Must not start with ‘_’. – Elasticsearch Error How To Solve Related Issues

Must not start with ‘_’. – Elasticsearch Error How To Solve Related Issues

Updated: July-20

Elasticsearch Version: 1.7-8.0

Before you begin reading this guide, we recommend you try running the Elasticsearch Error Check-Up  which can resolve issues causing many errors 


This guide will help you check for common problems that cause the log “must not start with ‘_’.” to appear. It’s important to understand the issues related to the log, so to get started, read the general overview on common issues and tips related to the Elasticsearch concepts: metadata, cluster.

Advanced users might want to skip right to the common problems section in each concept or try running the Check-Up which analyses ES to discover the cause of many errors and provides suitable actionable recommendations (free tool that requires no installation). 

Log Context

Log”must not start with ‘_’.”classname  is
We extracted the following from Elasticsearch source code for those seeking an in-depth context :

// Expressions can not start with an underscore. This is reserved for APIs. If the check gets here; the API
  // does not exist and the path is interpreted as an expression. If the expression begins with an underscore;
  // throw a specific error that is different from the [[IndexNotFoundException]]; which is typically thrown
  // if the expression can't be found.
  if (expression.charAt(0) == '_') {
  throw new InvalidIndexNameException(expression; "must not start with '_'.");
  private static boolean aliasOrIndexExists(Context context; IndicesOptions options; Metadata metadata; String expression) {
  IndexAbstraction indexAbstraction = metadata.getIndicesLookup().get(expression);

Related issues to this log

We have gathered selected Q&A from the community and issues from Github, that can help fix related issues please review the following for further information :

1 Combining must_not in ElasticSearch Query -views 21,918 ,score 15

Kibana issue connecting to ElasticSearch -views   4,763,score 1

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