REBOOT(2) Linux Programmer's Manual REBOOT(2)
NAME
reboot - reboot or enable/disable Ctrl-Alt-Del
SYNOPSIS
/* 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 and most alternative libc's (including uclibc, dietlibc,
musl and a few others), some of the constants involved have gotten
symbolic names RB_*, and the library call is a 1-argument
wrapper around the 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 fail (with the error 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 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 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 configured 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 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 Linux 2.1.30). The message "Restarting sys-
tem with command '%s'" is printed, and a restart (using the com-
mand string given in arg) is performed immediately. If not pre-
ceded 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 (hibernated) 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 architecture, the additional argument does not do anything
at present (2.1.122), but the type of reboot can be determined by ker-
nel 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, if reboot() is called from a PID namespace other than
the initial PID namespace with one of the cmd values listed below, it
performs a "reboot" of that namespace: the "init" process of the PID
namespace is immediately terminated, with the effects described in
pid_namespaces(7).
The values that can be supplied in cmd when calling reboot() in this
case are as follows:
LINUX_REBOOT_CMD_RESTART, LINUX_REBOOT_CMD_RESTART2
The "init" process is terminated, and wait(2) in the parent
process reports that the child was killed with a SIGHUP signal.
LINUX_REBOOT_CMD_POWER_OFF, LINUX_REBOOT_CMD_HALT
The "init" process is terminated, and wait(2) in the parent
process reports that the child was killed with a SIGINT signal.
For the other cmd values, reboot() returns -1 and errno is set to EIN-
VAL.
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 caller must have the CAP_SYS_BOOT inside its user namespace.
CONFORMING TO
reboot() is Linux-specific, and should not be used in programs intended
to be portable.
SEE ALSO
systemctl(1), systemd(1), kexec_load(2), sync(2), bootparam(7), capa-
bilities(7), ctrlaltdel(8), halt(8), shutdown(8)
COLOPHON
This page is part of release 4.15 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
https://www.kernel.org/doc/man-pages/.
Linux 2017-09-15 REBOOT(2)
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