Troubleshooting the VMware High Availability error: Unable to contact the primary host in a cluster
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Troubleshooting the VMware High Availability error: Unable to contact the primary host in a cluster


Article ID: 324952


Updated On:


VMware vCenter Server VMware vSphere ESXi


  • In vCenter Server, one or more ESXhosts report this error:

    Unable to contact primary host in cluster

  • VMware High Availability (HA) cannot fail over.
  • VMware HA is not working.
  • VMware HA reports this error:

    Cannot configure VMware HA


VMware ESX 4.1.x
VMware ESX Server 3.5.x
VMware ESX Server 3.0.x
VMware VirtualCenter 2.5.x
VMware ESXi 4.0.x Embedded
VMware ESXi 4.0.x Installable
VMware ESXi 3.5.x Embedded
VMware vCenter Server 4.0.x
VMware vCenter Server 4.1.x
VMware ESXi 4.1.x Embedded
VMware ESXi 4.1.x Installable
VMware ESX 4.0.x
VMware ESXi 3.5.x Installable


In some cases, ESX hosts report this error in vCenter Server.
To ensure connection to the primary VMware HA in the cluster:
  1. Re-configure VMware HA on the host that did not have the agent running.
  2. Wait for the reconfigure to complete. You receive an error similar to that generated on other hosts.
  3. From VirtualCenter, disable VMware HA on the cluster.
  4. Wait for the reconfigure to complete across all hosts.
  5. Enable VMware HA for the cluster again.
Certain versions of Virtual Infrastructure 3 have case sensitivity enforced in the network configuration files. If the preceding steps do not resolve your issue:
Note: Before you begin, refer to Restarting the Management agent on an ESX Server (1003490) for important information on restarting the mgmt-vmware service.
  1. Log in as root with SSH to each ESX host.
  2. Using a text editor, examine the contents of these three files:
    • /etc/hosts
    • /etc/sysconfig/network
    • /etc/vmware/esx.conf

  3. Change any uppercase characters to all lowercase.
  4. Save your changes and exit.
  5. Restart the Management agents on each host. To restart the agents, see Restarting the Management agents on an ESX Server (1003490).
  6. Verify the changes have taken by running the commands:

    hostname -s

    The results appear in lowercase.
For more information related to configuring VMware HA, see:

Additional Information

Troubleshooting VMware High Availability (HA) in VMware vSphere 4.x
Restarting the Management agents in ESXi
Resolución del error de VMware High Availability: no se puede contactar el host principal en un clúster
VMware High Availability エラーのトラブルシューティング:クラスタ内のプライマリ ホストにアクセスできません
对 VMware High Availability 错误“无法联系群集中的主要主机”进行故障排除