We can set the "Hadoop Group" during installation by using the customize services => Misc tab. How to change it post-install ?
The Hadoop Group can be changed with the following command:
-u admin -p admin set localhost cluster_name cluster-env user_group new_group
This assumes it is running from the Ambari host with the default credentials. Replace cluster_name with the name of the cluster.
Details here: https://cwiki.apache.org/confluence/display/AMBARI/Update+Service-Accounts+After+Install
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