To copy a ssh key to a DO droplet, you temporarily enable password login for the sshd daemon.
Log in as root:
Edit ssh config:
sudo nano /etc/ssh/sshd_config
Change this line:
PasswordAuthentication no
to
PasswordAuthentication yes
Restart daemon:
sudo systemctl restart sshd
Then run the below to copy the generated ssh key to the acount named test.
Note that ssh port is 5225.
You will be prompted for the UNIX password for user test:
ssh-copy-id -p 5225 -i .ssh/id_rsa.pub [email protected]
Then revert the ssh daemon changes by changing the ssh config line to:
PasswordAuthentication no
Restart daemon:
sudo systemctl restart sshd
To connect to the droplet, with port 5225:
ssh [email protected] -p 5225
More information at DigitalOcean.