reboot(2) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | SEE ALSO | COLOPHON

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 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         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 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         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 to indicate the error.

ERRORS         top

       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         top

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

SEE ALSO         top

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

COLOPHON         top

       This page is part of release 5.11 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                          2021-03-22                      REBOOT(2)

Pages that refer to this page: systemctl(1)kexec_load(2)syscalls(2)org.freedesktop.login1(5)systemd.exec(5)systemd.unit(5)capabilities(7)pid_namespaces(7)systemd-halt.service(8)