GPDB : SSH permission denied (public key) - greenplum

Question

When trying to ssh (from greenplum system user) one of datanode from Master gpdb host.
env - gpdb 4.3.10
Getting error
[gpadmin#mdw ~]$ ssh datanode
Permission denied (publickey,gssapi-keyex,gssapi-with-mic).
[gpadmin#mdw ~]$
WE Tried
Tried on pivotal docs
https://discuss.pivotal.io/hc/en-us/articles/203777546-gpssh-exkeys-Fails-with-Error-Permission-denied-During-Local-Key-Exchange
Also, observed node not able to SSH any of data node/master host.
**Here is verbose mode -v with SSH info**
debug1: Host 'datanode01' is known and matches the ECDSA host key.
debug1: Found key in /home/gpadmin/.ssh/known_hosts:3
debug1: ssh_ecdsa_verify: signature correct
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic
debug1: Next authentication method: gssapi-keyex
debug1: No valid Key exchange context
debug1: Next authentication method: gssapi-with-mic
debug1: Unspecified GSS failure. Minor code may provide more information
No Kerberos credentials available
debug1: Unspecified GSS failure. Minor code may provide more information
No Kerberos credentials available
debug1: Unspecified GSS failure. Minor code may provide more information
debug1: Unspecified GSS failure. Minor code may provide more information
No Kerberos credentials available
debug1: Next authentication method: publickey
debug1: Offering RSA public key: /home/gpadmin/.ssh/id_rsa
debug1: Authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic
debug1: Trying private key: /home/gpadmin/.ssh/id_dsa
debug1: Trying private key: /home/gpadmin/.ssh/id_ecdsa
debug1: Trying private key: /home/gpadmin/.ssh/id_ed25519
debug1: No more authentication methods to try.
Permission denied (publickey,gssapi-keyex,gssapi-with-mic)

Answer 1

I think the problem isn't the root login as that doc suggests but rather, password authentication is disabled. Try running this on ALL nodes:
sudo sed -i 's/PasswordAuthentication no/PasswordAuthentication yes/' /etc/ssh/sshd_config
sudo service sshd restart
echo "gpadmin:changeme" | sudo chpasswd
Then retry gpssh-exkeys as gpadmin.
gpssh-exkey -f all_hosts
After you exchange the keys, you can disable password authentication again.
sudo sed -i 's/PasswordAuthentication yes/PasswordAuthentication no/' /etc/ssh/sshd_config