Section 128. Subject to other provisions of law, parole permits, in this chapter also referred to as permits to be at liberty, may be granted by the parole board to prisoners in state and county correctional institutions serving sentences or total aggregate sentences of sixty days or more, or serving sentences suspended in part pursuant to sections one or one A of chapter two hundred and seventy-nine, or a special sentence of imprisonment imposed pursuant to section six A of chapter two hundred and seventy-nine, having a committed portion of sixty days or more.