Well, I'm on AIX, but this should be applicable.
First, you'll need to write 2 scripts, start_informix and stop_informix
mine is pretty simple...
start_informix
<code>
#!/bin/ksh
#
# Script to start the Informix Database and ISA Server.
#
echo "\nStarting the Informix Database .. \c"
/usr/informix/bin/oninit
if [ "$?" -eq "0" ]
then
echo "OK"
else
echo "FAILED"
fi
echo "\nStarting the ISA HTTP Server .... \c"
/usr/informix/ISA/sbin/isactl start
if [ "$?" -eq "0" ]
then
echo "OK\n"
else
echo "FAILED\n"
fi
exit 0
</code>
stop_informix
<code>
#!/bin/ksh
#
# Script to shutdown the Informix Server.
#
echo "\nShutting down Informix Server..."
su - informix -c "/usr/informix/bin/onmode -ky"
if [ "$?" -eq "0" ]
then
echo "\nInformix Server shutdown - OK"
else
echo "\nInformix Server shutdown - FAILED"
fi
</code>
Both scripts assume that you have INFORMIXDIR set correctly. Put both scripts somewhere accessible by informix.
Then, modify /etc/inittab to have the line...
informix:2: once: su - informix -c "start_informix"
and modify /etc/rc.shutdown to have the line...
su - informix -c "stop_informix"
(/etc/rc.shutdown may be empty before you start, this is not (that) unusual).