REBOOT(2)						     Linux Programmer's Manual							 REBOOT(2)

NAME

       reboot - reboot or enable/disable Ctrl-Alt-Del

SYNOPSIS

       /* For libc4 and libc5 the library call and the system call
	  are identical, and 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 some of the constants involved have gotten
	  symbolic names RB_*, and the library call is a 1-argument
	  wrapper around the 3-argument 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  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	value  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 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 (since Linux 2.6.13)
	      Execute a kernel that has been loaded earlier with kexec_load(2).  This option is only available if the kernel was  configured  with
	      CONFIG_KEXEC.

       LINUX_REBOOT_CMD_POWER_OFF
	      (0x4321fedc;  since 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 pre-
	      ceded by a sync(2), data will be lost.

       LINUX_REBOOT_CMD_RESTART2
	      (0xa1b2c3d4;  since  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.

       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  any-
       thing  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.

RETURN VALUE

       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.

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 CAP_SYS_BOOT capability is required.

CONFORMING TO

       reboot() is Linux-specific, and should not be used in programs intended to be portable.

SEE ALSO

       sync(2), bootparam(7), capabilities(7), ctrlaltdel(8), halt(8), reboot(8)

COLOPHON

       This  page is part of release 3.44 of the Linux man-pages project.  A description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

Linux								    2010-10-31								 REBOOT(2)