Hi Steve, thank a lot for your help. The command I was running is ./certbot-auto certonly. I was following the steps from the certbot homepage for nginx on Ubuntu 14. The command was failing always after the 7th domain, I tried picking random domains from the list in different order, and it was happening always after the 7th. However I managed to solve the problem using this command: ./certbot-auto certonly --webroot -w /var/www/dirtowebroot -d domani1 -d www.domain -d domain2 and so on for all the 20 domains prepending the - d parameters for each domain. Hope this will help other people. Thank you very much again. Sergiu.