lˈaɪv jˌuːˌɛsbˈiː ˈoʊ sˈɛᵻz lˈaɪk uːbˈuːntuː lˈɪnʌks ɐplˈaɪ ˈɔːl fˈaɪlsɪstəm ɹˈaɪts tʊ ɐ kˈæspɚ fˈaɪlsɪstəm ˌoʊvɚlˈeɪ kˈæspɚɹˌɑːɹdˈʌbəljˌuː ðˈæt, wˈʌns fˈʊl ɔːɹ ˌaʊɾəv flˈæʃ dɹˈaɪv spˈeɪs, bɪkˌʌmz ʌnjˈuːzəbəl ænd ðɪ ˌoʊˈɛs sˈiːsᵻz tə bˈuːt.
LiveUSB OSes like Ubuntu Linux apply all filesystem writes to a casper filesystem overlay (casper-rw) that, once full or out of flash drive space, becomes unusable and the OS ceases to boot.