A BASH script to monitor a log and restart a service if idle.

restart-svc-on-log-failure.sh

#!/bin/bash
set -x
PATH=$PATH:/opt/scripts
SERVICE=ethminer

# start infinite loop
while :
do

SECS=$(date +%s)
idletime=$(expr $SECS - $(date +%s -r /tmp/ethminer.log))

if [ "$idletime" -gt 120 ]
then
        echo "Restarting service due to no activity for 2 minutes! ($idletime seconds)"
        sudo service $SERVICE restart    # restart or send mail etc here
        sleep 60
fi
# loop repeats until ctrl-c:
sleep 30
done

Execute with sudo or as root to put the script in background:
screen -dmSL log-monitor ./restart-svc-on-log-failure.sh