init - grandparent of all processes
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
echo reboot >>/usr/adm/wtmp
while :; do
# Wait for a process to exit, but don't always block.
# Record logout. (Not in this dumb way, of course.)
if "pid is in my tables" $pid
echo "logout $pid" >/etc/utmp
echo "logout $pid" >>/usr/adm/wtmp
# Start a new session.
while read line type getty init
if idle $line
$init ... <$tty >$tty
$getty <$tty >$tty 2>&1 &
"add pid to tables" $pid
echo "login $line $pid" >/etc/utmp
echo "login $line $pid" >>/usr/adm/wtmp
done < /dev/ttytab
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:
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.
Normally sent by programs that halt or reboot Minix. Causes init to
stop spawning new processes.
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
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.
/etc/ttytab List of terminals devices.
/etc/utmp List of currently logged in users.
/usr/adm/wtmp Login/logout history.
ttytab(5), utmp(5), getty(8), stty(1), boot(8).
Kees J. Bot (email@example.com)