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

COLOPHON
       This page is part of release 5.03 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                             2019-03-06                         REBOOT(2)