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



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

SYNOPSIS
       /* 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);

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  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  sys-
	      tem with command '%s'" is printed, and a restart (using the com-
	      mand string given in arg) is performed immediately.  If not pre-
	      ceded 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 ker-
       nel command-line arguments ("reboot=...") to be either  warm  or	 cold,
       and either hard or through the BIOS.

   Behavior inside PID namespaces
       Since  Linux  3.4,  when	 reboot()  is called from a PID namespace (see
       pid_namespaces(7)) other than the initial PID namespace, the effect  of
       the  call  is  to  send	a signal to the namespace "init" process.  The
       LINUX_REBOOT_CMD_RESTART and LINUX_REBOOT_CMD_RESTART2 cmd values cause
       a  SIGHUP  signal  to  be  sent.	  The  LINUX_REBOOT_CMD_POWER_OFF  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.

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 caller must have the CAP_SYS_BOOT inside its user namespace.

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

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

COLOPHON
       This page is part of release 4.10 of the Linux  man-pages  project.   A
       description  of	the project, information about reporting bugs, and the
       latest	 version    of	  this	  page,	   can	   be	  found	    at
       https://www.kernel.org/doc/man-pages/.



Linux				  2016-10-08			     REBOOT(2)