So probably my non-working default wifi settings also has something to do with this, though I found a less extreme solution as described above.

Also the wireless prefixes are the old ones not the ones in Debian. Don't ask me what they are. I don't have wireless enabled.

Yesterday I moved my devuan machine to a new location where there's only wifi access (no direct ethernet connection). After moving I discovered I couldn't connect to wifi. Thankfully, some googling on my mobile device solved the problem. So I'm posting this here in case somebody in a similar situation may find it helpful.

1) First, a few packages are required for WiFi access: wireless-tools and wpasupplicant. Also, you probably need a DHCP client (unless your wifi network allocates static IPs for your machine), so install also isc-dhcp-client. Well, of course, you also need a wireless adapter and the requisite kernel drivers, but that IMO goes without saying.

2) Use iwconfig to find the name of the wireless interface (e.g., 'wlan0'). Add the following stanza to /etc/network/interfaces to create a definition for this interface:

auto wlan0
allow-hotplug wlan0
iface wlan0 inet dhcp
	wpa-conf	/etc/wpa_supplicant/wpa_supplicant.conf

The `wpa-conf` line is the magic sauce for the next step to work, because, as I found out the hard way, Debian/Devuan's default config runs wpa-supplicant without any additional options, so it will ignore the wpa_supplicant.conf file and you won't be able to connect.  You could also use the `wpa-ssid` and `wpa-psk` directives instead of `wpa-conf` if you only have a single network you want to connect to always. But the `wpa-conf` route is needed if you have multiple networks which you can choose from, and you want wpa-supplicant to automatically select the one with the best signal strength.

3) Now create the file /etc/wpa_supplicant/wpa_supplicant.conf with the following contents (replace the ssid and psk with the relevant credentials):

ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
network={
	ssid="MyNetworkSSID"
	scan_ssid=1
	key_mgmt=WPA-PSK
	psk="MySecretPassword"
}

You can add more than one network definition in this file; simply create more network={...} blocks like above and fill in the relevant details.

4) Now running `ifup wlan0` should connect to the wifi network and bring up the interface. The `auto wlan0` line in /etc/network/interfaces will bring it up on reboot; comment out or delete this line if you want to bring it up manually instead.