Passwordless SSH access

1. Check for existing SSH keys

# ls ~/.ssh

2. Generate new SSH keys

# ssh-keygen

3. Check for SSH keys

# ls ~/.ssh

4. Copy your pulic key to server

# ssh-copy-id <username>@<ip-address>

or

# cat ~/.ssh/id_rsa.pub | ssh <username>@<ip-address> 'mkdir -p ~/.ssh && cat >> ~/.ssh/authorized_keys' 

Refer to:
1. https://www.raspberrypi.org/documentation/remote-access/ssh/passwordless.md
2. https://askubuntu.com/questions/46930/how-can-i-set-up-password-less-ssh-login