What cloud-init does on a new VPS
cloud-init runs once on a new VPS: datasource, user-data, default user, SSH host keys. Read the logs, and fix the fresh image that will not let you log in.
#ssh-keys
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SSH key management basics
How SSH keys work and how to manage them: one ed25519 key per device, the permissions sshd demands, config Host blocks, and revoking a lost key.