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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_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  per-
              formed immediately.  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 3.22 of the Linux man-pages project.  A description of the project,  and  informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                             2008-02-11                         REBOOT(2)