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2 .\" The Regents of the University of California. All rights reserved.
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4 .\" This code is derived from software contributed to Berkeley by
5 .\" Donn Seeley at Berkeley Software Design, Inc.
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31 .\" @(#)init.8 8.3 (Berkeley) 4/18/94
32 .\" $FreeBSD: src/sbin/init/init.8,v 1.22.2.11 2003/05/03 22:19:20 keramida Exp $
33 .\"
34 .Dd September 29, 2016
35 .Dt INIT 8
36 .Os
37 .Sh NAME
38 .Nm init
39 .Nd process control initialization
40 .Sh SYNOPSIS
41 .Nm
42 .Nm
43 .Oo
44 .Cm 0 | 1 | 6 |
45 .Cm c | q
46 .Oc
47 .Sh DESCRIPTION
48 The
49 .Nm
50 utility
51 is the last stage of the boot process.
52 It normally runs the automatic reboot sequence as described in
53 .Xr rc 8 ,
54 and if this succeeds, begins multi-user operation.
55 If the reboot scripts fail,
56 .Nm
57 commences single-user operation by giving
58 the super-user a shell on the console.
59 The
60 .Nm
61 utility may be passed parameters
62 from the boot program to
63 prevent the system from going multi-user and to instead execute
64 a single-user shell without starting the normal daemons.
65 The system is then quiescent for maintenance work and may
66 later be made to go to multi-user by exiting the
67 single-user shell (with ^D).
68 This
69 causes
70 .Nm
71 to run the
72 .Pa /etc/rc
73 start up command file in fastboot mode (skipping disk checks).
74 .Pp
75 If the
76 .Em console
77 entry in the
78 .Xr ttys 5
79 file is marked
80 .Dq insecure ,
81 then
82 .Nm
83 will require that the super-user password be
84 entered before the system will start a single-user shell.
85 The password check is skipped if the
86 .Em console
87 is marked as
88 .Dq secure .
89 .Pp
90 The kernel runs with five different levels of security.
91 Any super-user process can raise the security level, but no process
92 can lower it.
93 The security levels are:
94 .Bl -tag -width flag
95 .It Ic -1
96 Permanently insecure mode \- always run the system in level 0 mode.
97 This is the default initial value.
98 .It Ic 0
99 Insecure mode \- immutable and append-only flags may be turned off.
100 All devices may be read or written subject to their permissions.
101 .It Ic 1
102 Secure mode \- the system immutable and system append-only flags may not
103 be turned off;
104 disks for mounted file systems,
105 .Pa /dev/mem ,
106 and
107 .Pa /dev/kmem
108 may not be opened for writing;
109 kernel modules (see
110 .Xr kld 4 )
111 may not be loaded or unloaded.
112 .It Ic 2
113 Highly secure mode \- same as secure mode, plus disks may not be
114 opened for writing (except by
115 .Xr mount 2 )
116 whether mounted or not.
117 This level precludes tampering with file systems by unmounting them,
118 but also inhibits running
119 .Xr newfs 8
120 while the system is multi-user.
121 .Pp
122 In addition, kernel time changes are restricted to less than or equal to one
123 second. Attempts to change the time by more than this will log the message
124 .Dq Time adjustment clamped to +1 second .
125 .It Ic 3
126 Network secure mode \- same as highly secure mode, plus
127 IP packet filter rules (see
128 .Xr ipfw 8
129 and
130 .Xr ipfirewall 4 )
131 cannot be changed and
132 .Xr dummynet 4
133 configuration cannot be adjusted.
134 .El
135 .Pp
136 If the security level is initially nonzero, then
137 .Nm
138 leaves it unchanged.
139 Otherwise,
140 .Nm
141 raises the level to 1 before going multi-user for the first time.
142 Since the level cannot be reduced, it will be at least 1 for
143 subsequent operation, even on return to single-user.
144 If a level higher than 1 is desired while running multi-user,
145 it can be set before going multi-user, e.g., by the startup script
146 .Xr rc 8 ,
147 using
148 .Xr sysctl 8
149 to set the
150 .Va kern.securelevel
151 variable to the required security level.
