I started with an empty Solr instance and Firefox 38 on Linux. This is the trunk source..
There's a 'No cores available. Go and create one' button available in the old and the new UI. In the old UI, clicking it goes to the core admin, and pops open the dialog for Add Core. The new UI only goes to the core admin. Also, when you then click on the Add Core, the dialog bleeds into the sidebar. I then started with a getting started config and a cloud of 2x2. Then brought up admin UI on one of them, opened up one of the cores, and clicked on the Files tab -- that showed an exception.. {"data":{"responseHeader":{"status":500,"QTime":1},"error":{"msg":"Path must not end with / character","trace":"java.lang.IllegalArgumentException: Path must not end with / character\n\tat org.apache.zookeeper.common.PathUtils.validatePath(PathUtils.java:58)\n\tat org.apache.zookeeper.ZooKeeper.exists(ZooKeeper.java:1024)\n\tat org.apache.solr.common.cloud.SolrZkClient$5.execute(SolrZkClient.java:319)\n\tat org.apache.solr.common.cloud.SolrZkClient$5.execute(SolrZkClient.java:316)\n\tat org.apache.solr.common.cloud.ZkCmdExecutor.retryOperation(ZkCmdExecutor.java:61)\n\tat org.apache.solr.common.cloud.SolrZkClient.exists(SolrZkClient.java:316)\n\tat org.apache.solr.handler.admin.ShowFileRequestHandler.getAdminFileFromZooKeeper(ShowFileRequestHandler.java:324)\n\tat org.apache.solr.handler.admin.ShowFileRequestHandler.showFromZooKeeper(ShowFileRequestHandler.java:148)\n\tat org.apache.solr.handler.admin.ShowFileRequestHandler.handleRequestBody(ShowFileRequestHandler.java:135)\n\tat org.apache.solr.handler.RequestHandlerBase.handleRequest(RequestHandlerBase.java:143)\n\tat org.apache.solr.core.SolrCore.execute(SolrCore.java:2057)\n\tat org.apache.solr.servlet.HttpSolrCall.execute(HttpSolrCall.java:648)\n\tat org.apache.solr.servlet.HttpSolrCall.call(HttpSolrCall.java:452)\n\tat org.apache.solr.servlet.SolrDispatchFilter.doFilter(SolrDispatchFilter.java:227)\n\tat org.apache.solr.servlet.SolrDispatchFilter.doFilter(SolrDispatchFilter.java:196)\n\tat org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1652)\n\tat org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:585)\n\tat org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:143)\n\tat org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:577)\n\tat Moving to Plugins/Stats, and then Core, and selecting the first searcher entry (e.g. for me, it is Searcher@3a7bd1[gettingstarted_shard1_replica1] main), I see stats like: - searcherName:Searcher@​3a7bd1[gettingstarted_shard1_replica1] main - reader: ExitableDirectoryReader(​UninvertingDirectoryReader(​)) Notice the unescaped characters there..