--- title: "Cloud Hadoop troubleshooting" slug: "cloudhadoop-vpc-troubleshoot" updated: 2026-09-17T09:18:10Z published: 2026-09-17T09:18:10Z canonical: "guide.ncloud-docs.com/cloudhadoop-vpc-troubleshoot" stale: true --- > ## Documentation Index > Fetch the complete documentation index at: https://guide.ncloud-docs.com/llms.txt > Use this file to discover all available pages before exploring further. # Cloud Hadoop troubleshooting Available in VPC You might run into the following problems when using Cloud Hadoop. Find out causes and possible solutions. ## Out of Memory (OOM) event An OOM event caused the server to hang. #### Cause If system memory usage increases rapidly, the kernel's OOM Killer is triggered and terminates processes that consume large amounts of memory. If a kernel process is terminated as a result, the server may hang. #### Solution **What to do when the server hangs** Contact [Customer Support](https://www.ncloud.com/support/question/service) to request a VM reboot. **How to prevent server hangs** - Configure ping checks and process monitoring to periodically check the node status. - Scale out edge nodes or master nodes that run jobs to distribute the load. - Scale up edge nodes or master nodes that run jobs to distribute the load. ## Change the node specifications to scale up the memory capacity. The cluster does not operate normally after changing the configuration in Ambari. #### Cause When you change the configuration through Ambari, related settings may be unintentionally affected, causing the cluster to malfunction. #### Solution Ambari stores cluster configurations and version numbers in order of modification time. You can roll back to a version from before the cluster malfunctioned and restart the cluster. The following instructions describe how to roll back the HDFS configuration to a previous version. 1. In Ambari, navigate to **All Services** > **HDFS** > **Configs**. 2. Click ![cloudhadoop-vpc-troubleshoot-icon](https://cdn.document360.io/6998976f-9d95-4df8-b847-d375892b92c2/Images/Documentation/cloudhadoop-vpc-troubleshoot-icon.png?sv=2026-02-06&spr=https&st=2026-10-27T13%3A39%3A41Z&se=2026-10-27T14%3A39%3A41Z&sr=c&sp=r&sig=pyhJOXmmnHo3L5I8ykECRZUhCtq%2BIqFh7nMPxSqqN5o%3D) to compare it with the previous version. ![cloudhadoop-vpc-troubleshoot-ambariconfig01](https://cdn.document360.io/6998976f-9d95-4df8-b847-d375892b92c2/Images/Documentation/cloudhadoop-vpc-troubleshoot-ambariconfig01.png?sv=2026-02-06&spr=https&st=2026-10-27T13%3A39%3A41Z&se=2026-10-27T14%3A39%3A41Z&sr=c&sp=r&sig=pyhJOXmmnHo3L5I8ykECRZUhCtq%2BIqFh7nMPxSqqN5o%3D) 3. Check the comparison between Version 2 (working configuration) and Version 3 (malfunctioning configuration). ![cloudhadoop-vpc-troubleshoot-ambariconfig02.png](https://cdn.document360.io/6998976f-9d95-4df8-b847-d375892b92c2/Images/Documentation/cloudhadoop-vpc-troubleshoot-ambariconfig02.png?sv=2026-02-06&spr=https&st=2026-10-27T13%3A39%3A41Z&se=2026-10-27T14%3A39%3A41Z&sr=c&sp=r&sig=pyhJOXmmnHo3L5I8ykECRZUhCtq%2BIqFh7nMPxSqqN5o%3D) 4. Click **Version 2**, the version to apply. 