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 and most alternative libc's (including uclibc, dietlibc,
          musl and a few others), 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 values 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 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 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_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 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

       kexec_load(2), sync(2), bootparam(7), capabilities(7), ctrlaltdel(8), halt(8), reboot(8)

COLOPHON

       This page is part of release 4.04 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                                              2015-12-05                                          REBOOT(2)