SSH and Remote Access

By the end of this lesson you'll be able to open an encrypted shell on a remote server, set up passwordless key-based login, recognise host-key prompts, and move files back and forth with scp and sftp — the everyday toolkit for working on machines you can't physically touch.

Learn SSH and Remote Access in our free Command Line course — an interactive lesson with worked examples, a practice exercise and a quick reference.

Part of the free Cli course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

1. Opening a Remote Shell

SSH (Secure Shell) gives you an encrypted command line on another machine. The basic form is ssh user@host — your username on the server, then the address. SSH uses port 22 by default; if a server listens elsewhere, add -p , as in ssh -p 2222 user@host . You can also tack a command on the end to run it remotely and return immediately.

2. Host Keys & known_hosts

The first time you connect to a server, SSH has no record of it, so it prints the server's fingerprint and asks you to confirm. Say yes only if it matches what you expect. SSH then stores that host key in ~/.ssh/known_hosts . On every later connection it compares the server's key against this file — and warns you loudly if it changed, which is how SSH catches impersonation or a man-in-the-middle attack.

3. Generating a Key Pair

Key-based auth starts with ssh-keygen -t ed25519 -C "you@example.com" , which creates a key pair : a private key ( ~/.ssh/id_ed25519 ) you keep secret, and a public key ( ~/.ssh/id_ed25519.pub ) that's safe to share. You put the public key on servers; the private key never leaves your machine — don't email it, commit it, or paste it anywhere.

4. Installing Your Public Key

To enable passwordless login, your public key needs to live on the server. ssh-copy-id user@host does this for you: it appends your .pub key to the server's ~/.ssh/authorized_keys — the file listing every public key allowed to log in as you. It asks for your password just once to do the install; after that, ssh user@host logs you in automatically with your key.

5. Host Shortcuts with ~/.ssh/config

Typing ssh -p 2222 -i ~/.ssh/id_ed25519 ada@server.example.com every time is tedious. The ~/.ssh/config file lets you save those settings under a short nickname using a Host block with HostName , User , Port , and IdentityFile . Then you just run ssh myserver . Bonus: scp and sftp read this file too.

6. Transferring Files: scp & sftp

SSH also moves files. scp (secure copy) sends them over the same encrypted channel: scp localfile user@host:/path/ copies to the remote host, scp user@host:/path/file . copies one back , and -r copies a whole directory. For an interactive session where you browse and grab files, use sftp user@host .

Fill in the blank marked ___ using the # 👉 hint, then picture the prompt you'd land on.

Two blanks: pick the key type, and the tool that installs your public key on the server. Then check the output.

No blanks this time — just a brief and an outline. Wire up a ~/.ssh/config shortcut, confirm your key is on the server, then push a release file using your new nickname. Check your result against the goal in the comments.

Practice quiz

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