monitor.sh

#!/bin/bash

function send_email () {
    echo sending email;
}

mongo --eval "db.stats()" > /dev/null  # do a simple harmless command of some sort

RESULT=$?   # returns 0 if mongo eval succeeds

if [ $RESULT -ne 0 ]; then
    send_email
    `systemctl start mongodb`
    exit 1
else
    echo "mongodb running!"
fi