Using ssh without a password involves encryption keys – a public key and a private key – to authenticate you. Those keys are usually stored in ~/.ssh/. Though they can go anywhere else, too - just have to tell ssh where to find them.

~/.ssh/id_rsa
~/.ssh/id_rsa.pub

The contents of those keys are really simple, too. One of them is the text representation of large number, whose size is measured in bits – the number of digits in the number, if it was converted to binary. That is the private key.

For instance: I can create a new key really easily, with an empty password:

ssh-keygen -N '' -f demokey

That creates two files, ./demokey and ./demokey.pub. You want to share the public key, and keep the private one…private. The default names, which you should expect and use, are id_rsa and id_rsa.pub. The private key looks like this:

-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----

The public key is a lot shorter. In other scenarios, this one is used to encrypt things, while the private key is the only one that can decrypt them. The public key:

ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDVWs1VMCtg5LypQcVIZcq4jBgghEhYMm4Yf9WSNoDRPU9F7x47bQXe480+QfBVOG7gbhMWv5xd9fB3bqKQ4zU0nhyl4wlxxMrsNX66o4KHVkYrmJqfyYGxwIAqAifH92swNWFKJEPKDCkNd9k8VzhmkE3ZQ60p7kpP1jESD1uuaqRLsiZaAkAG8rZBMFrBPiqAkGQvo6IGmLW9NzpNh35ly6M9w3SrPye6nPUsA2rmjfufc/kOBbl9mgrAnCQ99zdK8BSlhbtYva1G6T1Ke+WtowVASb5QQzKLV9jKqkc0xnYy8I4ZLZtiSsdqhADQd3D33MXcZF8FV7mrU0Hv1BNZ <username here>@<hostname here>

Obviously, these are both generated just for this little explanation, and are of no value whatsoever otherwise.

There’s also another couple files that go in that ~/.ssh folder: authorized_keys and known_keys. We’re interested in the first one.

copy & paste

Ok, now we should be on the same page. Ideally, you should be at a linux computer, with your screen divided three ways between a terminal logged into your laptop, a terminal logged into your remote computer (that you want passwordless ssh on), and the words you’re reading now.

Good? Good.

On the laptop: check to see if you’ve already got ssh keys generated in the default location, if not generate them, then open the public key and copy the contents, which will be moved (in a moment) over to the other computer.

ls ~/.ssh/

If you see a file named id_rsa, you’re good. If you do not see that file, then run this command:

ssh-keygen

It will prompt you for a location - press enter to accept the default. It will ask you for a password - you don’t want one, press enter to give an empty password.

Now you have your keys. Open the public key:

cat ~/.ssh/id_rsa.pub

Copy the contents.

On the terminal of the remote computer: you have it open at your laptop, right? You’ll need to log into the root account, then open up the .ssh folder associated with the root account. Then paste the public key into the authorized_keys file (told you we’d want that later) and done.

Get into the root account, then confirm.

su
whoami

The result of the second command should be “root”. If not, back up and make sure it is. Switch to the home folder of the root account.

cd

Now open the authorized_keys file and paste in the public key.

nano /root/.ssh/authorized_keys

Save and close nano with CTRL+O and CTRL+X. You’re done! Try logging into the remote computer from the laptop with the public key you used, and it should put you right in without prompting.

Be aware, it is very dangerous to allow root ssh; no password is needed after that to modify anything. Of course, that also means it’s ideal for when you need to modify system files remotely, with a script.

the really easy alternative

Now that we’ve done the whole thing by hand, here’s the shortcut (do this from the laptop):

ssh-keygen  # if you haven't already
ssh-copy-id root@<remote computer IP address>

Done. Note that this only works if you can log in to the root account with a password. In alpine linux, you can’t. Believe me, I tried.