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 (abbrevi‐
       ated 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  con‐
       stants 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 con‐
              figured 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 possi‐
              ble.  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  system  with  command
              '%s'"  is  printed,  and  a restart (using the command string given in arg) is per‐
              formed immediately.  If not preceded 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  (hiber‐
              nated)  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  archi‐
       tecture,  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.

   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_REBOOT_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 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 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 3.74 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)