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REBOOT(2) Linux Programmer's Manual REBOOT(2)
reboot - reboot or enable/disable Ctrl-Alt-Del
/* 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);
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_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).
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_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_KEXEC (since Linux 2.6.13)
Execute a kernel that has been loaded earlier with kexec_load(2). This
option is only available if the kernel was configured with
CONFIG_KEXEC.
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_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_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.
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.
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
appropriately.
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.
reboot() is Linux-specific, and should not be used in programs intended to be
portable.
sync(2), bootparam(7), capabilities(7), ctrlaltdel(8), halt(8), reboot(8)
This page is part of release 3.32 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 2010-10-31 REBOOT(2)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface