Ben Stienstra

Serial console over Bluetooth

Notes

The rfcomm process has higher CPU usage when connected.
The rfcomm utility is deprecated since Bluez 5.44. No alternative found yet, maybe look into PAN.

Configure

Server

Stop ModemManager from interefering:

systemctl stop ModemManager
systemctl disable MomdemManager

Modify /etc/bluetooth/main.conf:
```
[Policy]
AutoEnable=true
```

Start and enable bluetooth service:

systemctl enable bluetooth
systemctl start bluetooth

Create systemd service /etc/systemd/system/rfcomm.service

[Unit]
Description=RFCOMM service
After=bluetooth.service
Requires=bluetooth.service

[Service]
ExecStart=/usr/bin/rfcomm watch hci0 1 setsid /sbin/agetty --8bits --noclear -L rfcomm0 115200 linux

[Install]
WantedBy=multi-user.target

Enable and start the rfcomm service:

systemctl enable rfcomm
systemctl start rfcomm

Client

Stop ModemManager from interefering:

systemctl stop ModemManager
systemctl disable MomdemManager

Add user to dialout group.

Pairing and connecting

On the server side:

bluetoothctl
  discoverable on
  pairable on

On the client side:

bluetoothctl
  scan on
  -wait to discover server-
  scan off
  pair <mac>

On the server:

bluetoothctl
  discoverable off
  pairable off
  trust <BT-MAC of client>

Connect to the serial console over bluetooth:

# There should be a rfcomm0 device
crw-rw----. 1 root dialout 216, 0 11 jun 08:14 /dev/rfcomm0

# If device is nonexistent, create one
sudo rfcomm connect /dev/rfcomm0 <BT server-MAC-address> 1 &
Connected /dev/rfcomm0 to <MAC> on channel 1
Press CTRL-C for hangup

# Connect to the serial console:
screen /dev/rfcomm0 115200

Troubleshooting

After resizing your terminal, run: resize.
Check bluetooth is not disabled:
```
rfkill list
```

Ben Stienstra

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