systemctl --all list-timers
 
systemctl stop    certbot.timer
systemctl disable certbot.timer
systemctl mask    certbot.timer
 
m=$(( RANDOM % 60 )); h=$(( RANDOM % 24 )); d=$(( RANDOM % 7 ))
echo "## Let's Encrypt SSL certificate renewal with certbot" | tee -a /etc/crontab
echo "$m $h * * $d root /usr/bin/certbot -q renew"           | tee -a /etc/crontab
 
# dom=$(( 1+ RANDOM % 31 )) mon=$(( 1+ RANDOM % 12 ))