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NAME

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

SYNOPSIS

       /* For libc4 and libc5 the library call and the system call
          are identical, and 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 some of the constants involved have gotten
          symbolic names RB_*, and the library call is a 1-argument
          wrapper around the 3-argument 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  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  value  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.

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 CAP_SYS_BOOT capability is required.

CONFORMING TO

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

SEE ALSO

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

COLOPHON

       This  page  is  part of release 3.65 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.



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