sharing internet from android to linux/windows is available by default in most of the android phones, but the reverse is generally unavailable and sometimes tedious too.

Requirements:

1. linux distro

2. rooted android phone (you can use framaroot for one click root or follow a rigorous method available throughout the web, however this is beyond the scope of this tutoria)

3.reverse tethering tool ("reverse tether" recommended, but it's not a free app)

4. your android phone must have the option "usb tethering" available.

Time to go for the main event:

in your android phone:

1. connect your phone to the linux running pc with usb cable.

2. now enable "usb tethering". (for me this option was in the system settings->more->tethering & portable hotspot->usb tethering (android version 4.2.2))

in your linux pc:

1. now the network manager in linux will configure your new network device and a new network connection will appear in the network settings.

2. go to network settings/network connectons.

3. then select the wired connection that has been newly appeared (for your android phone) and click "options" in the right bottom corner of the window(network settings)

4. then go to the "ipv4 settings" tab and from the "method" drop down list select "shared to other computers". (it remains automatic DHCP by default)

remember, this changes are not for the connection that you are sharing i.e the modem or whatever it is.

now in your android phone:

open reverse tethering tool and start thethering.

it will configure everything for you. you won't need to do anything more.

your phone will be connected to the internet through your linux pc automatically.