/usr/lib/cups/backend/usb DEBUG: list_devices_libusb DEBUG: usb_find_busses=2 DEBUG: usb_find_devices=2
root@ubuntu1004-test3:~# /usr/lib/cups/backend/snmp network socket://10.0.0.57 "FS-1800+" "FS-1800+" "" ""
root@ubuntu1004-test3:~# /usr/lib/cups/backend/dnssd (gives no results after 5 minutes)
/usr/lib/ cups/backend/ usb
DEBUG: list_devices_libusb
DEBUG: usb_find_busses=2
DEBUG: usb_find_devices=2
root@ubuntu1004 -test3: ~# /usr/lib/ cups/backend/ snmp
network socket://10.0.0.57 "FS-1800+" "FS-1800+" "" ""
root@ubuntu1004 -test3: ~# /usr/lib/ cups/backend/ dnssd
(gives no results after 5 minutes)