I am using ubuntu 15.10 and android 4.0.4. I googled a lot how to reverse tether from ubuntu to android but couldn't find any reasonable answers. So how can i share my ethernet connection on my ubuntu to android? i know i should create a new wifi hotspot from my pc and set it to "shared to other devices" but the wifi hotspot is NOT visible in my android phone! Also creating a wireless network with setting "infrastructure" to "ap" mode did not work for me. Thank you for your answers!
Checkout hostapd.
This documentation for Ubuntu looks like it'd get you going, but you'll probably have to make a few tweaks, like wlan0 will be eth0. wlan1 would be the wireless adapter that is broadcasting to your phone.
https://help.ubuntu.com/community/WifiDocs/WirelessAccessPoint