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At the prompt type: ssh -i /home/asterisk/.ssh/id_rsa root@SecondaryServerIP
If all went well, you should now be logged in to the Secondary server.We can use the below method to copy the SSH keys to the Secondary (Warm spare) server.
In FreePBX UI > Admin > Backup & Restore > Global Settings, we have an option to copy key and paste in other PBX systems > Backup & Restore > Global Settings > Public key of other system. This key is copied to the file “authorized_keys” in the path “/home/asterisk/.ssh”