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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | SEE ALSO | COLOPHON |
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REBOOT(2) Linux Programmer's Manual REBOOT(2)
reboot - reboot or enable/disable Ctrl-Alt-Del
/* 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);
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
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, 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
EINVAL.
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.
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.
reboot() is Linux-specific, and should not be used in programs
intended to be portable.
systemctl(1), systemd(1), kexec_load(2), sync(2), bootparam(7),
capabilities(7), ctrlaltdel(8), halt(8), shutdown(8)
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)
Pages that refer to this page: systemctl(1), kexec_load(2), syscalls(2), systemd.exec(5), systemd.unit(5), capabilities(7), pid_namespaces(7), systemd-halt.service(8)
Copyright and license for this manual page
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