ssh permission denied (publickey). ubuntu code example

Example 1: ssh error permission denied (publickey)

sudo nano /etc/ssh/sshd_config
PermitRootLogin prohibit-password to PermitRootLogin yes 
PasswordAuthentication no to PasswordAuthentication yes

Example 2: permission denied (publickey password)

cat ~/.ssh/id_rsa.pub | ssh <user>@<hostname> 'cat >> .ssh/authorized_keys && echo "Key copied"'