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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_RE-
       BOOT_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 fol-
       lowing 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.
       LINUX_REBOOT_CMD_RESTART	 and  LINUX_REBOOT_CMD_RESTART2	cause a	SIGHUP
       signal  to   be	 sent.	  LINUX_REBOOT_CMD_POWER_OFF   and   LINUX_RE-
       BOOT_CMD_HALT cause a SIGINT signal to be sent.

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 er-
       rno is set appropriately.

ERRORS
       EFAULT Problem	with   getting	 user-space   data   under   LINUX_RE-
	      BOOT_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), re-
       boot(8)

COLOPHON
       This page is part of release 3.74 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
       http://www.kernel.org/doc/man-pages/.

Linux				  2014-09-21			     REBOOT(2)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | SEE ALSO | COLOPHON

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