2 min read

HOWTO: Passwordless ssh logins

UPDATE2: Recently, while building a proof of concept computer cluster, I came across a much simpler way to do this.¬† If you have ssh-keygen and ssh-copy-id installed, it’s a two step process

First, create a password-less ssh rsa key:

ssh-keygen -b 2048 -f ~/.ssh/id_rsa -P ''

Second, copy the key to your remote host:

ssh-copy-id user@remote.host

Note, if you’re using a different port, or want to call out any other ssh features, put it in single quotes like this:

ssh-copy-id '-p 2222 user@remote.host'

And that’s it, easy cheesy. Might as well test it to make sure it worked:

ssh user@remote.host

It should drop you to a prompt on the remote box without asking for a password.

UPDATE: Apparently this has changed slightly, instead of writing to autorized_keys, you should use authorized_keys2 so any updates to the core OpenSSH won’t mess up your ‘local’ keyfile (verus the system one). ¬†Here are the correct (and more complete) directions:

ssh-keygen -t rsa

You shouldn’t have a key stored there yet, but if you do it will prompt you now; make sure you overwrite it.

Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 

We’re not using passphrases so logins can be automated, this should only be done for scripts or applications that need this functionality, using a non-privileged user - it’s not for logging into servers lazily! Don’t make me come down there!

Now, replace REMOTE_SERVER with the hostname or IP that you’re going to call when you SSH to it, and copy the key over to the server:

cat ~/.ssh/id_rsa.pub | ssh REMOTE_SERVER 'cat - >> ~/.ssh/authorized_keys2'

Set the permissions to a sane level:

ssh REMOTE_SERVER 'chmod 700 .ssh'

Lastly, give it a go to see if it worked:


It should drop you to a prompt on the remote box without asking for a password.

My old, now deprecated, method:

ssh-keygen -t rsa
cat ~/.ssh/id_rsa.pub | ssh REMOTE_SERVER 'cat - >> ~/.ssh/authorized_keys'
ssh REMOTE_SERVER 'chmod 700 .ssh'