REBOOT

NAME

SYNOPSIS

#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

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 aq%saq" 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 processes, 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

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

SEE ALSO

COLOPHON