I noticed slight differences in the Solr version for Sitecore 9 update 1. Here 6.6.1 is mentioned whereas the installation guide has 6.6.2. Does the initial 9 release need 6.6.1 and update 1 requires 6.6.2?
Do not use SOLR 6.6.1 due to a Solr Bug that has been identified.
Use SOLR 6.6.2, which is the recommended version. The KB article has not been updated to reflect this except in footnote:
Solr server can try to initialize a Solr core twice, resulting in the following error:
> org.apache.solr.common.SolrException: Unable to create core > [core_name] ... Caused by: > org.apache.lucene.store.LockObtainFailedException: Lock held by this > virtual machine: > C:\solr-6.6.1\server\solr\core_name\data\index\write.lock The error is > caused by a Solr bug: SOLR-11297
The issue does not affect Sitecore functionality and can be ignored. To resolve the issue, upgrade Solr to 6.6.2.