device br0 already exists

Here’s how you solve either of the following errors on Ubuntu (and possibly Debian):

Removing the device specs from /etc/network/interfaces and restarting the network doesn’t actually remove the device if already active. You need to do it manually.

List the active devices:

And then do this to any that you don’t want there, such as br0, eth0, eth1, etc:

This deactivates the device. At this point you’ll need to restart the network layer twice:

And you should be sitting pretty. On some systems, networking is known as network, as in: