---
name: "reboot"
section: "2"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
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

## 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)](/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\_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)](/ipmi/4.md) 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)](/ddb/4.md) 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\_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)](/kenv/1.md) 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)](/init/8.md) program in the newly booted system.

- RB\_KEXEC

  Execute a new kernel loaded via **kexec\_load**(*2*). If no kernel was loaded, reboot as normal.

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)](/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

[kexec\_load(2)](/kexec_load/2.md), [crash(8)](/crash/8.md), [halt(8)](/halt/8.md), [init(8)](/init/8.md), [reboot(8)](/reboot/8.md), [savecore(8)](/savecore/8.md), [reboot(9)](/reboot/9.md)

## HISTORY

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