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Linux 2.6 - man page for reboot (linux section 2)

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

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

       /* 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);

       The  reboot()  call reboots the system, or enables/disables the reboot keystroke (abbrevi-
       ated 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  con-
       stants are meaningful.)	The cmd 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 with LINUX_REBOOT_CMD_RESTART.

	      (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
	      available only if the kernel was configured with CONFIG_KEXEC.

	      (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.

	      (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.

	      (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 immedi-
	      ately.  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 archi-
       tecture, 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.

       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  CAP_SYS_BOOT
	      capability is required.

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

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

       This  page  is  part of release 3.55 of the Linux man-pages project.  A description of the
       project,    and	  information	 about	  reporting    bugs,	can    be    found     at

Linux					    2010-10-31					REBOOT(2)

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