2.9BSD/usr/include/sys/reboot.h

/*
 * Arguments to reboot system call.
 * These are passed to boot program in r4
 * and on to init.
 */
#define	RB_ASKNAME	01
#define	RB_SINGLE	02
#define	RB_NOSYNC	04
#define	RB_HALT		010
#define	RB_DUMP		020
#define	RB_NOFSCK	040
#define	RB_POWRFAIL	0100

/*
 * The name of system to boot on automatic reboots.
 */
#define	RB_DEFNAME	"xp(0,0)unix"