Are you trying to execute ./splunk start from the right path?
It seems like a permission issue or you are trying to start services of Splunk from low user privileges.
Warning: cannot create "/opt/splunk/etc/licenses/enterprise"
So, Splunk was not able to "create" the file.. Splunk user should have correct access to the /opt/splunk directory.
please reply us the "ls -l /opt/" so that we can have a look about the /opt/splunk directory permissions.
may be permission issues.