First we need to get the network adapter’s interfaces name.
Generally, the first wired network adapter interface (Ethernet) will be called eth0, but that is not always the case. Likewise, the wireless network adapter interface is wlan0 by default, but sometimes the interfaces are named differently. That’s why you’ll need to check for yourself by running the following command:
ifconfig
Note all interfaces names down except for the one called “lo”, this one should already be set. We’ll just assume that the wired network adapter interface is eth0 and the wireless network adapter is wlan0.
sudo vim /etc/network/interfaces
Add the following at the bottom of the file:
# wired
auto eth0
iface eth0 inet dhcp
# wireless (to see available networks, run "iwlist scan")
auto wlan0
iface eth0 inet dhcp
wpa-ssid YOUR_ROUTER_SSID_HERE
wpa-psk YOUR_ROUTER_PASSWORD_HERE
The way we set that up is a little clumsy, because the kernet will always expect the ethernet cable to be plugged whenever you’re booting.
In other words, if it’s not plugged, it’s going to wait for a while until it is plugged!
In order to not get stuck for 5 minutes during the boot up, do the following:
sudo vim /etc/dhcp/dhclient.conf
Look for the following line: timeout=300
300 seconds is way too long, just change that to 15 instead, and it’ll hang for 15 seconds at boot instead of 300 seconds if you’re not connected.
Reboot, and once you reboot, connect your device to the internet using an ethernet cable and do the following:
sudo apt-get install wpasupplicant
Then you should be good to go.