Setting ssh connectivity on a new machine. Just so that I remember.

On SSH client:

ssh-keygen

scp ~\.ssh\id_ed25519.pub user@host:/tmp/user.pub

ssh user@host

mkdir -p ~/.ssh

cat /tmp/user.pub >> ~/.ssh/authorized_keys

chmod 700 ~/.ssh

chmod 600 ~/.ssh/authorized_keys

exit

ssh user@host

Key passphrase prompt should appear instead of the password prompt. Unless the key is not encrypted, then it should just log in.

sudo nano /etc/sshd_config

Ensure:

PasswordAuthentication no
PermitRootLogin no
PubkeyAuthentication yes

sudo systemctl restart ssh

Done.