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: */
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: */
int reboot(int cmd);
() 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
(that is, 0xfee1dead) and magic2
(that is, 672274793). However, since 2.1.17 also
(that is, 85072278) and since 2.1.97 also
(that is, 369367448) and since 2.5.71 also
(that is, 537993216) are permitted as values for
. (The hexadecimal values of these constants are meaningful.)
argument can have the following values:
- (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).
- (RB_ENABLE_CAD, 0x89abcdef). CAD is enabled. This
means that the CAD keystroke will immediately cause the action associated
- (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.
- (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
- (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.
- (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
- (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.
- (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, when reboot
() is called from a PID namespace (see
) other than the initial PID namespace, the effect of
the call is to send a signal to the namespace "init" process. The
values cause a SIGHUP
signal to be sent. The
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
For the values of cmd
that stop or restart the system, a successful call
() 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.
- Problem with getting user-space data under
- Bad magic numbers or cmd.
- The calling process has insufficient privilege to call
reboot(); the caller must have the CAP_SYS_BOOT inside its
() is Linux-specific, and should not be used in programs intended
to be portable.
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