REBOOT(2)                 Linux Programmer's Manual                REBOOT(2)

NAME         top

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

SYNOPSIS         top

       /* Since kernel version 2.1.30 there are symbolic names
          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,
          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         top

       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:

              (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).

              (RB_ENABLE_CAD, 0x89abcdef).  CAD is enabled.  This means that
              the CAD keystroke will immediately cause the action associated
              with LINUX_REBOOT_CMD_RESTART.

              (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.

              (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

              (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.

              (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.

              (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.

              (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
       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         top

       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         top

       EFAULT Problem with getting user-space data under

       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         top

       reboot() is Linux-specific, and should not be used in programs
       intended to be portable.

SEE ALSO         top

       kexec_load(2), sync(2), bootparam(7), capabilities(7), ctrlaltdel(8),
       halt(8), reboot(8)

COLOPHON         top

       This page is part of release 4.13 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

Linux                            2017-09-15                        REBOOT(2)

Pages that refer to this page: systemctl(1)kexec_load(2)syscalls(2)systemd.exec(5)systemd.unit(5)capabilities(7)pid_namespaces(7)systemd-halt.service(8)