Typically, SSH keys is more secure and convenient than traditional password authentication. In this article, I’m going to show how to setup SSH key-based login on any linux server such as CentOS, Ubuntu. Let’s get started:

Table of Contents

1. Generate SSH Key
2. Copy Public Key to Server
3. Login Using Key

Generate SSH Key

We want to login to our server from our PC without entering password. Let’s do it. From your PC, run this commad:

ssh-keygen -t rsa -b 4096 -C "[email protected]"

It will ask you to provide a file name.

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

We want to store in default file. Just hit ENTER button.

Then it’ll ask you to provide a passphrase. You can skip it. Just press ENTER button.

Enter passphrase (empty for no passphrase):

To verify your new SSH key pair is generated, run this command:

ls ~/.ssh/id_*

Output will look like:

/home/username/.ssh/id_rsa /home/username/.ssh/id_rsa.pub

We’ve successfully generated SSH key in our PC.

Copy Public Key to Server

We need to add our newly generated key to our server. We can copy with ssh-copy-id utility. Run this command to copy:

ssh-copy-id remote_username@server_ip_address

If ssh-copy-id is not available on your computer, you can copy SSH key to server using this command:

cat ~/.ssh/id_rsa.pub | ssh remote_username@server_ip_address "mkdir -p ~/.ssh && chmod 700 ~/.ssh && cat >> ~/.ssh/authorized_keys && chmod 600 ~/.ssh/authorized_keys"

Then we need to enter the remote user password to login to server.

remote_username@server_ip_address's password:

After authenticating, the local file (~/.ssh/id_rsa.pub) will be copied to the remote user’s ~/.ssh/authorized_keys file.

Output:

Number of key(s) added: 1

Now try logging into the machine, with:   "ssh 'username@server_ip_address'"
and check to make sure that only the key(s) you wanted were added.

Login Using Key

Now just run this command to login to server:

ssh remote_username@server_ip_address

That’s all. Thanks for reading.