If you want to play with turning on or off with the little back, home, menu buttons on your Android Lollipop device (Note: You need to give root access to do this), then below steps will be useful for you.
- Connect your device via adb shell.
In the adb shell terminal give the following command to enable/disable these navigation keys.
//To turn ON soft keys $ setprop qemu.hw.mainkeys 0 //To turn OFF soft keys $ setprop qemu.hw.mainkeys 1
Then stop and start the android to make these changes visible.
$ stop $ start
If you want to make these changes permanent , then add the setprop line (setprop qemu.hw.mainkeys) in your “init.rc” script in your device folder.