.\" Copyright (c) 1998 Andries Brouwer (aeb@cwi.nl), 24 September 1998

.\"

.\" %%%LICENSE_START(VERBATIM)

.\" Permission is granted to make and distribute verbatim copies of this

.\" manual provided the copyright notice and this permission notice are

.\" preserved on all copies.

.\"

.\" Permission is granted to copy and distribute modified versions of this

.\" manual under the conditions for verbatim copying, provided that the

.\" entire resulting derived work is distributed under the terms of a

.\" permission notice identical to this one.

.\"

.\" Since the Linux kernel and libraries are constantly changing, this

.\" manual page may be incorrect or out-of-date.  The author(s) assume no

.\" responsibility for errors or omissions, or for damages resulting from

.\" the use of the information contained herein.  The author(s) may not

.\" have taken the same level of care in the production of this manual,

.\" which is licensed free of charge, as they might when working

.\" professionally.

.\"

.\" Formatted or processed versions of this manual, if unaccompanied by

.\" the source, must acknowledge the copyright and authors of this work.

.\" %%%LICENSE_END

.\"

.\" Modified, 27 May 2004, Michael Kerrisk <mtk.manpages@gmail.com>

.\"     Added notes on capability requirements

.\"

.TH REBOOT 2 2017-09-15 "Linux" "Linux Programmer's Manual"

.SH NAME

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

.SH SYNOPSIS

/* Since kernel version 2.1.30 there are symbolic names LINUX_REBOOT_*

   for the constants and a fourth argument to the call: */

.PP

.B #include <unistd.h>

.br

.B #include <linux/reboot.h>

.PP

.BI "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: */

.PP

.B #include <unistd.h>

.br

.B #include <sys/reboot.h>

.PP

.BI "int reboot(int " cmd );

.SH DESCRIPTION

The

.BR 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

.BR loadkeys (1)).

.PP

This system call fail (with the error

.BR EINVAL )

unless

.I magic

equals

.B LINUX_REBOOT_MAGIC1

(that is, 0xfee1dead) and

.I magic2

equals

.B LINUX_REBOOT_MAGIC2

(that is, 672274793).

However, since 2.1.17 also

.B LINUX_REBOOT_MAGIC2A

(that is, 85072278)

and since 2.1.97 also

.B LINUX_REBOOT_MAGIC2B

(that is, 369367448)

and since 2.5.71 also

.B LINUX_REBOOT_MAGIC2C

(that is, 537993216)

are permitted as values for

.IR magic2 .

(The hexadecimal values of these constants are meaningful.)

.PP

The

.I cmd

argument can have the following values:

.TP

.B LINUX_REBOOT_CMD_CAD_OFF

.RB ( RB_DISABLE_CAD ,

0).

CAD is disabled.

This means that the CAD keystroke will cause a

.B SIGINT

signal to be

sent to init (process 1), whereupon this process may decide upon a

proper action (maybe: kill all processes, sync, reboot).

.TP

.B LINUX_REBOOT_CMD_CAD_ON

.RB ( RB_ENABLE_CAD ,

0x89abcdef).

CAD is enabled.

This means that the CAD keystroke will immediately cause

the action associated with

.BR LINUX_REBOOT_CMD_RESTART .

.TP

.B LINUX_REBOOT_CMD_HALT

.RB ( 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

.BR sync (2),

data will be lost.

.TP

.BR LINUX_REBOOT_CMD_KEXEC

.RB ( RB_KEXEC ,

0x45584543, since Linux 2.6.13).

Execute a kernel that has been loaded earlier with

.BR kexec_load (2).

This option is available only if the kernel was configured with

.BR CONFIG_KEXEC .

.TP

.B LINUX_REBOOT_CMD_POWER_OFF

.RB ( 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

.BR sync (2),

data will be lost.

.TP

.B LINUX_REBOOT_CMD_RESTART

.RB ( RB_AUTOBOOT ,

0x1234567).

The message "Restarting system." is printed, and a default

restart is performed immediately.

If not preceded by a

.BR sync (2),

data will be lost.

.TP

.B LINUX_REBOOT_CMD_RESTART2

(0xa1b2c3d4; since Linux 2.1.30).

The message "Restarting system with command \(aq%s\(aq" is printed,

and a restart (using the command string given in

.IR arg )

is performed immediately.

If not preceded by a

.BR sync (2),

data will be lost.

.TP

.BR LINUX_REBOOT_CMD_SW_SUSPEND

.RB ( 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

.BR CONFIG_HIBERNATION .

.PP

Only the superuser may call

.BR reboot ().

.PP

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.

.\"

.SS Behavior inside PID namespaces

.\" commit cf3f89214ef6a33fad60856bc5ffd7bb2fc4709b

.\" see also commit 923c7538236564c46ee80c253a416705321f13e3

Since Linux 3.4,

if

.BR reboot ()

is called

from a PID namespace other than the initial PID namespace

with one of the

.I 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

.BR pid_namespaces (7).

.PP

The values that can be supplied in

.I cmd

when calling

.BR reboot ()

in this case are as follows:

.TP

.BR LINUX_REBOOT_CMD_RESTART ", " LINUX_REBOOT_CMD_RESTART2

The "init" process is terminated,

and

.BR wait (2)

in the parent process reports that the child was killed with a

.B SIGHUP

signal.

.TP

.BR LINUX_REBOOT_CMD_POWER_OFF ", " LINUX_REBOOT_CMD_HALT

The "init" process is terminated,

and

.BR wait (2)

in the parent process reports that the child was killed with a

.B SIGINT

signal.

.PP

For the other

.I cmd

values,

.BR reboot ()

returns \-1 and

.I errno

is set to

.BR EINVAL .

.SH RETURN VALUE

For the values of

.I cmd

that stop or restart the system,

a successful call to

.BR reboot ()

does not return.

For the other

.I cmd

values, zero is returned on success.

In all cases, \-1 is returned on failure, and

.I errno

is set appropriately.

.SH ERRORS

.TP

.B EFAULT

Problem with getting user-space data under

.BR LINUX_REBOOT_CMD_RESTART2 .

.TP

.B EINVAL

Bad magic numbers or \fIcmd\fP.

.TP

.B EPERM

The calling process has insufficient privilege to call

.BR reboot ();

the caller must have the

.B CAP_SYS_BOOT

inside its user namespace.

.SH CONFORMING TO

.BR reboot ()

is Linux-specific,

and should not be used in programs intended to be portable.

.SH SEE ALSO

.BR systemctl (1),

.BR systemd (1),

.BR kexec_load (2),

.BR sync (2),

.BR bootparam (7),

.BR capabilities (7),

.BR ctrlaltdel (8),

.BR halt (8),

.BR shutdown (8)

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I 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/.