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     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

          /* 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 hex-
          adecimal 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

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               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 config-
               ured 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 sys-
               tem." 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 aq%saq" is printed, and a
               restart (using the command string given in arg) is per-
               formed 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

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          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 names-
          pace: 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 pro-
          grams 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 5.10 of the Linux man-pages

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          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/.

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