I seem to have gotten this working now. Bluetooth seems a bit finicky. I'm recapping my steps in full in case someone else finds it useful (though its pretty much what I tried initially). This is for Android JB (4.2.2) on a Nexus 4 and Arch Linux 3.6.7-1, with bluez 4.101 on Gnome 3.6 (w/ gnome-bluetooth).
(this step may not do anything useful)
Turn Bluetooth on Android off and disconnect your USB/Bluetooth Adapter from your Linux machine (or if you have an in built one, reset it using hcitool devname reset)
Connect/turn on your bluetooth adapter on Linux. Ensure your adapter is visible (can be set in gnome-bluetooth -- you should see a bluetooth system tray icon).
Turn on bluetooth on your Android device. Use Android to pair to the adapter (I was unable to pair the other way around from Linux). A dialog will come up asking you for a key. Put in any PIN you want. Gnome should pop up a notification asking you for a key; put in the same PIN you entered earlier. Your Android device and the key should be paired at this point.
In Linux, open up a terminal and check what bluetooth services are available by typing in
sdptool browse local
If you already have a serial port service, make a note of what channel it is. If you don't, you can add the service:
sdptool add --channel=22 SP
Now listen on this channel using rfcomm:
sudo rfcomm listen /dev/rfcomm0 22
rfcomm will block, listening for a connection with a message like
Waiting for connection on channel 22
Back on Android, I used the BlueTerm application (http://pymasde.es/blueterm/, also available freely on the google play store) though any similar application should work. Open up BlueTerm, go to options > Connect Device: select the paired adapter.
Hopefully, the application was able to connect. You'll see additional verification in the terminal where you blocked listening with a message like:
Waiting for connection on channel 22
Connection from 22:22:22:22:22:22 to /dev/rfcomm0
Press CTRL-C for hangup
Anything you type into the BlueTerm app should be going to /dev/rfcomm0. You can see stuff show up as you type by opening up a new terminal and doing something like:
cat /dev/rfcomm0
Best Answer
Even if the bluetooth service was started, the
/dev/rfcomm0device would not just automatically appear.At minimum, the bluetooth subsystem would need to know the address of the Bluetooth device and the channel on it, so that a particular
/dev/rfcomm*device name can be bound to a particular Bluetooth device+channel combination.You can use
rfcomm bind 0 <bdaddr> [channel]to make the binding for/dev/rfcomm0. If you don't specify the channel number, channel 1 will be used by default. If your version of therfcommstill supports the/etc/bluetooth/rfcomm.conffile and you have the address and channel information for/dev/rfcomm0written to it, then you can omit the address and channel information from the command - but you still need to use the command to make the binding.Newer versions of BlueZ tools no longer seem to document the
/etc/bluetooth/rfcomm.conffile. It might be that you'll have to always use the full form of therfcomm bindcommand to set up your bindings. You might want to add these commands to/etc/rc.localor some custom start-up script, to make them execute automatically at boot time, as the associations won't persist through a reboot.It seems that the last major rebuild of BlueZ internals cost us some of the RFCOMM-related features, like the
/etc/bluetooth/rfcomm.conffile. But at least therfcommcommand is still available and can do the job.