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 ter-
minal 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 ter-
minate 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)