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_RESTART
              (RB_AUTOBOOT, 0x1234567).  The message "Restarting system." is printed, and a default restart is performed immedi-
              ately.  If not preceded by a sync(2), data will be lost.

       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_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_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.

       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_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).

       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.

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 userspace 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 3.25 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                                                      2008-02-11                                                  REBOOT(2)