reboot - reboot or enable/disable Ctrl-Alt-Del
Standard C library (
libc,
-lc)
/* Since Linux 2.1.30 there are symbolic names LINUX_REBOOT_*
for the constants and a fourth argument to the call: */
#include <linux/reboot.h> /* Definition of LINUX_REBOOT_* constants */
#include <sys/syscall.h> /* Definition of SYS_* constants */
#include <unistd.h>
int syscall(SYS_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 <sys/reboot.h> /* Definition of RB_* constants */
#include <unistd.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 fails (with the error
EINVAL) unless
magic equals
LINUX_REBOOT_MAGIC1 (that is, 0xfee1dead) and
magic2 equals
LINUX_REBOOT_MAGIC2 (that is, 0x28121969). However, since Linux 2.1.17
also
LINUX_REBOOT_MAGIC2A (that is, 0x05121996) and since Linux 2.1.97
also
LINUX_REBOOT_MAGIC2B (that is, 0x16041998) and since Linux 2.5.71
also
LINUX_REBOOT_MAGIC2C (that is, 0x20112000) 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.
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 to indicate the error.
- 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)