So for this you need to use

sudo crontab -e

@reboot /



Replace [CONFIGNAME] with config name from wpa_supplicant, and add more if needed. \n = new line


sudo sh -c 'echo "allow-hotplug wlan0\niface wlan0 inet manual\nwpa-roam /etc/wpa_supplicant/wpa_supplicant.conf\niface [CONFIGNAME] inet dhcp" >> /etc/network/interfaces' && sudo wpa_supplicant -d -i wlan0 -c /etc/wpa_supplicant/wpa_supplicant.conf -D wext

Also make sure to:

sudo apt-get purge network-manager


[Not needed for eth0 and doesnt work with wpa_supplicant.conf]