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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_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  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
              only available if the kernel was configured with CONFIG_KEXEC.

       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_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 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.

       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 3.35 of the Linux man-pages project.  A  description  of  the
       project,  and information about reporting bugs, can be found at http://man7.org/linux/man-
       pages/.