---
name: "reboot"
section: "2"
platform: "macos"
package: "xnu"
version: "12377.121.6"
release: "macOS 26.5"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/reboot/2"
---

# reboot(2)

reboot system or halt processor

## NAME

**reboot** – reboot system or halt processor

## SYNOPSIS

**#include \<unistd.h\>**

**#include \<sys/reboot.h\>**

*int*\

**reboot**(*int howto*);

## DESCRIPTION

**reboot**() reboots the system.  Only the super-user may reboot a machine on demand. However, a reboot may be invoked automatically in the event of unrecoverable system failures.  Programs other than [reboot(8)](/reboot/8.md) should not call **reboot**(). Shutdown(8) or a higher-level API will shut the system down cleanly.

*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.

- RB\_AUTOBOOT

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

- 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)bsd”, 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 systems.)

- RB\_DUMP

  Dump kernel memory before rebooting; see [savecore(8)](/savecore/8.md) for more information.

- RB\_HALT

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

- RB\_INITNAME

  An option allowing the specification of an init program (see launchd(8)) other than */sbin/launchd* 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**() call. See kadb(4) for more information.

- RB\_NOSYNC

  Normally, the disks are sync'd (see [sync(8)](/sync/8.md)) 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 launchd(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)](/fsck/8.md)).

## 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

[shutdown(8)](/shutdown/8.md), [halt(8)](/halt/8.md), launchd(8), [reboot(8)](/reboot/8.md)

## BUGS

The HP300 implementation supports neither RB\_DFLTROOT nor RB\_KDB.

## HISTORY

The **reboot**() function call appeared in 4.0BSD.