Manpage of REBOOT

REBOOT

Section: Linux Programmer's Manual (2)
Updated: 2016-10-08
Index
 

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 magicequals LINUX_REBOOT_MAGIC1(that is, 0xfee1dead) and magic2equals 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 cmdargument 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 SIGINTsignal 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 aq%saq" 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_RESTARTand LINUX_REBOOT_CMD_RESTART2cmdvalues cause a SIGHUPsignal to be sent. The LINUX_REBOOT_CMD_POWER_OFFand LINUX_REBOOT_CMD_HALTcmdvalues cause a SIGINTsignal to be sent. For the other cmdvalues, -1 is returned and errnois set to EINVAL.  

RETURN VALUE

For the values of cmdthat stop or restart the system, a successful call to reboot() does not return. For the other cmdvalues, zero is returned on success. In all cases, -1 is returned on failure, and errnois 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_BOOTinside 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)


 

Index

NAME
SYNOPSIS
DESCRIPTION
Behavior inside PID namespaces
RETURN VALUE
ERRORS
CONFORMING TO
SEE ALSO

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