INIT(8)INIT(8)NAMEinit - 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 com‐
mands 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 res‐
cans 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 combina‐
tion is typed. Causes init to run the shutdown command. A sec‐
ond abort signal makes init halt the system directly with a sys‐
tem 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 recon‐
nected 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 ALSOttytab(5), utmp(5), getty(8), stty(1), boot(8).
AUTHOR
Kees J. Bot (kjb@cs.vu.nl)
INIT(8)
