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 2017-09-15 "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
  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 fails (with the error
  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 .PP
  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 .PP
 157 Only the superuser may call
 158 .BR reboot ().
 159 .PP
 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 .\"
 166 .SS Behavior inside PID namespaces
 167 .\" commit cf3f89214ef6a33fad60856bc5ffd7bb2fc4709b
 168 .\" see also commit 923c7538236564c46ee80c253a416705321f13e3
 169 Since Linux 3.4,
 170 if
 171 .BR reboot ()
 172 is called
 173 from a PID namespace other than the initial PID namespace
 174 with one of the
 175 .I cmd
 176 values listed below,
 177 it performs a "reboot" of that namespace:
 178 the "init" process of the PID namespace is immediately terminated,
 179 with the effects described in
 180 .BR pid_namespaces (7).
 181 .PP
 182 The values that can be supplied in
 183 .I cmd
 184 when calling
 185 .BR reboot ()
 186 in this case are as follows:
 187 .TP
 188 .BR LINUX_REBOOT_CMD_RESTART ", " LINUX_REBOOT_CMD_RESTART2
 189 The "init" process is terminated,
 190 and
 191 .BR wait (2)
 192 in the parent process reports that the child was killed with a
 193 .B SIGHUP
 194 signal.
 195 .TP
 196 .BR LINUX_REBOOT_CMD_POWER_OFF ", " LINUX_REBOOT_CMD_HALT
 197 The "init" process is terminated,
 198 and
 199 .BR wait (2)
 200 in the parent process reports that the child was killed with a
 201 .B SIGINT
 202 signal.
 203 .PP
 204 For the other
 205 .I cmd
 206 values,
 207 .BR reboot ()
 208 returns \-1 and
 209 .I errno
 210 is set to
 211 .BR EINVAL .
 212 .SH RETURN VALUE
 213 For the values of
 214 .I cmd
 215 that stop or restart the system,
 216 a successful call to
 217 .BR reboot ()
 218 does not return.
 219 For the other
 220 .I cmd
 221 values, zero is returned on success.
 222 In all cases, \-1 is returned on failure, and
 223 .I errno
 224 is set appropriately.
 225 .SH ERRORS
 226 .TP
 227 .B EFAULT
 228 Problem with getting user-space data under
 229 .BR LINUX_REBOOT_CMD_RESTART2 .
 230 .TP
 231 .B EINVAL
 232 Bad magic numbers or \fIcmd\fP.
 233 .TP
 234 .B EPERM
 235 The calling process has insufficient privilege to call
 236 .BR reboot ();
 237 the caller must have the
 238 .B CAP_SYS_BOOT
 239 inside its user namespace.
 240 .SH CONFORMING TO
 241 .BR reboot ()
 242 is Linux-specific,
 243 and should not be used in programs intended to be portable.
 244 .SH SEE ALSO
 245 .BR systemctl (1),
 246 .BR systemd (1),
 247 .BR kexec_load (2),
 248 .BR sync (2),
 249 .BR bootparam (7),
 250 .BR capabilities (7),
 251 .BR ctrlaltdel (8),
 252 .BR halt (8),
 253 .BR shutdown (8)