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1.1 root 1: .TH INIT 8 "1 April 1981"
2: .UC 4
3: .SH NAME
4: init \- process control initialization
5: .SH SYNOPSIS
6: .B /etc/init
7: .SH DESCRIPTION
8: .I Init
9: is invoked inside UNIX as the last step in the boot procedure.
10: It normally then runs the automatic reboot sequence as described in
11: .IR reboot (8),
12: and if this succeeds, begins multi-user operation.
13: If the reboot fails, it commences single user operation by giving
14: the super-user a shell on the console. It is possible to pass parameters
15: from the boot program to
16: .I init
17: so that single user operation is commenced immediately.
18: When such single user operation is terminated by killing the single-user
19: shell (i.e. by hitting ^D),
20: .I init
21: runs
22: .I /etc/rc
23: without the reboot parameter.
24: This command file
25: performs housekeeping operations
26: such as removing temporary files,
27: mounting file systems, and starting
28: daemons.
29: .PP
30: In multi-user operation,
31: .I init's
32: role is to create a process for each
33: terminal port on which a user may log in.
34: To begin such operations, it reads the file
35: .I /etc/ttys
36: and
37: forks several times to create a process
38: for each terminal specified in the file.
39: Each of these processes opens the appropriate terminal
40: for reading and writing. These channels thus
41: receive file descriptors 0, 1 and 2, the standard input and
42: output and the diagnostic output.
43: Opening the terminal will usually involve a delay,
44: since the
45: .IR open ""
46: is not completed until someone
47: is dialed up and carrier established on the channel.
48: If a terminal exists but an error occurs when trying to open the terminal
49: .I init
50: complains by writing a message to the system console;
51: the message is repeated every 10 minutes for each such terminal
52: until the terminal is shut off in /etc/ttys and init notified (by
53: a hangup, as described below), or the terminal becomes accessible
54: (init checks again every minute).
55: After an open succeeds,
56: .I /etc/getty
57: is called with argument as specified by the second character of
58: the
59: .I ttys
60: file line.
61: .I Getty
62: reads the user's name and invokes
63: .I login
64: to log in the user and execute the Shell.
65: .PP
66: Ultimately the Shell will terminate
67: because of an end-of-file either
68: typed explicitly or generated as a result of hanging up.
69: The main path of
70: .IR init ,
71: which has been waiting
72: for such an event,
73: wakes up and removes the appropriate entry from the
74: file
75: .IR utmp ,
76: which records current users, and
77: makes an entry in
78: .IR /usr/adm/wtmp ,
79: which maintains a history
80: of logins and logouts.
81: The
82: .I wtmp
83: entry is made only if a user logged in successfully on the line.
84: Then the appropriate terminal is reopened and
85: .I getty
86: is
87: reinvoked.
88: .PP
89: .I Init
90: catches the
91: .I hangup
92: signal (signal SIGHUP) and interprets it to mean that
93: the file
94: .I /etc/ttys
95: should be read again.
96: The Shell process on each line which used to be active
97: in
98: .I ttys
99: but is no longer there is terminated;
100: a new process is created for each added line;
101: lines unchanged in the file are undisturbed.
102: Thus it is possible to drop or add phone lines without
103: rebooting the system by changing the
104: .I ttys
105: file and sending a
106: .I hangup
107: signal to the
108: .I init
109: process: use `kill \-HUP 1.'
110: .PP
111: .I Init
112: will terminate multi-user operations and resume single-user mode
113: if sent a terminate (TERM) signal, i.e. ``kill \-TERM 1''.
114: If there are processes outstanding which are deadlocked (due to
115: hardware or software failure),
116: .I init
117: will not wait for them all to die (which might take forever), but
118: will time out after 30 seconds and print a warning message.
119: .PP
120: .I Init
121: will cease creating new
122: .IR getty 's
123: and allow the system to slowly die away, if it is sent a terminal stop (TSTP)
124: signal, i.e. ``kill \-TSTP 1''. A later hangup will resume full
125: multi-user operations, or a terminate will initiate a single user shell.
126: This hook is used by
127: .IR reboot (8)
128: and
129: .IR halt (8).
130: .PP
131: .I Init's
132: role is so critical that if it dies, the system will reboot itself
133: automatically.
134: If, at bootstrap time, the
135: .I init
136: process cannot be located, the system will loop in user mode at location
137: 0x13.
138: .SH DIAGNOSTICS
139: \fBinit: \fR\fItty\fR\|\fB: cannot open\fR. A terminal which is turned
140: on in the \fIrc\fR file cannot be opened, likely because the requisite
141: lines are either not configured into the system or the associated device
142: was not attached during boot-time system configuration.
143: .LP
144: \fBWARNING: Something is hung (wont die); ps axl advised\fR. A process
145: is hung and could not be killed when the system was shutting down.
146: This is usually caused by a process
147: which is stuck in a device driver due to a persistent device error condition.
148: .SH FILES
149: /dev/console,
150: /dev/tty*,
151: /etc/utmp,
152: /usr/adm/wtmp,
153: /etc/ttys,
154: /etc/rc
155: .SH "SEE ALSO"
156: login(1), kill(1), sh(1), ttys(5), getty(8), rc(8), reboot(8),
157: halt(8), shutdown(8)
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