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reboot — reboot system or halt processor
Standard C Library (libc, -lc)
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
RB_ASKNAME Interpreted by the bootstrap program itself, causing it to
prompt on the console as to what file should be booted.
Normally, the system is booted from the file
“xx(0,0)kernel”, where xx is the default disk name, without
prompting for the file name.
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
RB_DUMP Dump kernel memory before rebooting; see savecore(8) for
RB_HALT the processor is simply halted; no reboot takes place.
This option should be used with caution.
RB_POWEROFF After halting, the shutdown code will do what it can to
turn off the power. This requires hardware support.
RB_INITNAME An option allowing the specification of an init program
(see init(8)) other than /sbin/init to be run when the
system reboots. This switch is not currently available.
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_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
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)).
If successful, this call never returns. Otherwise, a -1 is returned and
an error is returned in the global variable errno.
[EPERM] The caller is not the super-user.
crash(8), halt(8), init(8), reboot(8), savecore(8)
The reboot() system call appeared in 4.0BSD.
The HP300 implementation supports neither RB_DFLTROOT nor RB_KDB.