Linux Programmer's Manual --- reboot

REBOOT(2) Linux Programmer's Manual REBOOT(2)

NAME

reboot - reboot or enable/disable Ctrl-Alt-Del

SYNOPSIS

/* For libc4 and libc5 the library call and the system call
are identical, and since kernel version 2.1.30 there are
symbolic names LINUX_REBOOT_* for the constants and a
fourth argument to the call: */

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

int reboot(int magic, int magic2, int cmd, void *arg);

/* Under glibc some of the constants involved have gotten
symbolic names RB_*, and the library call is a 1-argument
wrapper around the 3-argument system call: */

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

int reboot(int cmd);

DESCRIPTION

The reboot() call reboots the system, or enables/disables the reboot keystroke (abbreviated CAD, since the default
is Ctrl-Alt-Delete; it can be changed using loadkeys(1)).

This system call will fail (with EINVAL) unless magic equals LINUX_REBOOT_MAGIC1 (that is, 0xfee1dead) and magic2
equals LINUX_REBOOT_MAGIC2 (that is, 672274793). However, since 2.1.17 also LINUX_REBOOT_MAGIC2A (that is,
85072278) and since 2.1.97 also LINUX_REBOOT_MAGIC2B (that is, 369367448) and since 2.5.71 also
LINUX_REBOOT_MAGIC2C (that is, 537993216) are permitted as value for magic2. (The hexadecimal values of these
constants are meaningful.) The cmd argument can have the following values:

LINUX_REBOOT_CMD_RESTART
(RB_AUTOBOOT, 0x1234567). The message "Restarting system." is printed, and a default restart is performed
immediately. If not preceded by a sync(2), data will be lost.

LINUX_REBOOT_CMD_HALT
(RB_HALT_SYSTEM, 0xcdef0123; since 1.1.76). The message "System halted." is printed, and the system is
halted. Control is given to the ROM monitor, if there is one. If not preceded by a sync(2), data will be
lost.

LINUX_REBOOT_CMD_POWER_OFF
(0x4321fedc; since 2.1.30). The message "Power down." is printed, the system is stopped, and all power is
removed from the system, if possible. If not preceded by a sync(2), data will be lost.

LINUX_REBOOT_CMD_RESTART2
(0xa1b2c3d4; since 2.1.30). The message "Restarting system with command '%s'" is printed, and a restart
(using the command string given in arg) is performed immediately. If not preceded by a sync(2), data will
be lost.

LINUX_REBOOT_CMD_CAD_ON
(RB_ENABLE_CAD, 0x89abcdef). CAD is enabled. This means that the CAD keystroke will immediately cause the
action associated with LINUX_REBOOT_CMD_RESTART.

LINUX_REBOOT_CMD_CAD_OFF
(RB_DISABLE_CAD, 0). CAD is disabled. This means that the CAD keystroke will cause a SIGINT signal to be
sent to init (process 1), whereupon this process may decide upon a proper action (maybe: kill all pro‐
cesses, sync, reboot).

Only the superuser may call reboot().

The precise effect of the above actions depends on the architecture. For the i386 architecture, the additional
argument does not do anything at present (2.1.122), but the type of reboot can be determined by kernel command-
line arguments ("reboot=...") to be either warm or cold, and either hard or through the BIOS.

RETURN VALUE

For the values of cmd that stop or restart the system, a successful call to reboot() does not return. For the
other cmd values, zero is returned on success. In all cases, -1 is returned on failure, and errno is set appro‐
priately.

ERRORS

EFAULT Problem with getting userspace data under LINUX_REBOOT_CMD_RESTART2.

EINVAL Bad magic numbers or cmd.

EPERM The calling process has insufficient privilege to call reboot(); the CAP_SYS_BOOT capability is required.

CONFORMING TO

reboot() is Linux-specific, and should not be used in programs intended to be portable.

SEE ALSO

sync(2), bootparam(7), capabilities(7), ctrlaltdel(8), halt(8), reboot(8)

COLOPHON

This page is part of release 3.27 of the Linux man-pages project. A description of the project, and information
about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.

Linux 2008-02-11 REBOOT(2)