reboot

REBOOT(2)                  Linux Programmer's Manual                 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  fail  (with  the  error 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  sys-
              tem with command '%s'" is printed, and a restart (using the com-
              mand string given in arg) is performed immediately.  If not pre-
              ceded 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 ker-
       nel 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, if reboot() is called from a PID namespace other than
       the initial PID namespace with one of the cmd values listed  below,  it
       performs  a  "reboot"  of that namespace: the "init" process of the PID
       namespace is immediately terminated,  with  the  effects  described  in
       pid_namespaces(7).

       The  values  that  can be supplied in cmd when calling reboot() in this
       case are as follows:

       LINUX_REBOOT_CMD_RESTART, LINUX_REBOOT_CMD_RESTART2
              The "init" process is terminated,  and  wait(2)  in  the  parent
              process reports that the child was killed with a SIGHUP signal.

       LINUX_REBOOT_CMD_POWER_OFF, LINUX_REBOOT_CMD_HALT
              The  "init"  process  is  terminated,  and wait(2) in the parent
              process reports that the child was killed with a SIGINT signal.

       For the other cmd values, reboot() returns -1 and errno is set to  EIN-
       VAL.

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
       systemctl(1),  systemd(1),  kexec_load(2), sync(2), bootparam(7), capa-
       bilities(7), ctrlaltdel(8), halt(8), shutdown(8)

COLOPHON
       This page is part of release 4.15 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/.

Linux                             2017-09-15                         REBOOT(2)
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