Ubuntu Generate Ssh Key Rsa

SSH, the secure shell, is often used to access remote Linux systems. But its authentication mechanism, where a private local key is paired with a public remote key, is used to secure all kinds of online services, from GitHub and Launchpad to Linux running on Microsoft’s Azure cloud.

Step One: Creation of the RSA Key Pair. The first step in the installation process is to create the key pair on the client machine, which would, more often than not, be your own system. Users need to use the following command: ssh-keygen -o -b 4096 -t rsa. The above command kicks off the SSH Key installation process for users.

Generating these keys from Linux is easy, and thanks to Ubuntu on Windows, you can follow the same process from Windows 10. But even without Ubuntu, SSH keys can also be generated with the free and open source Windows application, PuTTy

Over the following few steps, we’ll guide you through the process of generating SSH keys using both Ubuntu on Windows and PuTTY.


All you need is a PC running Windows 10 and either of the following installed:

  • The puttygen.exe executable from PuTTY

If you don’t already have Ubuntu on Windows, take a look at our Install Ubuntu on Windows 10 tutorial.

Ubuntu Generate Ssh Key RsaI am a new Ubuntu 18.04 LTS user and I would like to setup ssh public key authentication. How do I set up ssh keys based authentication on Ubuntu Linux 18.04 LTS server? How do I set up SSH keys on an Ubuntu Linux 18.04 LTS server? In Ubuntu 18.04 LTS, how do I set up public key authentication?
Introduction: OpenSSH is a free and open source client/server technology for secure remote login. It is an implementation of the SSH protocol. OpenSSH divided into sshd (server) and various client tools such as sftp, scp, ssh and more. One can do remote login with OpenSSH either using password or combination of private and public keys named as public key based authentication. It is an alternative security method for user passwords. This method is recommended on a VPS, cloud, dedicated or even home-based server or laptop. This page shows how to set up SSH keys on Ubuntu 18.04 LTS server.

Ubuntu 18.04 Setup SSH Public Key Authentication

The procedure to set up secure ssh keys on Ubuntu 18.04:

  1. Create the key pair using ssh-keygen command.
  2. Copy and install the public key using ssh-copy-id command.
  3. Add yourself to sudo admin account on Ubuntu 18.04 server.
  4. Disable the password login for root account on Ubuntu 18.04.

Sample set up for SSH Keys on Ubuntu 18.04


  • – You store your public key on the remote hosts and you have an accounts on this Ubuntu Linux 18.04 LTS server.
  • Linux/macbook laptop – Your private key stays on the desktop/laptop/computer (or local server) you use to connect to server. Do not share or give your private file to anyone.

In public key based method you can log into remote hosts and server, and transfer files to them, without using your account passwords. Feel free to replace and client names with your actual setup. Enough talk, let’s set up public key authentication on Ubuntu Linux 18.04 LTS.

How to create the RSA/ed25519 key pair on your local desktop/laptop

Open the Terminal and type following commands if .ssh directory does not exists:
$ mkdir -p $HOME/.ssh
$ chmod 0700 $HOME/.ssh

Next generate a key pair for the protocol, run:
$ ssh-keygen
$ ssh-keygen -t rsa 4096 -C 'My key for Linode server'
These days ED25519 keys are favored over RSA keys when backward compatibility is not needed:
$ ssh-keygen -t ed25519 -C 'My key for Linux server # 42'

How to install the public key in Ubuntu 18.04 remote server

The syntax is as follows:
ssh-copy-id [email protected]
ssh-copy-id -i ~/.ssh/file.pub [email protected]

For example:
## for RSA KEY ##
ssh-copy-id -i $HOME/.ssh/id_rsa.pub [email protected]
## for ED25519 KEY ##
ssh-copy-id -i $HOME/.ssh/id_ed25519.pub [email protected]
## install SSH KEY for root user ##
ssh-copy-id -i $HOME/.ssh/id_ed25519.pub [email protected]

I am going to install ssh key for a user named vivek (type command on your laptop/desktop where you generated RSA/ed25519 keys):
$ ssh-copy-id -i ~/.ssh/id_ed25519.pub [email protected]

Test it

Now try logging into the Ubuntu 18.04 LTS server, with ssh command from your client computer/laptop using ssh keys:
$ ssh [email protected]
$ ssh [email protected]

What are ssh-agent and ssh-add, and how do I use them on Ubuntu 18.04?

To get rid of a passphrase for the current session, add a passphrase to ssh-agent (see ssh-agent command for more info) and you will not be prompted for it when using ssh or scp/sftp/rsync to connect to hosts with your public key. The syntax is as follows:
$ eval $(ssh-agent)
Type the ssh-add command to prompt the user for a private key passphrase and adds it to the list maintained by ssh-agent command:
$ ssh-add
Enter your private key passphrase. Now try again to log into [email protected] and you will NOT be prompted for a password:
$ ssh [email protected]

How to disable the password based login on a Ubuntu 18.04 server

Ubuntu Generate Ssh Key Rsa File

Login to your server, type:
## client commands ##
$ eval $(ssh-agent)
$ ssh-add
$ ssh [email protected]

Now login as root user:
$ sudo -i
$ su -i
Edit sshd_config file:
# vim /etc/ssh/sshd_config
# nano /etc/ssh/sshd_config
Find PermitRootLogin and set it as follows:
PermitRootLogin no
Save and close the file. I am going to add a user named vivek to sudoers group on Ubuntu 18.04 server so that we can run sysadmin tasks:
# adduser vivek sudo
Restart/reload the sshd service:
# systemctl reload ssh
You can exit from all session and test it as follows:
$ ssh [email protected]
## become root on server for sysadmin task ##
$ sudo -i

How do I add or replace a passphrase for an existing private key?

Generate Ssh Key Ubuntu

To to change your SSH passphrase type the following command:
$ ssh-keygen -p

How do I backup my existing private/public SSH keys

Just copy files to your backup server or external USB pen/hard drive:

How do I protect my ssh keys?

  1. Always use a strong passphrase.
  2. Do not share your private keys anywhere online or store in insecure cloud storage or gitlab/github servers.
  3. Restrict privileges of the account.

Tip: Create and setup an OpenSSH config file to create shortcuts for servers

See how to create and use an OpenSSH ssh_config file for more info.

How do I secure my OpenSSH server?

See “OpenSSH Server Best Security Practices” for more info.

Ubuntu Generate Ssh Key Rsa Key


You learned how to create and install ssh keys for SSH key-based authentication for Ubuntu Linux 18.04 LTS server. See OpenSSH server documents here and here for more info.

Create Rsa Key Ubuntu