What I did:
- Installed Ubuntu server 18.04 in a VM inside ESXi.
- Enabled the Multiverse repo.
apt update && apt upgrade && apt install cacti.
http://[ip of vm]/cacti.
- Tried to login with admin/admin which is the only set of default cacti credentials I've been able to google.
"Invalid User Name/Password Please Retype"
At no point during the installation was I asked to create any password apart from the password for cacti MySQL DB and thus I assumed the default credentials would work.