NAME

     reboot — reboot system or halt processor

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <unistd.h>
     #include <sys/reboot.h>

     int
     reboot(int howto);

DESCRIPTION

     The reboot() system call reboots the system.  Only the super-user may reboot a machine on
     demand.  However, a reboot is invoked automatically in the event of unrecoverable system
     failures.

     The howto argument is a mask of options; the system call interface allows the following
     options, defined in the include file <sys/reboot.h>, to be passed to the new kernel or the
     new bootstrap and init programs.

     RB_AUTOBOOT    The default, causing the system to reboot in its usual fashion.

     RB_ASKNAME     Normally the system only prompts the user if the loader specified root file
                    system has an error.  This flag forces it to always prompt the user for the
                    root partition.

     RB_DFLTROOT    Use the compiled in root device.  Normally, the system uses the device from
                    which it was booted as the root device if possible.  (The default behavior is
                    dependent on the ability of the bootstrap program to determine the drive from
                    which it was loaded, which is not possible on all systems.)

     RB_DUMP        Dump kernel memory before rebooting; see savecore(8) for more information.

     RB_HALT        The processor is simply halted; no reboot takes place.  This option should be
                    used with caution.

     RB_POWERCYCLE  After halting, the shutdown code will do what it can to turn off the power
                    and then turn the power back on.  This requires hardware support, usually an
                    auxiliary microprocessor that can sequence the power supply.  At present only
                    the ipmi(4) driver implements this feature.

     RB_POWEROFF    After halting, the shutdown code will do what it can to turn off the power.
                    This requires hardware support.

     RB_KDB         Load the symbol table and enable a built-in debugger in the system.  This
                    option will have no useful function if the kernel is not configured for
                    debugging.  Several other options have different meaning if combined with
                    this option, although their use may not be possible via the reboot() system
                    call.  See ddb(4) for more information.

     RB_NOSYNC      Normally, the disks are sync'd (see sync(8)) before the processor is halted
                    or rebooted.  This option may be useful if file system changes have been made
                    manually or if the processor is on fire.

     RB_REROOT      Instead of rebooting, unmount all filesystems except the one containing
                    currently-running executable, and mount root filesystem using the same
                    mechanism which is used during normal boot, based on vfs.root.mountfrom
                    kenv(1) variable.

     RB_RDONLY      Initially mount the root file system read-only.  This is currently the
                    default, and this option has been deprecated.

     RB_SINGLE      Normally, the reboot procedure involves an automatic disk consistency check
                    and then multi-user operations.  RB_SINGLE prevents this, booting the system
                    with a single-user shell on the console.  RB_SINGLE is actually interpreted
                    by the init(8) program in the newly booted system.

     When no options are given (i.e., RB_AUTOBOOT is used), the system is rebooted from file
     “kernel” in the root file system of unit 0 of a disk chosen in a processor specific way.  An
     automatic consistency check of the disks is normally performed (see fsck(8)).

RETURN VALUES

     If successful, this call never returns.  Otherwise, a -1 is returned and an error is
     returned in the global variable errno.

ERRORS

     [EPERM]            The caller is not the super-user.

SEE ALSO

     crash(8), halt(8), init(8), reboot(8), savecore(8)

HISTORY

     The reboot() system call appeared in 4.0BSD.