I am using the bluez package for my bluetooth usb dongle on ubuntu server. I want to be able to initiate bluetooth connection from the dongle to a device, however a device itself shall not be able to find by bluetooth dongle or initiate a connection / pairing. In the /etc/bluetooth files I could only find options to set the time my bluetooth dongle will be visible to 1 second, but I want to disable the visibility at all, like it can be done in any mobile phone! Any hint on this? Thanks :-)
Your Bluetooth dongle is invisible by default, as long as you don't change that in some place (like the Bluetooth panel).
However, any paired device will be able to connect to your dongle even if its invisible: That's due to the fact paired devices know your dongle's MAC address which they page directly.
If you don't want your dongle to respond to neither discovery nor connection attempts, run this command:
sudo hciconfig hci0 noscan
which basically puts your dongle in a "send-only" mode. Mind this is not persistent upon boots, so you'll have to add it to some startup script / menu if you want to apply it by default.