152 .Pp
153 In multi-user operation,
154 .Nm
155 maintains
156 processes for the terminal ports found in the file
157 .Xr ttys 5 .
158 The
159 .Nm
160 utility reads this file and executes the command found in the second field,
161 unless the first field refers to a device in
162 .Pa /dev
163 which is not configured.
164 The first field is supplied as the final argument to the command.
165 This command is usually
166 .Xr getty 8 ;
167 .Nm getty
168 opens and initializes the tty line
169 and
170 executes the
171 .Xr login 1
172 program.
173 The
174 .Nm login
175 program, when a valid user logs in,
176 executes a shell for that user. When this shell
177 dies, either because the user logged out
178 or an abnormal termination occurred (a signal),
179 the
180 .Nm
181 utility wakes up, deletes the user
182 from the
183 .Xr utmp 5
184 file of current users and records the logout in the
185 .Xr wtmp 5
186 file.
187 The cycle is
188 then restarted by
189 .Nm
190 executing a new
191 .Nm getty
192 for the line.
193 .Pp
194 The
195 .Nm
196 utility can also be used to keep arbitrary daemons running,
197 automatically restarting them if they die.
198 In this case, the first field in the
199 .Xr ttys 5
200 file must not reference the path to a configured device node
201 and will be passed to the daemon
202 as the final argument on its command line.
203 This is similar to the facility offered in the
204 .At V
205 .Pa /etc/inittab .
206 .Pp
207 Line status (on, off, secure, getty, or window information)
208 may be changed in the
209 .Xr ttys 5
210 file without a reboot by sending the signal
211 .Dv SIGHUP
212 to
213 .Nm
214 with the command
215 .Dq Li "kill -HUP 1" .
216 On receipt of this signal,
217 .Nm
218 re-reads the
219 .Xr ttys 5
220 file.
221 When a line is turned off in
222 .Xr ttys 5 ,
223 .Nm
224 will send a
225 .Dv SIGHUP
226 signal to the controlling process for the session associated with the line.
227 For any lines that were previously turned off in the
228 .Xr ttys 5
229 file and are now on,
230 .Nm
231 executes the command specified in the second field.
232 If the command or window field for a line is changed,
233 the change takes effect at the end of the current
234 login session (e.g., the next time
235 .Nm
236 starts a process on the line).
237 If a line is commented out or deleted from
238 .Xr ttys 5 ,
239 .Nm
240 will not do anything at all to that line.
241 However, it will complain that the relationship between lines
242 in the
243 .Xr ttys 5
244 file and records in the
245 .Xr utmp 5
246 file is out of sync,
247 so this practice is not recommended.
248 .Pp
249 The
250 .Nm
251 utility will terminate multi-user operations and resume single-user mode
252 if sent a terminate
253 .Pq Dv TERM
254 signal, for example,
255 .Dq Li "kill \-TERM 1" .
256 If there are processes outstanding that are deadlocked (because of
257 hardware or software failure),
258 .Nm
259 will not wait for them all to die (which might take forever), but
260 will time out after 30 seconds and print a warning message.
261 .Pp
262 The
263 .Nm
264 utility will cease creating new processes
265 and allow the system to slowly die away, if it is sent a terminal stop
266 .Pq Dv TSTP
267 signal, i.e.\&
268 .Dq Li "kill \-TSTP 1" .
269 A later hangup will resume full
270 multi-user operations, or a terminate will start a single-user shell.
271 This hook is used by
272 .Xr reboot 8
273 and
274 .Xr halt 8 .
275 .Pp
276 The
277 .Nm
278 utility will terminate all possible processes (again, it will not wait
279 for deadlocked processes) and reboot the machine if sent the interrupt
280 .Pq Dv INT
281 signal, i.e.\&
282 .Dq Li "kill \-INT 1".
283 This is useful for shutting the machine down cleanly from inside the kernel
284 or from X when the machine appears to be hung.
