copy SSH key to a remote server

If you are adding it to a server where you can login with a username/password, use ssh-copy-id:

ssh-copy-id -i ~/.ssh/my-key.pub user@hostname

But if you only login with an existing SSH key, you’ll need to do it manually:

cat ~/.ssh/my-new-key.pub | ssh -i ~/.ssh/my-old-key user@hostname 'cat >> .ssh/authorized_keys'

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