i use git on ubuntu headless server on virtualbox on my laptop. when i shut down the pc, i don't bother shutting down the virtualbox, i just shutdown the pc. it never was a problem. it was fine since yesterday, when the power is gone. laptop had 2 hours remaining so i used it to the last minute, then i closed my ssh session, then closed the laptop. it properly closed, though power was out. morning, when i opened the laptop again, git was corrupted. why did this happen?