SSH login without password

You want to use Linux and OpenSSH to automate your tasks. Therefore you need an automatic login from host A / user a to Host B / user b. You don’t want to enter any passwords, because you want to call ssh from a within a shell script.

 

First log in on A as user a and generate a pair of authentication keys. Do not enter a passphrase:

Now use ssh to create a directory ~/.ssh as user b on B. (The directory may already exist, which is fine):

Finally append a’s new public key to b@B:.ssh/authorized_keys and enter b’s password one last time:

From now on you can log into B as b from A as a without password

A note from one of our readers: Depending on your version of SSH you might also have to do the following changes:

Put the public key in .ssh/authorized_keys2
Change the permissions of .ssh to 700
Change the permissions of .ssh/authorized_keys2 to 640

 

Summary

1) Run the command below on A and keep type enter while following the prompt:
ssh-keygen -t rsa

2) Create the ~/.ssh on B from A via ssh:
ssh mylogin@B mkdir -p .ssh

3) Append public key from A to B’s ~/.ssh/authorized_keys by running the command below on A:
cat ~/.ssh/id_rsa.pub | ssh mylogin@B 'cat >> .ssh/authorized_keys'

4) Verify:
ssh mylogin@B

Permission:
– ~/.ssh needs to be 700
– .ssh/authorized_key needs to be 640

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