The problem is about the omeka core. I copied solr-core/omeka to /home/user/bin/solr-6.4.1/server/solr and restarted Solr but the new core is not recognized. I tried also to put it with /home/user/bin/solr-6.4.1/example/cloud/ without success.
Is there something to do to install the omeka core?
So far with how to access the solr administration interface.
I know this is not probably the answer you were looking for, but it might give you an insight on how others are doing it. Also, I think this course might help with Solr Administration Interface.