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 fails (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.
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)