RB_SINGLE
RB_MUTE, RB_PAUSE, RB_SERIAL, RB_SINGLE, RB_VERBOSE
howto |= RB_SINGLE;
howto |= RB_SINGLE;
if (boothowto & RB_SINGLE) {
|RB_SINGLE
boothowto |= RB_SINGLE;
{ "boot_single", RB_SINGLE},