Go into the directory where the core file is located (this is version 6.6.0), stop solr, run the repair command and finally start solr again:

<code>
cd /opt/solr-6.6.0/server/solr-webapp/webapp/WEB-INF/lib/
invoke-rc.d solr stop
java -cp lucene-core-6.6.0.jar -ea:org.apache.lucene... org.apache.lucene.index.CheckIndex "/var/solr/data/dovecot/data/index" -exorcise
invoke-rc.d solr start
</code>

Note that "-ea:org.apache.lucene..." is the literal value of the parameter.

The parameter "/var/solr/data/dovecot/data/index" describes the path to the index called "dovecot".