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REBOOT(2) System Calls Manual REBOOT(2)

rebootreboot system or halt processor

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

reboot(int howto);

() reboots the system. Only the superuser may reboot a machine on demand. However, a reboot is invoked automatically in the event of unrecoverable system failures.

howto 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.

The default, causing the system to reboot in its usual fashion.
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)bsd”, where xx is the default disk name, without prompting for the file name.
Dump kernel memory before rebooting; see savecore(8) for more information.
The processor is simply halted; no reboot takes place.
If used in conjunction with RB_HALT, and if the system hardware supports the function, the system will be powered off.
By default, the system will halt if () is called during startup (before the system has finished autoconfiguration), even if RB_HALT is not specified. This is because panic(9)s during startup will probably just repeat on the next boot. Use of this option implies that the user has requested the action specified (for example, using the ddb(4) boot reboot command), so the system will reboot if a halt is not explicitly requested.
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() call. See ddb(4) for more information.
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.
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 /bsd 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)).

Don't update the hardware clock from the system clock, presumably because the system clock is suspect.

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

The caller is not the superuser.

ddb(4), crash(8), halt(8), init(8), reboot(8), savecore(8), boot(9), panic(9)

The reboot() system call finally appeared in 4.0BSD.

Not all platforms support all possible arguments.

April 15, 2017 OpenBSD-6.7