.\" Copyright (c) 1980 Regents of the University of California.
.\" All rights reserved.  The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\"
.\"	@(#)init.8	6.2 (Berkeley) 5/22/86
.\"
.TH INIT 8 "May 22, 1986"
.UC 4
.SH NAME
init \- process control initialization
.SH SYNOPSIS
.B /etc/init
.SH DESCRIPTION
.I Init
is invoked inside UNIX as the last step in the boot procedure.
It normally then runs the automatic reboot sequence as described in
.IR reboot (8),
and if this succeeds, begins multi-user operation.
If the reboot fails, it commences single user operation by giving
the super-user a shell on the console.  It is possible to pass parameters
from the boot program to
.I init
so that single user operation is commenced immediately.
When such single user operation is terminated by killing the single-user
shell (i.e. by hitting ^D),
.I init
runs
.I /etc/rc
without the reboot parameter.
This command file
performs housekeeping operations
such as removing temporary files,
mounting file systems, and starting
daemons.
.PP
In multi-user operation, 
.I init's
role is to create a process for each
terminal port on which a user may log in.
To begin such operations, it reads the file
.I /etc/ttys
and
executes a command for each terminal specified in the file.
This command will usually be
.IR /etc/getty .
.I Getty
opens and initializes the terminal line,
reads the user's name and invokes
.I login
to log in the user and execute the Shell.
.PP
Ultimately the Shell will terminate
because of an end-of-file either
typed explicitly or generated as a result of hanging up.
The main path of
.IR init ,
which has been waiting
for such an event,
wakes up and removes the appropriate entry from the
file
.IR utmp ,
which records current users, and
makes an entry in
.IR /usr/adm/wtmp ,
which maintains a history
of logins and logouts.
The
.I wtmp
entry is made only if a user logged in successfully on the line.
Then the appropriate terminal is reopened and
.I getty
is
reinvoked.
.PP
.I Init
catches the
.I hangup
signal (signal SIGHUP) and interprets it to mean that
the file
.I /etc/ttys
should be read again.
The Shell process on each line which used to be active
in
.I ttys
but is no longer there is terminated;
a new process is created for each added line;
lines unchanged in the file are undisturbed.
Thus it is possible to drop or add terminal lines without
rebooting the system by changing the
.I ttys
file and sending a
.I hangup
signal to the
.I init
process: use `kill \-HUP 1.'
.PP
.I Init
will terminate multi-user operations and resume single-user mode
if sent a terminate (TERM) signal, i.e. ``kill \-TERM 1''.
If there are processes outstanding which are deadlocked (due to
hardware or software failure),
.I init
will not wait for them all to die (which might take forever), but
will time out after 30 seconds and print a warning message.
.PP
.I Init
will cease creating new
.IR getty 's
and allow the system to slowly die away, if it is sent a terminal stop (TSTP)
signal, i.e. ``kill \-TSTP 1''.  A later hangup will resume full
multi-user operations, or a terminate will initiate a single user shell.
This hook is used by
.IR reboot (8)
and
.IR halt (8).
.PP
.I Init's
role is so critical that if it dies, the system will reboot itself
automatically.
If, at bootstrap time, the
.I init
process cannot be located, the system will loop in user mode at location
0x13.
.SH DIAGNOSTICS
\fB/etc/getty\fP \fIgettyargs\fP\fB failing, sleeping\fP.
A process being started to service a line is exiting quickly
each time it is started.
This is often caused by a ringing or noisy terminal line.
.I Init will sleep for 30 seconds, then continue trying to start the process.
.LP
\fBWARNING: Something is hung (wont die); ps axl advised\fR.  A process
is hung and could not be killed when the system was shutting down.
This is usually caused by a process
which is stuck in a device driver due to a persistent device error condition.
.SH FILES
/dev/console,
/dev/tty*,
/etc/utmp,
/usr/adm/wtmp,
/etc/ttys,
/etc/rc
.SH "SEE ALSO"
login(1), kill(1), sh(1), ttys(5), crash(8V), getty(8), rc(8), reboot(8),
halt(8), shutdown(8)