man2/reboot.2

   1 .\" Copyright (c) 1998 Andries Brouwer (aeb@cwi.nl), 24 September 1998
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  25 .\" Modified, 27 May 2004, Michael Kerrisk <mtk.manpages@gmail.com>
  26 .\"     Added notes on capability requirements
  27 .\"
  28 .TH REBOOT 2 2016-10-08 "Linux" "Linux Programmer's Manual"
  29 .SH NAME
  30 reboot \- reboot or enable/disable Ctrl-Alt-Del
  31 .SH SYNOPSIS
  32 /* Since kernel version 2.1.30 there are symbolic names LINUX_REBOOT_*
  33    for the constants and a fourth argument to the call: */
  34 .PP
  35 .B #include <unistd.h>
  36 .br
  37 .B #include <linux/reboot.h>
  38 .PP
  39 .BI "int reboot(int " magic ", int " magic2 ", int " cmd ", void *" arg );
  40 .PP
  41 /* Under glibc and most alternative libc's (including uclibc, dietlibc,
  42    musl and a few others), some of the constants involved have gotten
  43    symbolic names RB_*, and the library call is a 1-argument
  44    wrapper around the system call: */
  45 .PP
  46 .B #include <unistd.h>
  47 .br
  48 .B #include <sys/reboot.h>
  49 .PP
  50 .BI "int reboot(int " cmd );
  51 .SH DESCRIPTION
  52 The
  53 .BR reboot ()
  54 call reboots the system, or enables/disables the reboot keystroke
  55 (abbreviated CAD, since the default is Ctrl-Alt-Delete;
  56 it can be changed using
  57 .BR loadkeys (1)).
  58 .PP
  59 This system call will fail (with
  60 .BR EINVAL )
  61 unless
  62 .I magic
  63 equals
  64 .B LINUX_REBOOT_MAGIC1
  65 (that is, 0xfee1dead) and
  66 .I magic2
  67 equals
  68 .B LINUX_REBOOT_MAGIC2
  69 (that is, 672274793).
  70 However, since 2.1.17 also
  71 .B LINUX_REBOOT_MAGIC2A
  72 (that is, 85072278)
  73 and since 2.1.97 also
  74 .B LINUX_REBOOT_MAGIC2B
  75 (that is, 369367448)
  76 and since 2.5.71 also
  77 .B LINUX_REBOOT_MAGIC2C
  78 (that is, 537993216)
  79 are permitted as values for
  80 .IR magic2 .
  81 (The hexadecimal values of these constants are meaningful.)
  82
  83 The
  84 .I cmd
  85 argument can have the following values:
  86 .TP
  87 .B LINUX_REBOOT_CMD_CAD_OFF
  88 .RB ( RB_DISABLE_CAD ,
  89 0).
  90 CAD is disabled.
  91 This means that the CAD keystroke will cause a
  92 .B SIGINT
  93 signal to be
  94 sent to init (process 1), whereupon this process may decide upon a
  95 proper action (maybe: kill all processes, sync, reboot).
  96 .TP
  97 .B LINUX_REBOOT_CMD_CAD_ON
  98 .RB ( RB_ENABLE_CAD ,
  99 0x89abcdef).
 100 CAD is enabled.
 101 This means that the CAD keystroke will immediately cause
 102 the action associated with
 103 .BR LINUX_REBOOT_CMD_RESTART .
 104 .TP
 105 .B LINUX_REBOOT_CMD_HALT
 106 .RB ( RB_HALT_SYSTEM ,
 107 0xcdef0123; since Linux 1.1.76).
 108 The message "System halted." is printed, and the system is halted.
 109 Control is given to the ROM monitor, if there is one.
 110 If not preceded by a
 111 .BR sync (2),
 112 data will be lost.
 113 .TP
 114 .BR LINUX_REBOOT_CMD_KEXEC
 115 .RB ( RB_KEXEC ,
 116 0x45584543, since Linux 2.6.13).
 117 Execute a kernel that has been loaded earlier with
 118 .BR kexec_load (2).
 119 This option is available only if the kernel was configured with
 120 .BR CONFIG_KEXEC .
