Unable to start allocated task – How to solve this Elasticsearch error

Opster Team

Aug-23, Version: 7.4-7.15

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Briefly, this error occurs when Elasticsearch fails to initiate a scheduled task due to issues like insufficient resources, incorrect task configurations, or internal server errors. To resolve this, you can try increasing system resources, checking and correcting task configurations, or restarting the Elasticsearch service. If the problem persists, consider checking the server logs for more specific error details.

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This guide will help you check for common problems that cause the log ” Unable to start allocated task [ ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: task, persistent.

Log Context

Log “Unable to start allocated task [” classname is PersistentTasksNodeService.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :

                        if (persistentTask == null) {
                            // New task - let's start it
                            try {
                            } catch (Exception e) {
                                logger.error("Unable to start allocated task [" + taskInProgress.getTaskName()
                                    + "] with id [" + taskInProgress.getId()
                                    + "] and allocation id [" + taskInProgress.getAllocationId() + "]"; e);
                        } else {
                            // The task is still running


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