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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 (abbrevi‐
ated 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 values for magic2. (The hexadecimal values of these con‐
stants 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 Linux 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
(RB_KEXEC, 0x45584543, since Linux 2.6.13). Execute a kernel that has been loaded
earlier with kexec_load(2). This option is available only if the kernel was con‐
figured with CONFIG_KEXEC.
LINUX_REBOOT_CMD_POWER_OFF
(RB_POWER_OFF, 0x4321fedc; since Linux 2.1.30). The message "Power down." is
printed, the system is stopped, and all power is removed from the system, if possi‐
ble. 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 Linux 2.1.30). The message "Restarting system with command
'%s'" is printed, and a restart (using the command string given in arg) is per‐
formed immediately. If not preceded by a sync(2), data will be lost.
LINUX_REBOOT_CMD_SW_SUSPEND
(RB_SW_SUSPEND, 0xd000fce1; since Linux 2.5.18). The system is suspended (hiber‐
nated) to disk. This option is available only if the kernel was configured with
CONFIG_HIBERNATION.
Only the superuser may call reboot().
The precise effect of the above actions depends on the architecture. For the i386 archi‐
tecture, 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.
Behavior inside PID namespaces
Since Linux 3.4, when reboot() is called from a PID namespace (see pid_namespaces(7))
other than the initial PID namespace, the effect of the call is to send a signal to the
namespace "init" process. LINUX_REBOOT_CMD_RESTART and LINUX_REBOOT_CMD_RESTART2 cause a
SIGHUP signal to be sent. LINUX_REBOOT_CMD_POWER_OFF and LINUX_REBOOT_CMD_HALT cause a
SIGINT signal to be sent.
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 appropriately.
ERRORS
EFAULT Problem with getting user-space 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 3.74 of the Linux man-pages project. A description of the
project, information about reporting bugs, and the latest version of this page, can be
found at http://www.kernel.org/doc/man-pages/.
Linux 2014-09-21 REBOOT(2)
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