28
5078 = NR n78

Example output:

PCC:5078 ... -109
PCC:101  ... -105
SCC 1:103 ...

Interpretation:

5G NR n78
LTE B1
LTE B3 as secondary carrier

11. Connectivity checks

After installation:

nmcli connection show --active | grep -E 'FM350|LAN'
ip -br addr
ip route get 1.1.1.1
cat /etc/resolv.conf
curl -4 --interface <FM_IF> -I --max-time 20 https://speed.cloudflare.com

Example for the Q370 test machine:

curl -4 --interface enp0s20f0u3 -I --max-time 20 https://speed.cloudflare.com

Expected result:

HTTP/1.1 200 OK

12. Manual connect and disconnect

Connect through NetworkManager:

sudo nmcli connection up FM350_RNDIS

Disconnect:

sudo nmcli connection down FM350_RNDIS

Direct helper scripts:

sudo fm350-connect
sudo fm350-disconnect

13. Uninstall

Run:

sudo fish ./uninstall_fm350.fish

The uninstaller removes:

  • FM350 helper scripts,
  • FM350 dispatcher scripts,
  • optional NetworkManager profile entries.

It does not remove system packages, does not remove ModemManager, and does not modify unrelated LAN profiles.

14. Safety notes

Do not use old scripts that communicate with the modem through patterns such as:

cat /dev/ttyUSBx
printf ... > /dev/ttyUSBx

If the serial port disappears, such code may accidentally create a regular file in /dev, for example:

/dev/ttyUSB3

That can break modem detection.

This project uses:

atinout + timeout + character device checks

Before using an AT port, scripts verify that it is a character device:

[ -c "$AT_PORT" ]

15. Logs

Typical log files:

/tmp/fm350-rndis.log
/tmp/fm350-rndis-dispatcher.log
/tmp/fm350-dns-guard.log
/tmp/fm350info-UID.log

fm350info uses a per-user log file:

/tmp/fm350info-1000.log

Lack of write access to a log file should not block AT command execution.

16. Troubleshooting

AT_PORT=auto

Check USB and serial devices:

lsusb
ls -l /dev/ttyUSB*
sudo fm350-detect

Manual AT port test:

for p in /dev/ttyUSB*; do
  if [ -c "$p" ]; then
    echo "### $p"
    printf 'ATE0\nATI\nAT+GTUSBMODE?\n' | sudo timeout 10s atinout - "$p" -
  fi
done

FM350_RNDIS is active, but there is no internet

Check:

ip -br addr
ip route get 1.1.1.1
cat /etc/resolv.conf
curl -4 --interface <FM_IF> -I --max-time 20 https://speed.cloudflare.com

fm350info requires sudo

Check group membership:

groups
stat -c '%U %G %a %n' /dev/ttyUSB3

If the user is not in the port group, rerun the installer or add the user to the group manually.

After changing groups, log out and log back in or reboot.

Route still points to LAN

Check:

ip route get 1.1.1.1
nmcli connection show --active

Force the modem connection:

sudo nmcli connection up FM350_RNDIS

17. Q370 validation status

Validated on:

Q370 / Manjaro KDE
FM350-GL / Dell DW5931e-eSIM
USB ID: 0e8d:7127
GTUSBMODE: 41
NetworkManager
RNDIS interface: enp0s20f0u3
AT port: /dev/ttyUSB3

Confirmed:

reboot autostart: OK
FM350_RNDIS active: OK
default route through modem: OK
HTTP through modem: OK
fm350info without sudo: OK
per-user fm350info log: OK

18. Planned tests

Pending:

Dell Precision 7510 / Manjaro
Dell 7220 / Kali
different interface names
different AT port numbers
different SIM/operator
antenna and modem placement tests

19. Minimal workflow on a new machine

git clone https://github.com/torpix/fm350_portable.git
cd fm350_portable
sh ./bootstrap.sh
sudo reboot
fm350info
ip route get 1.1.1.1

20. Current status

Q370: PASS
Dell Precision 7510: pending
Dell 7220 / Kali: pending

21. Maintainer

torpix

This is a practical helper package for personal Linux infrastructure and FM350-GL modem testing.

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Portable Linux helper for Fibocom FM350-GL / Dell DW5931e-eSIM 5G modem in USB RNDIS + AT mode

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5gatinoutfibocomfm350-gllinuxmodemnetworkmanagerrndis

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