Open Source Software

reboot(2)



NAME

   reboot - reboot or enable/disable Ctrl-Alt-Del

SYNOPSIS

   /* 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 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.  The
   LINUX_REBOOT_CMD_RESTART and LINUX_REBOOT_CMD_RESTART2 cmd values cause
   a  SIGHUP  signal  to  be  sent.   The  LINUX_REBOOT_CMD_POWER_OFF  and
   LINUX_REBOOT_CMD_HALT cmd values cause a SIGINT signal to be sent.  For
   the other cmd values, -1 is returned and errno is set to EINVAL.

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 caller must have the CAP_SYS_BOOT inside its user namespace.

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 4.09 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
   https://www.kernel.org/doc/man-pages/.



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