NAME

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

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       /* Since Linux 2.1.30 there are symbolic names LINUX_REBOOT_*
          for the constants and a fourth argument to the call: */

       #include <linux/reboot.h>  /* Definition of LINUX_REBOOT_* constants */
       #include <sys/syscall.h>   /* Definition of SYS_* constants */
       #include <unistd.h>

       int syscall(SYS_reboot, int magic, int magic2, int op, 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 <sys/reboot.h>    /* Definition of RB_* constants */
       #include <unistd.h>

       int reboot(int op);

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  fails  (with the error EINVAL) unless magic equals LINUX_REBOOT_MAGIC1
       (that is,  0xfee1dead)  and  magic2  equals  LINUX_REBOOT_MAGIC2  (that  is,  0x28121969).
       However,  since  Linux  2.1.17  also  LINUX_REBOOT_MAGIC2A (that is, 0x05121996) and since
       Linux 2.1.97 also LINUX_REBOOT_MAGIC2B (that is, 0x16041998) and since Linux  2.5.71  also
       LINUX_REBOOT_MAGIC2C  (that  is,  0x20112000)  are  permitted  as values for magic2.  (The
       hexadecimal values of these constants are meaningful.)

       The op 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, if reboot() is called from a PID namespace other  than  the  initial  PID
       namespace  with  one  of  the  op  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 op 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 op values, reboot() returns -1 and errno is set to EINVAL.

RETURN VALUE

       For  the  values of op that stop or restart the system, a successful call to reboot() does
       not return.  For the other op values, zero is returned on success.  In all  cases,  -1  is
       returned on failure, and errno is set to indicate the error.

ERRORS

       EFAULT Problem with getting user-space data under LINUX_REBOOT_CMD_RESTART2.

       EINVAL Bad magic numbers or op.

       EPERM  The  calling  process  has insufficient privilege to call reboot(); the caller must
              have the CAP_SYS_BOOT inside its user namespace.

STANDARDS

       Linux.

SEE ALSO

       systemctl(1),   systemd(1),   kexec_load(2),   sync(2),   bootparam(7),   capabilities(7),
       ctrlaltdel(8), halt(8), shutdown(8)