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 /* For libc4 and libc5 the library call and the system call
  33    are identical, and since kernel version 2.1.30 there are
  34    symbolic names LINUX_REBOOT_* for the constants and a
  35    fourth argument to the call: */
  36 .sp
  37 .B #include <unistd.h>
  38 .br
  39 .B #include <linux/reboot.h>
  40 .sp
  41 .BI "int reboot(int " magic ", int " magic2 ", int " cmd ", void *" arg );
  42 .sp
  43 /* Under glibc and most alternative libc's (including uclibc, dietlibc,
  44    musl and a few others), some of the constants involved have gotten
  45    symbolic names RB_*, and the library call is a 1-argument
  46    wrapper around the system call: */
  47 .sp
  48 .B #include <unistd.h>
  49 .br
  50 .B #include <sys/reboot.h>
  51 .sp
  52 .BI "int reboot(int " cmd );
  53 .SH DESCRIPTION
  54 The
  55 .BR reboot ()
  56 call reboots the system, or enables/disables the reboot keystroke
  57 (abbreviated CAD, since the default is Ctrl-Alt-Delete;
  58 it can be changed using
  59 .BR loadkeys (1)).
  60 .PP
  61 This system call will fail (with
  62 .BR EINVAL )
  63 unless
  64 .I magic
  65 equals
  66 .B LINUX_REBOOT_MAGIC1
  67 (that is, 0xfee1dead) and
  68 .I magic2
  69 equals
  70 .B LINUX_REBOOT_MAGIC2
  71 (that is, 672274793).
  72 However, since 2.1.17 also
  73 .B LINUX_REBOOT_MAGIC2A
  74 (that is, 85072278)
  75 and since 2.1.97 also
  76 .B LINUX_REBOOT_MAGIC2B
  77 (that is, 369367448)
  78 and since 2.5.71 also
  79 .B LINUX_REBOOT_MAGIC2C
  80 (that is, 537993216)
  81 are permitted as values for
  82 .IR magic2 .
  83 (The hexadecimal values of these constants are meaningful.)
  84
  85 The
  86 .I cmd
  87 argument can have the following values:
  88 .TP
  89 .B LINUX_REBOOT_CMD_CAD_OFF
  90 .RB ( RB_DISABLE_CAD ,
  91 0).
  92 CAD is disabled.
  93 This means that the CAD keystroke will cause a
  94 .B SIGINT
  95 signal to be
  96 sent to init (process 1), whereupon this process may decide upon a
  97 proper action (maybe: kill all processes, sync, reboot).
  98 .TP
  99 .B LINUX_REBOOT_CMD_CAD_ON
 100 .RB ( RB_ENABLE_CAD ,
 101 0x89abcdef).
 102 CAD is enabled.
 103 This means that the CAD keystroke will immediately cause
 104 the action associated with
 105 .BR LINUX_REBOOT_CMD_RESTART .
 106 .TP
 107 .B LINUX_REBOOT_CMD_HALT
 108 .RB ( RB_HALT_SYSTEM ,
 109 0xcdef0123; since Linux 1.1.76).
 110 The message "System halted." is printed, and the system is halted.
 111 Control is given to the ROM monitor, if there is one.
 112 If not preceded by a
 113 .BR sync (2),
 114 data will be lost.
 115 .TP
 116 .BR LINUX_REBOOT_CMD_KEXEC
 117 .RB ( RB_KEXEC ,
 118 0x45584543, since Linux 2.6.13).
 119 Execute a kernel that has been loaded earlier with
 120 .BR kexec_load (2).
 121 This option is available only if the kernel was configured with
 122 .BR CONFIG_KEXEC .
 123 .TP
 124 .B LINUX_REBOOT_CMD_POWER_OFF
 125 .RB ( RB_POWER_OFF ,
 126 0x4321fedc; since Linux 2.1.30).
 127 The message "Power down." is printed, the system is stopped,
 128 and all power is removed from the system, if possible.
