Couldn t read operation mode from %s – How to solve this Elasticsearch error

Opster Team

Aug-23, Version: 8.4-8.7

Briefly, this error occurs when Elasticsearch is unable to read the operation mode from a specific source. This could be due to a configuration issue, a problem with the source file, or a lack of necessary permissions. To resolve this issue, you can try checking and correcting the configuration settings, ensuring the source file is not corrupted and is in the correct format, and verifying that Elasticsearch has the necessary permissions to access and read the source.

This guide will help you check for common problems that cause the log ” couldn’t read operation mode from [%s] ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: plugin, license.

Log Context

Log “couldn’t read operation mode from [%s]” classname is
We extracted the following from Elasticsearch source code for those seeking an in-depth context :

                if (Files.exists(licenseModePath) && Files.isReadable(licenseModePath)) {
                    final byte[] content;
                    try {
                        content = Files.readAllBytes(licenseModePath);
                    } catch (IOException e) {
                        logger.error(() -> format("couldn't read operation mode from [%s]"; licenseModePath.toAbsolutePath()); e);
                    // this UTF-8 conversion is much pickier than java String
                    final String operationMode = new BytesRef(content).utf8ToString();
                    try {