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Man page of REBOOT
REBOOT
Section: Linux Programmer's Manual (2)
Updated: 2016-10-08
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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 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 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 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.
- 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 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.
The
LINUX_REBOOT_CMD_RESTART
and
LINUX_REBOOT_CMD_RESTART2
cmd
values cause a
SIGHUP
signal to be sent.
The
LINUX_REBOOT_CMD_POWER_OFF
and
LINUX_REBOOT_CMD_HALT
cmd
values cause a
SIGINT
signal to be sent.
For the other
cmd
values, -1 is returned and
errno
is set to
EINVAL.
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
kexec_load(2),
sync(2),
bootparam(7),
capabilities(7),
ctrlaltdel(8),
halt(8),
reboot(8)
COLOPHON
This page is part of release 4.09 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/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- Behavior inside PID namespaces
-
- RETURN VALUE
-
- ERRORS
-
- CONFORMING TO
-
- SEE ALSO
-
- COLOPHON
-
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