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)