Currently the main node in your cluster is offline so you want to promote a standby node to the main role.

From the command line on the standby node you want to promote run a check to get the cluster Id:

opc cluster node list
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The screenshot shows the main node is offline, in this instance we are going to make the host 192.168.100.60 the new main. The * next to the hostname indicates which node you are currently logged onto. Make a note of the nodes Id, in this case 0d31f1e7-d49d-4970-8b67-b9b7c1e8de20.

We now run the following command to promote the selected node:

opc cluster node promote -i 
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For our example the command would be:

opc cluster node promote -i 0d31f1e7-d49d-4970-8b67-b9b7c1e8de20
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Finally check the node list again to check the node has been promoted to the main role:

opc cluster node list
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You will also notice the offline node has been removed from the cluster.