INIT(8)

NAME
init - grandparent of all processes

DESCRIPTION
The first program started by MINIX 3 is init. The actions performed by init can be summarized by this pseudo shell program:
    # 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
The first action of init is to run /etc/rc to initialize the system as described in boot(8). Init then enters its main loop where it waits for processes to exit, and starts processes on each enabled terminal line. The file /etc/ttytab contains a list of terminal devices, their terminal types, the program to execute on them to allow one to login (usually getty(8)), and the program to execute first to initialize the line (usually 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 /sbin:/bin:/usr/sbin:/usr/bin.

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:

SIGHUP
    When receiving a hangup signal, init will forget about errors and rescan ttytab for processes to execute. Init normally rescans 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, init doesn't do that for you.

SIGTERM
    Normally sent by programs that halt or reboot MINIX 3. Causes init to stop spawning new processes.

SIGABRT
    Sent by the keyboard driver when the CTRL-ALT-DEL key combination is typed. Causes init to run the shutdown command. A second abort signal makes init halt the system directly with a system call. The keyboard driver halts the system, without a sync, after the third CTRL-ALT-DEL.

  MINIX 3 vs. Minix-vmd
There are a few differences between standard MINIX 3 and Minix-vmd on how init is run. The /etc/rc file is executed under standard MINIX 3 with input connected to /dev/console, but under Minix-vmd this is still /dev/null. This means that under Minix-vmd processes must be reconnected to /dev/console with the intr(8) program if they need user interaction. Minix-vmd passes the value of the bootopts boot variable to /etc/rc. Standard MINIX 3 does not.

FILES

/etc/ttytab
    List of terminals devices.

/etc/utmp
    List of currently logged in users.

/usr/adm/wtmp
    Login/logout history.

SEE ALSO
ttytab(5), utmp(5), getty(8), stty(1), boot(8).

AUTHOR
Kees J. Bot (kjb@cs.vu.nl)