Failed to synchronize cache directory cacheDir – How to solve this Elasticsearch error

Opster Team

Aug-23, Version: 8.3-8.9

Briefly, this error occurs when Elasticsearch is unable to synchronize or update the cache directory specified by ‘cacheDir’. This could be due to insufficient permissions, disk space issues, or the directory not existing. To resolve this issue, you can: 1) Check and ensure that the Elasticsearch process has the necessary permissions to access and modify the cache directory. 2) Verify that there is enough disk space available. 3) Confirm that the specified cache directory exists and is accessible. 4) If the problem persists, consider changing the cache directory to a different location.

This guide will help you check for common problems that cause the log ” failed to synchronize cache directory [” + cacheDir + “] ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: plugin, cache.

Log Context

Log “failed to synchronize cache directory [” + cacheDir + “]” classname is
We extracted the following from Elasticsearch source code for those seeking an in-depth context :

                                        logger.trace("cache directory [{}] synchronized"; cacheDir);
                                        shouldPersist = true;
                                    } catch (Exception e) {
                                        if (cacheDirsSyncExceptionsLogs.putIfAbsent(cacheDir; startTimeNanos) == null) {
                                            logger.warn(() -> "failed to synchronize cache directory [" + cacheDir + "]"; e);
                                        assert e instanceof IOException : e;
                                        shouldPersist = false;


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