ElasticSearch 5.6 cannot start on Mac OS

The provided answer is correct, however I would just like to add that you can just (re)start elasticsearch after removing the keyfile. It will detect that the file is absent and attempt to generate a new .keystore file automatically. No need to run the elasticsearch-keystore create command seperately.

The server is most probably attempting to read a newer index (org.apache.lucene.index.IndexFormatTooNewException).

Most probably the only way is to get rid of it completely with:

sudo rm -rf  /usr/local/var/lib/elasticsearch

Please double check the index and make sure you don't need the old 6.* index anymore, because you're obviously going to lose it.

I just had the same issue, and regenerating the keystore fixed the problem for me. Here are the steps I took:

Backup the existing keystore:

cd /usr/local/etc/elasticsearch/
mv elasticsearch.keystore elasticsearch.keystore.old

Generate the new keystore:

cd /usr/local/Cellar/[email protected]/5.6.15/libexec/bin/
elasticsearch-keystore create