 129 If not preceded by a
 130 .BR sync (2),
 131 data will be lost.
 132 .TP
 133 .B LINUX_REBOOT_CMD_RESTART
 134 .RB ( RB_AUTOBOOT ,
 135 0x1234567).
 136 The message "Restarting system." is printed, and a default
 137 restart is performed immediately.
 138 If not preceded by a
 139 .BR sync (2),
 140 data will be lost.
 141 .TP
 142 .B LINUX_REBOOT_CMD_RESTART2
 143 (0xa1b2c3d4; since Linux 2.1.30).
 144 The message "Restarting system with command \(aq%s\(aq" is printed,
 145 and a restart (using the command string given in
 146 .IR arg )
 147 is performed immediately.
 148 If not preceded by a
 149 .BR sync (2),
 150 data will be lost.
 151 .TP
 152 .BR LINUX_REBOOT_CMD_SW_SUSPEND
 153 .RB ( RB_SW_SUSPEND ,
 154 0xd000fce1; since Linux 2.5.18).
 155 The system is suspended (hibernated) to disk.
 156 This option is available only if the kernel was configured with
 157 .BR CONFIG_HIBERNATION .
 158 .LP
 159 Only the superuser may call
 160 .BR reboot ().
 161 .LP
 162 The precise effect of the above actions depends on the architecture.
 163 For the i386 architecture, the additional argument does not do
 164 anything at present (2.1.122), but the type of reboot can be
 165 determined by kernel command-line arguments ("reboot=...") to be
 166 either warm or cold, and either hard or through the BIOS.
 167 .SS Behavior inside PID namespaces
 168 .\" commit cf3f89214ef6a33fad60856bc5ffd7bb2fc4709b
 169 .\" see also commit 923c7538236564c46ee80c253a416705321f13e3
 170 Since Linux 3.4, when
 171 .BR reboot ()
 172 is called from a PID namespace (see
 173 .BR pid_namespaces (7))
 174 other than the initial PID namespace,
 175 the effect of the call is to send a signal to the namespace "init" process.
 176 The
 177 .BR LINUX_REBOOT_CMD_RESTART
 178 and
 179 .BR LINUX_REBOOT_CMD_RESTART2
 180 .I cmd
 181 values cause a
 182 .BR SIGHUP
 183 signal to be sent.
 184 The
 185 .BR LINUX_REBOOT_CMD_POWER_OFF
 186 and
 187 .BR LINUX_REBOOT_CMD_HALT
 188 .I cmd
 189 values cause a
 190 .B SIGINT
 191 signal to be sent.
 192 For the other
 193 .I cmd
 194 values, \-1 is returned and
 195 .I errno
 196 is set to
 197 .BR EINVAL .
 198 .SH RETURN VALUE
 199 For the values of
 200 .I cmd
 201 that stop or restart the system,
 202 a successful call to
 203 .BR reboot ()
 204 does not return.
 205 For the other
 206 .I cmd
 207 values, zero is returned on success.
 208 In all cases, \-1 is returned on failure, and
 209 .I errno
 210 is set appropriately.
 211 .SH ERRORS
 212 .TP
 213 .B EFAULT
 214 Problem with getting user-space data under
 215 .BR LINUX_REBOOT_CMD_RESTART2 .
 216 .TP
 217 .B EINVAL
 218 Bad magic numbers or \fIcmd\fP.
 219 .TP
 220 .B EPERM
 221 The calling process has insufficient privilege to call
 222 .BR reboot ();
 223 the caller must have the
 224 .B CAP_SYS_BOOT
 225 inside its user namespace.
 226 .SH CONFORMING TO
 227 .BR reboot ()
 228 is Linux-specific,
 229 and should not be used in programs intended to be portable.
 230 .SH SEE ALSO
 231 .BR kexec_load (2),
 232 .BR sync (2),
 233 .BR bootparam (7),
 234 .BR capabilities (7),
 235 .BR ctrlaltdel (8),
 236 .BR halt (8),
 237 .BR reboot (8)