Check if FB bot is present:

grep -c "facebook.com/externalhit_uatext.php" /etc/apache2/logs/domlogs/*/*|awk -F'/' {'print $7'}|awk -F: {'print $2,$1'}|sort -k 1

Block whole FB bot network:
yum install -y whois;for i in `whois -h whois.radb.net -- '-i origin AS32934' | grep ^route |grep -v route6|awk {'print $2'}`;do csf -d $i "FB bot network https://developers.facebook.com/docs/sharing/webmasters/crawler/#crawler-rate-limits";done