Hello,
I have Ubuntu 21.04, I plugged a Bluetooth 4.0 Adapter Dongle. The dongle was visible to the system because Ubuntu had an active button for the Bluetooth. I checked the status of the Bluetooth and it seemed to be running:

```
sudo service bluetooth status
● bluetooth.service - Bluetooth service
Loaded: loaded (/lib/systemd/system/bluetooth.service; enabled; vendor pre>
Active: active (running) since Mon 2021-09-27 09:54:30 CEST; 57min ago
Docs: man:bluetoothd(8)
Main PID: 1738 (bluetoothd)
Status: "Running"
Tasks: 1 (limit: 38312)
Memory: 1.8M
CGroup: /system.slice/bluetooth.service
└─1738 /usr/lib/bluetooth/bluetoothd

Sep 27 10:12:11 juggernaut bluetoothd[1738]: src/device.c:search_cb() E8:AB:FA:>
Sep 27 10:14:13 juggernaut bluetoothd[1738]: Pair device timed out for hci0
Sep 27 10:16:36 juggernaut bluetoothd[1738]: Pair device timed out for hci0
Sep 27 10:19:29 juggernaut bluetoothd[1738]: Pair device timed out for hci0
Sep 27 10:19:33 juggernaut bluetoothd[1738]: Failed to set mode: Failed (0x03)
Sep 27 10:19:35 juggernaut bluetoothd[1738]: Failed to set mode: Failed (0x03)
Sep 27 10:43:13 juggernaut bluetoothd[1738]: Pair device timed out for hci0
Sep 27 10:45:25 juggernaut bluetoothd[1738]: Failed to set mode: Failed (0x03)
Sep 27 10:45:35 juggernaut bluetoothd[1738]: Failed to set mode: Failed (0x03)
Sep 27 10:49:00 juggernaut bluetoothd[1738]: Failed to set mode: Failed (0x03)
```

However, even if the device I wanted to pair (an earphone) was visible, it could not be paired.
Since the Dongle was 4.0 and the earphone 5.0, I then bought a Dongle 5.0. Even in this case, there is an active button, `sudo service bluetooth status` gives stuff virtually identical to the one above, but not only I can't pair: no device is found to start with.
It might be that the Dongle I bought does not work with Linux, so I bought another that, on paper, should. In this case, there was NO active button: Ubuntu showed no Bluetooth at all (in the face of compatibility).

The bottom line is: how can I activate the Bluetooth on Ubuntu and how can I fix these errors without buying all the Dongles available on Amazon?

Thank you

I guess you need to check the tool bluetoothctl: https://www.makeuseof.com/manage-blu...-bluetoothctl/

Thanks.
I bought yet another dongle and I got:

```
$ sudo systemctl status bluetooth
[sudo] password for gigiux:
● bluetooth.service - Bluetooth service
Loaded: loaded (/lib/systemd/system/bluetooth.service; enabled; vendor pre>
Active: active (running) since Mon 2021-10-11 10:12:00 CEST; 19min ago
Docs: man:bluetoothd(8)
Main PID: 730 (bluetoothd)
Status: "Running"
Tasks: 1 (limit: 38312)
Memory: 1.9M
CGroup: /system.slice/bluetooth.service
└─730 /usr/lib/bluetooth/bluetoothd

Oct 11 10:11:52 juggernaut systemd[1]: Starting Bluetooth service...
Oct 11 10:11:53 juggernaut bluetoothd[730]: Bluetooth daemon 5.56
Oct 11 10:12:00 juggernaut systemd[1]: Started Bluetooth service.
Oct 11 10:12:00 juggernaut bluetoothd[730]: Starting SDP server
Oct 11 10:12:01 juggernaut bluetoothd[730]: Bluetooth management interface 1.19>

$ sudo systemctl enable bluetooth
Synchronizing state of bluetooth.service with SysV service script with /lib/systemd/systemd-sysv-install.
Executing: /lib/systemd/systemd-sysv-install enable bluetooth
$ sudo systemctl start bluetooth
$ bluetoothctl scan on
No default controller available
```
So I switched to the previous dongle 5 and I got again:
```
$ sudo systemctl status bluetooth
[sudo] password for gigiux:
● bluetooth.service - Bluetooth service
Loaded: loaded (/lib/systemd/system/bluetooth.service; enabled; vendor pre>
Active: active (running) since Mon 2021-10-11 10:12:00 CEST; 25min ago
Docs: man:bluetoothd(8)
Main PID: 730 (bluetoothd)
Status: "Running"
Tasks: 1 (limit: 38312)
Memory: 2.0M
CGroup: /system.slice/bluetooth.service
└─730 /usr/lib/bluetooth/bluetoothd
$ bluetoothctl scan on
Discovery started
[CHG] Controller E8:48:B8:C8:20:00 Discovering: yes

```
but nothing happened. I tried also this post, but nothing.