Just did this:
to change the hostname permanently, you need to change it in two places:
vi /etc/sysconfig/network
NETWORKING=yes
HOSTNAME=newHostName
and: a good idea if you have any applications that need to resolve the IP of the hostname)
vi /etc/hosts
127.0.0.1 newHostName
127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4
::1 localhost localhost.localdomain localhost6 localhost6.localdomain6
and then
rebooting the system
should I try the /opt/letsencrypt/letsencrypt-auto --apache -d example.com -d www.example.com command again?