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@gmail.com>
  23 .\"     Added notes on capability requirements
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  25 .TH REBOOT 2 2008-02-11 "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
  30    are identical, and since kernel version 2.1.30 there are
  31    symbolic names LINUX_REBOOT_* for the constants and a
  32    fourth argument to the call: */
  33 .sp
  34 .B #include <unistd.h>
  35 .br
  36 .B #include <linux/reboot.h>
  37 .sp
  38 .BI "int reboot(int " magic ", int " magic2 ", int " cmd ", void *" arg );
  39 .sp
  40 /* Under glibc some of the constants involved have gotten
  41    symbolic names RB_*, and the library call is a 1-argument
  42    wrapper around the 3-argument system call: */
  43 .sp
  44 .B #include <unistd.h>
  45 .br
  46 .B #include <sys/reboot.h>
  47 .sp
  48 .BI "int reboot(int " cmd );
  49 .SH DESCRIPTION
  50 The
  51 .BR reboot ()
  52 call reboots the system, or enables/disables the reboot keystroke
  53 (abbreviated CAD, since the default is Ctrl-Alt-Delete;
  54 it can be changed using
  55 .BR loadkeys (1)).
  56 .PP
  57 This system call will fail (with
  58 .BR EINVAL )
  59 unless
  60 .I magic
  61 equals
  62 .B LINUX_REBOOT_MAGIC1
  63 (that is, 0xfee1dead) and
  64 .I magic2
  65 equals
  66 .B LINUX_REBOOT_MAGIC2
  67 (that is, 672274793).
  68 However, since 2.1.17 also
  69 .B LINUX_REBOOT_MAGIC2A
  70 (that is, 85072278)
  71 and since 2.1.97 also
  72 .B LINUX_REBOOT_MAGIC2B
  73 (that is, 369367448)
  74 and since 2.5.71 also
  75 .B LINUX_REBOOT_MAGIC2C
  76 (that is, 537993216)
  77 are permitted as value for
  78 .IR magic2 .
  79 (The hexadecimal values of these constants are meaningful.)
  80 The
  81 .I cmd
  82 argument can have the following values:
  83 .TP
  84 .B LINUX_REBOOT_CMD_RESTART
  85 (RB_AUTOBOOT, 0x1234567).
  86 The message "Restarting system." is printed, and a default
  87 restart is performed immediately.
  88 If not preceded by a
  89 .BR sync (2),
  90 data will be lost.
  91 .TP
  92 .B LINUX_REBOOT_CMD_HALT
  93 (RB_HALT_SYSTEM, 0xcdef0123; since 1.1.76).
  94 The message "System halted." is printed, and the system is halted.
  95 Control is given to the ROM monitor, if there is one.
  96 If not preceded by a
  97 .BR sync (2),
  98 data will be lost.
  99 .TP
 100 .B LINUX_REBOOT_CMD_POWER_OFF
 101 (0x4321fedc; since 2.1.30).
 102 The message "Power down." is printed, the system is stopped,
 103 and all power is removed from the system, if possible.
 104 If not preceded by a
 105 .BR sync (2),
 106 data will be lost.
 107 .TP
 108 .B LINUX_REBOOT_CMD_RESTART2
 109 (0xa1b2c3d4; since 2.1.30).
 110 The message "Restarting system with command '%s'" is printed,
 111 and a restart (using the command string given in
 112 .IR arg )
 113 is performed immediately.
 114 If not preceded by a
 115 .BR sync (2),
 116 data will be lost.
 117 .TP
 118 .B LINUX_REBOOT_CMD_CAD_ON
 119 (RB_ENABLE_CAD, 0x89abcdef).
 120 CAD is enabled.
 121 This means that the CAD keystroke will immediately cause
 122 the action associated with
 123 .BR LINUX_REBOOT_CMD_RESTART .
 124 .TP
 125 .B LINUX_REBOOT_CMD_CAD_OFF
 126 (RB_DISABLE_CAD, 0).
 127 CAD is disabled.
 128 This means that the CAD keystroke will cause a
 129 .B SIGINT
 130 signal to be
 131 sent to init (process 1), whereupon this process may decide upon a
 132 proper action (maybe: kill all processes, sync, reboot).
 133 .LP
 134 Only the superuser may call
 135 .BR reboot ().
 136 .LP
 137 The precise effect of the above actions depends on the architecture.
 138 For the i386 architecture, the additional argument does not do
 139 anything at present (2.1.122), but the type of reboot can be
 140 determined by kernel command-line arguments (`reboot=...') to be
 141 either warm or cold, and either hard or through the BIOS.
 142 .SH "RETURN VALUE"
 143 For the values of
 144 .I cmd
 145 that stop or restart the system,
 146 a successful call to
 147 .BR reboot ()
 148 does not return.
 149 For the other
 150 .I cmd
 151 values, zero is returned on success.
 152 In all cases, \-1 is returned on failure, and
 153 .I errno
 154 is set appropriately.
 155 .SH ERRORS
 156 .TP
 157 .B EFAULT
 158 Problem with getting userspace data under
 159 .BR LINUX_REBOOT_CMD_RESTART2 .
 160 .TP
 161 .B EINVAL
 162 Bad magic numbers or \fIcmd\fP.
 163 .TP
 164 .B EPERM
 165 The calling process has insufficient privilege to call
 166 .BR reboot ();
 167 the
 168 .B CAP_SYS_BOOT
 169 capability is required.
 170 .SH "CONFORMING TO"
 171 .BR reboot ()
 172 is Linux-specific,
 173 and should not be used in programs intended to be portable.
 174 .SH "SEE ALSO"
 175 .BR sync (2),
 176 .BR bootparam (7),
 177 .BR capabilities (7),
 178 .BR ctrlaltdel (8),
 179 .BR halt (8),
 180 .BR reboot (8)