To put linino back to where it was after the last sysupgrade (or when you got it out of the box if you haven't sysupgraded):
Load yunserialterminal
Open serial monitor, set line ending to newline
Push yun reset button (the one by the leds)
Put an "f" in the text box at the top of the serial monitor
Wait for the failsafe prompt, press enter
Run firstboot at the root@none prompt
Wait for AT LEAST 5 minutes.
Press yun reset again