In case of unclean shutdown mongo fail to start, but returns exit code 0.
Exit code matters when used in startup scripts.
Look at this piece of code from my ArchLinux's mongodb startup script. Here we try to start mongo an then check exit code. Mongo should return correct exit codes.
[ -z "$PID" ] && /bin/su mongodb -s /bin/bash -c "/usr/bin/mongod --config /etc/mongodb.conf &" > /var/log/mongod 2>&1
if [ $? -gt 0 ]; then
stat_fail
else
add_daemon mongodb
stat_done
fi