yes ambari agent is running in my namenode .Please find the command
sudo su -l hdfs -c 'hdfs dfsadmin -safemode enter'
sudo su hdfs -l -c 'hdfs dfsadmin -saveNamespace'
I know it's an old question, but I'm sure other people have run into it in the last year.
I just ran into this same problem. I was able to solve it by disabling the firewall on the server that the wizard asked me to initiate the checkpoint from. Within a second or two, the next button was enabled.
No guarantee that this will fix the problem for other people, but if you haven't tried temporarily disabling the firewall, it might help.
Does anyone know what port is used for this process?