Unknown month number – How to solve this Elasticsearch error

Opster Team

July-20, Version: 1.7-8.0

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

This guide will help you check for common problems that cause the log ” unknown month number ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: plugin.

Advanced users might want to skip right to the common problems section in each concept or try running the Check-Up to analyze Elasticsearch configuration and help resolve this error.

Log Context

Log “unknown month number [{}]”classname  is Month.java We extracted the following from Elasticsearch source code for those seeking an in-depth context :

case 9: return SEPTEMBER;
 case 10: return OCTOBER;
 case 11: return NOVEMBER;
 case 12: return DECEMBER;
 throw new ElasticsearchParseException("unknown month number [{}]"; month);
 public static Month resolve(String day) {
 switch (day.toLowerCase(Locale.ROOT)) {


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