5. Click **[MAKE CURRENT]** to roll back to the previous settings. ![cloudhadoop-vpc-troubleshoot-ambariconfig03.png](https://cdn.document360.io/6998976f-9d95-4df8-b847-d375892b92c2/Images/Documentation/cloudhadoop-vpc-troubleshoot-ambariconfig03.png?sv=2026-02-06&spr=https&st=2026-10-27T13%3A39%3A41Z&se=2026-10-27T14%3A39%3A41Z&sr=c&sp=r&sig=pyhJOXmmnHo3L5I8ykECRZUhCtq%2BIqFh7nMPxSqqN5o%3D) 6. Check that a new version number has been assigned, and then click **[RESTART]**. ![cloudhadoop-vpc-troubleshoot-ambariconfig04.png](https://cdn.document360.io/6998976f-9d95-4df8-b847-d375892b92c2/Images/Documentation/cloudhadoop-vpc-troubleshoot-ambariconfig04.png?sv=2026-02-06&spr=https&st=2026-10-27T13%3A39%3A41Z&se=2026-10-27T14%3A39%3A41Z&sr=c&sp=r&sig=pyhJOXmmnHo3L5I8ykECRZUhCtq%2BIqFh7nMPxSqqN5o%3D) ## Lost password for Ambari account The password for the Ambari account has been forgotten. #### Cause The cluster administrator account or password entered when the cluster was created has been forgotten. #### Solution See [Reset cluster administrator password](/docs/en/hadoop-vpc-4#%ED%81%B4%EB%9F%AC%EC%8A%A4%ED%84%B0%EA%B4%80%EB%A6%AC%EC%9E%90%ED%8C%A8%EC%8A%A4%EC%9B%8C%EB%93%9C%EC%B4%88%EA%B8%B0%ED%99%94) to reset the password. ## Cannot access Zeppelin Notebook Zeppelin Notebook cannot be accessed while using a Spark cluster. #### Cause - Zeppelin Notebook is not running. - SSH tunneling is configured incorrectly. #### Solution - Access the Ambari Web UI and check that Zeppelin Notebook is running properly. - See [Web UI](/docs/en/hadoop-vpc-7#WEBUI%EC%A0%91%EC%86%8D). - If Zeppelin Notebook is running properly but cannot be accessed, check the tunneling settings. - See [Access the Web UI with tunneling](/docs/en/hadoop-vpc-6). ## Report security vulnerabilities The security.datanode.protocol.acl setting is set to *, which has been reported as a security vulnerability. #### Cause security.datanode.protocol.acl is a property key that specifies the users and groups that can access DataNodes. By default, "*" is set to allow access by all users, but you can change the permissions manually. #### Solution Starting with Cloud Hadoop 2.3, the security.datanode.protocol.acl setting is provided as `hdfs hadoop`. For clusters created with an earlier version of Cloud Hadoop or clusters currently running with `*`, you can modify the rules for specifying users and groups that can access DataNodes as follows. - Separate users and groups with a space ( ). - Separate users in the user list and groups in the group list with commas (,). Example: The following rule allows the users alice and bob and the groups users and wheel. `alice,bob users,wheel` Users automatically created for each component in Cloud Hadoop are included in the hadoop group, so you can configure the setting as follows. `security.datanode.protocol.acl=hdfs,custom_user1,custom_user2 hadoop,custom_group1,custom_group2` ## Learning resources We offer various materials for you to explore. To learn more about Cloud Hadoop, check out these helpful links: - FAQs: [Cloud Hadoop FAQs](https://www.ncloud.com/support/faq/prod?categoryCode2=ANALY&categoryCode3=SV_0086&page=1) - API guide: [Cloud Hadoop API guide](https://api.ncloud-docs.com/docs/en/analytics-vhadoop) - NAVER Cloud Platform's blog: [Cloud Hadoop - Apache Iceberg and Apache NiFi available](https://blog.naver.com/n_cloudplatform/223272470476?trackingCode=blog_bloghome_searchlist) - NAVER Cloud Platform's blog: [Cloud Hadoop, a big data analytics platform made even more powerful with Notebook features!](https://blog.naver.com/n_cloudplatform/223272470476?trackingCode=blog_bloghome_searchlist) Note If you're still having trouble finding what you need, click on the feedback icon and send us your thoughts and requests. We'll use your feedback to improve this guide.