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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 fail (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 sys-
            tem with command '%s'" is printed, and a restart (using the com-
            mand string given in arg) is performed immediately.  If not pre-
            ceded 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  ker-
     nel  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 EIN-
     VAL.

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.