SSH (Secure Shell)

When you will meet it

Deploying, running models on cloud GPUs, or managing an always-on server all require it. It is also the answer to "how does my agent act on another machine".

Minimal example

ssh user@203.0.113.10          # 連線（首次會問你信不信這台機器）
ssh -i ~/.ssh/my_key user@host # 指定要用哪把私鑰
scp report.pdf user@host:~/    # 順手把檔案送過去

The first connection asks you to confirm a fingerprint and type yes before it remembers the host. That is normal man-in-the-middle protection, not an error.

What people get wrong

• Handing over or committing the private key. The private key never leaves your machine; the public key is what you give away.
• Leaving password login on, or having ~/.ssh permissions too open. With loose permissions the server silently refuses your key and the error rarely says so.