SSH permission issue - failed to add host to known hosts (/home/username/.ssh/known_hosts)

 The permission set on the .ssh folder, the private keys and public keys matter. To solve the problem of -

Failed to add the host to the list of known hosts (/home/username/.ssh/known_hosts)

.ssh folder - permission set to 700
public keys (id_rsa.pub or id_dsa.pub)- permission set to 644
private keys (id_rsa or id_dsa)- permission set to 600