 121 .TP
 122 .B LINUX_REBOOT_CMD_POWER_OFF
 123 .RB ( RB_POWER_OFF ,
 124 0x4321fedc; since Linux 2.1.30).
 125 The message "Power down." is printed, the system is stopped,
 126 and all power is removed from the system, if possible.
 127 If not preceded by a
 128 .BR sync (2),
 129 data will be lost.
 130 .TP
 131 .B LINUX_REBOOT_CMD_RESTART
 132 .RB ( RB_AUTOBOOT ,
 133 0x1234567).
 134 The message "Restarting system." is printed, and a default
 135 restart is performed immediately.
 136 If not preceded by a
 137 .BR sync (2),
 138 data will be lost.
 139 .TP
 140 .B LINUX_REBOOT_CMD_RESTART2
 141 (0xa1b2c3d4; since Linux 2.1.30).
 142 The message "Restarting system with command \(aq%s\(aq" is printed,
 143 and a restart (using the command string given in
 144 .IR arg )
 145 is performed immediately.
 146 If not preceded by a
 147 .BR sync (2),
 148 data will be lost.
 149 .TP
 150 .BR LINUX_REBOOT_CMD_SW_SUSPEND
 151 .RB ( RB_SW_SUSPEND ,
 152 0xd000fce1; since Linux 2.5.18).
 153 The system is suspended (hibernated) to disk.
 154 This option is available only if the kernel was configured with
 155 .BR CONFIG_HIBERNATION .
 156 .LP
 157 Only the superuser may call
 158 .BR reboot ().
 159 .LP
 160 The precise effect of the above actions depends on the architecture.
 161 For the i386 architecture, the additional argument does not do
 162 anything at present (2.1.122), but the type of reboot can be
 163 determined by kernel command-line arguments ("reboot=...") to be
 164 either warm or cold, and either hard or through the BIOS.
 165 .SS Behavior inside PID namespaces
 166 .\" commit cf3f89214ef6a33fad60856bc5ffd7bb2fc4709b
 167 .\" see also commit 923c7538236564c46ee80c253a416705321f13e3
 168 Since Linux 3.4, when
 169 .BR reboot ()
 170 is called from a PID namespace (see
 171 .BR pid_namespaces (7))
 172 other than the initial PID namespace,
 173 the effect of the call is to send a signal to the namespace "init" process.
 174 The
 175 .BR LINUX_REBOOT_CMD_RESTART
 176 and
 177 .BR LINUX_REBOOT_CMD_RESTART2
 178 .I cmd
 179 values cause a
 180 .BR SIGHUP
 181 signal to be sent.
 182 The
 183 .BR LINUX_REBOOT_CMD_POWER_OFF
 184 and
 185 .BR LINUX_REBOOT_CMD_HALT
 186 .I cmd
 187 values cause a
 188 .B SIGINT
 189 signal to be sent.
 190 For the other
 191 .I cmd
 192 values, \-1 is returned and
 193 .I errno
 194 is set to
 195 .BR EINVAL .
 196 .SH RETURN VALUE
 197 For the values of
 198 .I cmd
 199 that stop or restart the system,
 200 a successful call to
 201 .BR reboot ()
 202 does not return.
 203 For the other
 204 .I cmd
 205 values, zero is returned on success.
 206 In all cases, \-1 is returned on failure, and
 207 .I errno
 208 is set appropriately.
 209 .SH ERRORS
 210 .TP
 211 .B EFAULT
 212 Problem with getting user-space data under
 213 .BR LINUX_REBOOT_CMD_RESTART2 .
 214 .TP
 215 .B EINVAL
 216 Bad magic numbers or \fIcmd\fP.
 217 .TP
 218 .B EPERM
 219 The calling process has insufficient privilege to call
 220 .BR reboot ();
 221 the caller must have the
 222 .B CAP_SYS_BOOT
 223 inside its user namespace.
 224 .SH CONFORMING TO
 225 .BR reboot ()
 226 is Linux-specific,
 227 and should not be used in programs intended to be portable.
 228 .SH SEE ALSO
 229 .BR kexec_load (2),
 230 .BR sync (2),
 231 .BR bootparam (7),
 232 .BR capabilities (7),
 233 .BR ctrlaltdel (8),
 234 .BR halt (8),
 235 .BR reboot (8)