285 .Pp
286 The
287 .Nm
288 utility will do the same, except it will halt the machine if sent
289 the user defined signal 1
290 .Pq Dv USR1 ,
291 or will halt and turn the power off (if hardware permits) if sent
292 the user defined signal 2
293 .Pq Dv USR2 .
294 .Pp
295 When shutting down the machine,
296 .Nm
297 will try to run the
298 .Pa /etc/rc.shutdown
299 script.
300 This script can be used to cleanly terminate specific programs such
301 as
302 .Nm innd
303 (the InterNetNews server).
304 If this script does not terminate within 120 seconds,
305 .Nm
306 will terminate it. The timeout can be configured via the
307 .Xr sysctl 8
308 variable
309 .Va kern.init_shutdown_timeout .
310 .Pp
311 The role of
312 .Nm
313 is so critical that if it dies, the system will reboot itself
314 automatically.
315 If, at bootstrap time, the
316 .Nm
317 process cannot be located, the system will panic with the message
318 .Dq "panic: init died (signal %d, exit %d)" .
319 .Pp
320 If run as a user process as shown in the second synopsis line,
321 .Nm
322 will emulate
323 .At V
324 behavior, i.e. super-user can specify the desired
325 .Em run-level
326 on a command line, and
327 .Nm
328 will signal the original
329 (PID 1)
330 .Nm
331 as follows:
332 .Bl -column Run-level SIGTERM
333 .It Sy "Run-level Signal Action"
334 .It Cm 0 Ta Dv SIGUSR2 Ta "Halt and turn the power off"
335 .It Cm 1 Ta Dv SIGTERM Ta "Go to single-user mode"
336 .It Cm 6 Ta Dv SIGINT Ta "Reboot the machine"
337 .It Cm c Ta Dv SIGTSTP Ta "Block further logins"
338 .It Cm q Ta Dv SIGHUP Ta Rescan the
339 .Xr ttys 5
340 file
341 .El
342 .Sh FILES
343 .Bl -tag -width /etc/rc.shutdown -compact
344 .It Pa /dev/console
345 system console device
346 .It Pa /dev/tty*
347 terminal ports found in
348 .Xr ttys 5
349 .It Pa /var/run/utmp
350 record of current users on the system
351 .It Pa /var/log/wtmp
352 record of all logins and logouts
353 .It Pa /etc/ttys
354 the terminal initialization information file
355 .It Pa /etc/rc
356 system startup commands
357 .It Pa /etc/rc.shutdown
358 system shutdown commands
359 .El
360 .Sh DIAGNOSTICS
361 .Bl -diag
362 .It "getty repeating too quickly on port %s, sleeping."
363 A process being started to service a line is exiting quickly
364 each time it is started.
365 This is often caused by a ringing or noisy terminal line.
366 .Bf -emphasis
367 Init will sleep for 30 seconds,
368 then continue trying to start the process.
369 .Ef
370 .It "some processes would not die; ps axl advised."
371 A process
372 is hung and could not be killed when the system was shutting down.
373 This condition is usually caused by a process
374 that is stuck in a device driver because of
375 a persistent device error condition.
376 .El
377 .Sh SEE ALSO
378 .Xr kill 1 ,
379 .Xr login 1 ,
380 .Xr sh 1 ,
381 .Xr dummynet 4 ,
382 .Xr ipfirewall 4 ,
383 .Xr kld 4 ,
384 .Xr ttys 5 ,
385 .Xr crash 8 ,
386 .Xr getty 8 ,
387 .Xr halt 8 ,
388 .Xr ipfw 8 ,
389 .Xr rc 8 ,
390 .Xr reboot 8 ,
391 .Xr shutdown 8 ,
392 .Xr sysctl 8
393 .Sh HISTORY
394 An
395 .Nm
396 utility appeared in
397 .At v1 .
398 .Sh CAVEATS
399 Systems without
400 .Xr sysctl 8
401 behave as though they have security level \-1.
402 .Pp
403 Setting the security level above 1 too early in the boot sequence can
404 prevent
405 .Xr fsck 8
406 from repairing inconsistent file systems. The
407 preferred location to set the security level is at the end of
408 .Pa /etc/rc
409 after all multi-user startup actions are complete.