Unexpected exception while stopping nio group – How to solve this Elasticsearch error

Opster Team

Aug-23, Version: 7-8.2

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Briefly, this error occurs when Elasticsearch encounters an issue while trying to stop the NIO (Non-blocking I/O) group, which is responsible for handling network connections. This could be due to a network disruption, a bug in the software, or a system resource issue. To resolve this, you could try restarting Elasticsearch, checking for any network issues, or updating Elasticsearch to the latest version. If the problem persists, consider checking the system resources and increasing them if necessary.

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This guide will help you check for common problems that cause the log ” unexpected exception while stopping nio group ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: plugins.

Log Context

Log “unexpected exception while stopping nio group” classname is NioTransport.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :

    protected void stopInternal() {
        try {
        } catch (Exception e) {
            logger.warn("unexpected exception while stopping nio group"; e);

    protected void acceptChannel(NioSocketChannel channel) {


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