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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 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

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