man2/reboot.2

   1 .\" Copyright (c) 1998 Andries Brouwer (aeb@cwi.nl), 24 September 1998
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  22 .\" Modified, 27 May 2004, Michael Kerrisk <mtk-manpages@gmx.net>
  23 .\"     Added notes on capability requirements
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  25 .TH REBOOT 2 2004-05-27 "Linux" "Linux Programmer's Manual"
  26 .SH NAME
  27 reboot \- reboot or enable/disable Ctrl-Alt-Del
  28 .SH SYNOPSIS
  29 For libc4 and libc5 the library call and the system call are identical,
  30 and since kernel version 2.1.30 there are symbolic names
  31 LINUX_REBOOT_* for the constants and a fourth argument to the call:
  32 .sp
  33 .B #include <unistd.h>
  34 .br
  35 .B #include <linux/reboot.h>
  36 .sp
  37 .BI "int reboot(int " magic ", int " magic2 ", int " flag ", void *" arg );
  38 .sp
  39 Under glibc some of the constants involved have gotten symbolic names RB_*,
  40 and the library call is a 1-argument wrapper around the 3-argument
  41 system call:
  42 .sp
  43 .B #include <unistd.h>
  44 .br
  45 .B #include <sys/reboot.h>
  46 .sp
  47 .BI "int reboot(int " flag );
  48 .SH DESCRIPTION
  49 The
  50 .BR reboot ()
  51 call reboots the system, or enables/disables the reboot keystroke
  52 (abbreviated CAD, since the default is Ctrl-Alt-Delete;
  53 it can be changed using
  54 .BR loadkeys (1)).
  55 .PP
  56 This system call will fail (with EINVAL) unless
  57 .I magic
  58 equals LINUX_REBOOT_MAGIC1 (that is, 0xfee1dead) and
  59 .I magic2
  60 equals LINUX_REBOOT_MAGIC2 (that is, 672274793).
  61 However, since 2.1.17 also LINUX_REBOOT_MAGIC2A (that is, 85072278)
  62 and since 2.1.97 also LINUX_REBOOT_MAGIC2B (that is, 369367448)
  63 and since 2.5.71 also LINUX_REBOOT_MAGIC2C (that is, 537993216)
  64 are permitted as value for
  65 .IR magic2 .
  66 (The hexadecimal values of these constants are meaningful.)
  67 The
  68 .I flag
  69 argument can have the following values:
  70 .TP
  71 .B LINUX_REBOOT_CMD_RESTART
  72 (RB_AUTOBOOT, 0x1234567).
  73 The message `Restarting system.' is printed, and a default
  74 restart is performed immediately.
  75 If not preceded by a
  76 .BR sync (2),
  77 data will be lost.
  78 .TP
  79 .B LINUX_REBOOT_CMD_HALT
  80 (RB_HALT_SYSTEM, 0xcdef0123; since 1.1.76).
  81 The message `System halted.' is printed, and the system is halted.
  82 Control is given to the ROM monitor, if there is one.
  83 If not preceded by a
  84 .BR sync (2),
  85 data will be lost.
  86 .TP
  87 .B LINUX_REBOOT_CMD_POWER_OFF
  88 (0x4321fedc; since 2.1.30).
  89 The message `Power down.' is printed, the system is stopped,
  90 and all power is removed from the system, if possible.
  91 If not preceded by a
  92 .BR sync (2),
  93 data will be lost.
  94 .TP
  95 .B LINUX_REBOOT_CMD_RESTART2
  96 (0xa1b2c3d4; since 2.1.30).
  97 The message `Restarting system with command '%s'' is printed,
  98 and a restart (using the command string given in
  99 .IR arg )
 100 is performed immediately.
 101 If not preceded by a
 102 .BR sync (2),
 103 data will be lost.
 104 .TP
 105 .B LINUX_REBOOT_CMD_CAD_ON
 106 (RB_ENABLE_CAD, 0x89abcdef).
 107 CAD is enabled.
 108 This means that the CAD keystroke will immediately cause
 109 the action associated with LINUX_REBOOT_CMD_RESTART.
 110 .TP
 111 .B LINUX_REBOOT_CMD_CAD_OFF
 112 (RB_DISABLE_CAD, 0).
 113 CAD is disabled.
 114 This means that the CAD keystroke will cause a
 115 .B SIGINT
 116 signal to be
 117 sent to init (process 1), whereupon this process may decide upon a
 118 proper action (maybe: kill all processes, sync, reboot).
 119 .LP
 120 Only the superuser may use this function.
 121 .LP
 122 The precise effect of the above actions depends on the architecture.
 123 For the i386 architecture, the additional argument does not do
 124 anything at present (2.1.122), but the type of reboot can be
 125 determined by kernel command line arguments (`reboot=...') to be
 126 either warm or cold, and either hard or through the BIOS.
 127 .SH "RETURN VALUE"
 128 On success, zero is returned.
 129 On error, \-1 is returned, and
 130 .I errno
 131 is set appropriately.
 132 .SH ERRORS
 133 .TP
 134 .B EFAULT
 135 Problem with getting userspace data under LINUX_REBOOT_CMD_RESTART2.
 136 .TP
 137 .B EINVAL
 138 Bad magic numbers or \fIflag\fP.
 139 .TP
 140 .B EPERM
 141 The calling process has insufficient privilege to call
 142 .BR reboot ();
 143 the
 144 .B CAP_SYS_BOOT
 145 capability is required.
 146 .SH "CONFORMING TO"
 147 .BR reboot ()
 148 is Linux specific,
 149 and should not be used in programs intended to be portable.
 150 .SH "SEE ALSO"
 151 .BR sync (2),
 152 .BR bootparam (7),
 153 .BR capabilities (7),
 154 .BR ctrlaltdel (8),
 155 .BR halt (8),
 156 .BR reboot (8)