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REBOOT(2) System Calls Manual REBOOT(2)

reboot
reboot system or halt processor

#include <unistd.h>
#include <sys/reboot.h>
int
reboot(int howto);

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

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.
September 10, 2015 OpenBSD-6.0