bluetoothctl - What is a bluetooth agent?

I am using the bluetoothctl utility to set up Bluetooth connections between computers and Raspberry Pis.

In bluetoothctl, I can see there is something called an "agent", and by looking at most of tutorials, this "agent" has to be set "on" to create connections. I am trying to understand what is a bluetooth agent.

1) What is a bluetooth agent ?

2) What is the "default-agent" command in bluetoothctl for ? Can it be the same for all connections ?

3) What is the impact of not using an agent when setting up a connection ?

4) By looking at man bluetoothctl, it is said that agents can be set a capability. What is an agent capability ? What values could be put there ?

5) Do agents only exist with bluetooth ? Are there let's say wifi agents too ?

I am fairly new to the world of Bluetooth, and the documentation for bluetoothctl is quite limited... Any information would be appreciated.

1 Answer

The Bluetooth agent is what manages the Bluetooth 'pairing code'. It can either respond to a 'pairing code' coming in, or can send one out.

The default-agent should work for you. You say you're new to Bluetooth, so I suggest you go with the default for now.

Not using an agent will mean the 2 devices cannot negotiate the 'pairing code'.

An example might help, so here's an example of what worked for me on my Raspberry Pi 3 called Shep:

pi@shep:~/bluetooth $ bluetoothctl
[NEW] Controller B8:27:EB:B0:BC:22 shep [default]
[NEW] Device 18:9E:FC:94:8C:33 iPhone4
[bluetooth]# agent on
Agent registered
[bluetooth]# default-agent
Default agent request successful
[CHG] Device 18:9E:FC:94:8C:33 Connected: yes
[CHG] Device 18:9E:FC:94:8C:33 Connected: no

Here I asked the iPhone to pair with Shep, and iPhone sent 680044.

[CHG] Device 18:9E:FC:94:8C:33 Connected: yes
Request confirmation
[agent] Confirm passkey 680044 (yes/no): yes

Or see the following if you want to set the pass key in advance:

Setup bluetooth-agent to pass the expected pairing code

$ bluetooth-agent 0000 &

Obviously the '0000' could be any number.

These agents and 'pairing codes' are specific to Bluetooth rather than Wi-Fi.