Bash while read line

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LEARN ABOUT MINIX

init

INIT(8) 						      System Manager's Manual							   INIT(8)

NAME

       init - grandparent of all processes

DESCRIPTION

       The first program started by Minix 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.  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 vs. Minix-vmd
       There  are  a  few  differences between standard Minix and Minix-vmd on how init is run.  The /etc/rc file is executed under standard Minix
       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 program if they need user interaction.  Minix-vmd passes the value of the bootopts boot variable
       to /etc/rc.  Standard Minix 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)

																	   INIT(8)

Shell Programming and Scripting