The -bD command-line switch is almost exactly the same as the -bd switch. That is, it causes sendmail to run as a daemon, but unlike the -bd switch, it prevents sendmail from performing a fork(2) and thereby keeps sendmail in the foreground. The -bD switch also prevents detaching from the controlling terminal (just as does the -d99.100 debugging switch, -d99.100).

This -bD command-line switch allows sendmail to be run from a "wrapper" script—for example, to detect whether it died or was killed:

#!/bin/sh
SENDMAIL=/usr/sbin/sendmail
UCBMAIL=/usr/ucb/mail

if [ -f $SENDMAIL -a -f $UCBMAIL ]
then
        $SENDMAIL -bD -q1h
        echo ${SENDMAIL}, which should run forever, died \
                | $UCBMAIL -s "Sendmail died" root
fi

Note that the echo line will never be reached as long as sendmail continues to run. Also note that you will not be able to restart sendmail in the usual manner with a SIGHUP if you use this script.