How to use SSH keys based authentication to login in Linux Server Print

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To set up a password-less SSH login in Linux all you need to do is to generate a public authentication key and append it to the remote hosts ~/.ssh/authorized_keys file.

The following steps will describe the process for configuring password-less SSH login:

  1. Check for existing SSH key pair

Before generating a new SSH key pair first check if you already have an SSH key on your client machine because you don’t want to overwrite your existing keys.

Run the following ls command to see if existing SSH keys are present:

  • ls -al ~/.ssh/id_*.pub

If there are existing keys, you can either use those and skip the next step or backup up the old keys and generate a new one.

If you see No such file or directory or no matches found it means that you do not have an SSH key and you can proceed with the next step and generate a new one.

  1. Generate a new SSH key pair

The following command will generate a new 4096 bits SSH key pair with your email address as a comment:

Press Enter to accept the default file location and file name:

Enter file in which to save the key (/home/yourusername/.ssh/id_rsa):

Next, the ssh-keygen tool will ask you to type a secure passphrase. Whether you want to use passphrase it’s up to you, if you choose to use passphrase you will get an extra layer of security. In most cases, developers and system administrators use SSH without a passphrase because they are useful for fully automated processes. If you don’t want to use a passphrase just press Enter.

Enter passphrase (empty for no passphrase):

The whole interaction looks like this

To be sure that the SSH keys are generated you can list your new private and public keys with:

~$ ls ~/.ssh/id_*

/home/yourusername/.ssh/id_rsa /home/yourusername/.ssh/

  1. Copy the public key

Now that you have generated an SSH key pair, in order to be able to login to your server without a password you need to copy the public key to the server you want to manage.

The easiest way to copy your public key to your server is to use a command called ssh-copy-id. On your local machine terminal type:

You will be prompted to enter the remote_username password:  [email protected]_ip_address's password:

Once the user is authenticated, the public key will be appended to the remote user authorized_keys file and connection will be closed.

If by some reason the ssh-copy-id utility is not available on your local computer you can use the following command to copy the public key:

  • cat ~/.ssh/ | ssh [email protected]_ip_address "mkdir -p ~/.ssh && chmod 700 ~/.ssh && cat >> ~/.ssh/authorized_keys && chmod 600 ~/.ssh/authorized_keys"
  1. Login to your server using SSH keys

After completing the steps above you should be able log in to the remote server without being prompted for a password.

To test it just try to login to your server via SSH:

ssh [email protected]_ip_address

If everything went well, you will be logged in immediately.

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