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:
[email protected]:~> ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/home/a/.ssh/id_rsa):
Created directory '/home/a/.ssh'.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/a/.ssh/id_rsa.
Your public key has been saved in /home/a/.ssh/id_rsa.pub.
The key fingerprint is:
ae:ff:03:74:ba:7f:66:73:3x:35:45:f5:c7:ac:57:a6 [email protected]
Now use ssh to create a directory ~/.ssh as user b on B. (The directory may already exist, which is fine):
[email protected]:~> ssh [email protected] mkdir -p .ssh
[email protected]'s password:
Finally append a’s new public key to [email protected]:.ssh/authorized_keys and enter b’s password one last time:
[email protected]:~> cat .ssh/id_rsa.pub | ssh [email protected] 'cat >> .ssh/authorized_keys'
[email protected]'s password:
From now on you can log into B as b from A as a without password
[email protected]:~> ssh [email protected]
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
- Run the command below on A and keep type enter while following the prompt:
ssh-keygen -t rsa - Create the
~/.sshon B from A via ssh:ssh [email protected] mkdir -p .ssh - Append public key from A to B’s
~/.ssh/authorized_keysby running the command below on A:cat ~/.ssh/id_rsa.pub | ssh [email protected] 'cat >> .ssh/authorized_keys' - Verify:
ssh [email protected]Permission:– ~/.ssh needs to be 700 – .ssh/authorized_key needs to be 640