init.8

操作系统设计与实现源码

.TH INIT 8
.SH NAME
init \- grandparent of all processes
.SH DESCRIPTION
The first program started by Minix is
.BR init .
The actions performed by
.B init
can be summarized by this pseudo shell program:
.RS
.nf
.if t .ft C

# Open 0, 1, 2.
exec </dev/null >/dev/log 2>&1

# Run the system initialization script.
sh /etc/rc $bootopts

>/etc/utmp
echo reboot >>/usr/adm/wtmp

while :; do
	# Wait for a process to exit, but don't always block.
	wait

	# Record logout.  (Not in this dumb way, of course.)
	if "pid is in my tables" $pid
	then
		echo "logout $pid" >/etc/utmp
		echo "logout $pid" >>/usr/adm/wtmp
	fi

	# Start a new session.
	while read line type getty init
	do
		if idle $line
		then
			$init ... <$tty >$tty
			$getty <$tty >$tty 2>&1 &
			pid=$!
			"add pid to tables" $pid
			echo "login $line $pid" >/etc/utmp
			echo "login $line $pid" >>/usr/adm/wtmp
		fi
	done < /dev/ttytab
done

.if t .ft R
.fi
.RE
The first action of
.B init
is to run
.B /etc/rc
to initialize the system as described in
.BR boot (8).
.B Init
then enters its main loop where it waits for processes to exit, and starts
processes on each enabled terminal line.  The file
.B /etc/ttytab
contains a list of terminal devices, their terminal types, the program to
execute on them to allow one to login (usually
.BR getty (8)),
and the program to execute first to initialize the line (usually
.BR stty (1)).
These fields may be left out to indicate that a line is disabled or that
initialization is not necessary.  The commands are searched using the path
.BR /sbin:/bin:/usr/sbin:/usr/bin .
.PP
.B Init
accepts several signals that must be sent to process id 1.  (It is the first
process, so natually its process id is 1.)  The signals are:
.TP
.B SIGHUP
When receiving a hangup signal,
.B init
will forget about errors and rescan
.B ttytab
for processes to execute.
.B Init
normally rescans
.B ttytab
each time it feels the need to respawn a process, so the hangup signal is only
needed if a line has been shut down, or after a terminate signal.  Note
that after turning a line off you will have to kill the process running on
that line manually,
.B init
doesn't do that for you.
.TP
.B SIGTERM
Normally sent by programs that halt or reboot Minix.  Causes
.B init
to stop spawning new processes.
.TP
.B SIGABRT
Sent by the keyboard driver when the
.B CTRL-ALT-DEL
key combination is typed.  Causes
.B init
to run the
.B shutdown
command.  A second abort signal makes
.B init
halt the system directly with a system call.  The keyboard driver halts the
system, without a sync, after the third CTRL-ALT-DEL.
.SS "Minix vs. Minix-vmd"
There are a few differences between standard Minix and Minix-vmd on how
.B init
is run.  The
.B /etc/rc
file is executed under standard Minix with input connected to
.BR /dev/console ,
but under Minix-vmd this is still
.BR /dev/null .
This means that under Minix-vmd processes must be reconnected to
.B /dev/console
with the
.B intr
program if they need user interaction.
Minix-vmd passes the value of the
.B bootopts
boot variable to /etc/rc.  Standard Minix does not.
.SH FILES
.TP 25n
.B /etc/ttytab
List of terminals devices.
.TP
.B /etc/utmp
List of currently logged in users.
.TP
.B /usr/adm/wtmp
Login/logout history.
.SH "SEE ALSO"
.BR ttytab (5),
.BR utmp (5),
.BR getty (8),
.BR stty (1),
.BR boot (8).
.SH AUTHOR
Kees J. Bot ([e-mail])