Centos Generate New Ssh Keys

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Now, when you're deploying servers you will be able to select which SSH keys you want to add to the newly deployed server. Remember to select the keys before the initial server deployment, otherwise you will need to log into the newly created server and add the SSH keys manually. SSH keys are only available for Linux and FreeBSD. Quick steps: Create and use an SSH public-private key pair for Linux VMs in Azure.; 4 minutes to read +4; In this article. With a secure shell (SSH) key pair, you can create virtual machines (VMs) in Azure that use SSH keys for authentication, eliminating the need for passwords to sign in. Nov 20, 2019 Setup SSH Passwordless Login on CentOS 8. SSH is a client and server protocol, and it helps us to securely access the remote system over the network through the encrypted tunnel. SSH has a built-in file transfer mechanism (SCP) to transfer files and directories over the network, and it is way more secure than FTP (File Transfer Protocol).

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With a secure shell (SSH) key pair, you can create virtual machines (VMs) in Azure that use SSH keys for authentication, eliminating the need for passwords to sign in. This article shows you how to quickly generate and use an SSH public-private key file pair for Linux VMs. You can complete these steps with the Azure Cloud Shell, a macOS or Linux host, the Windows Subsystem for Linux, and other tools that support OpenSSH.

Note

VMs created using SSH keys are by default configured with passwords disabled, which greatly increases the difficulty of brute-force guessing attacks.

For more background and examples, see Detailed steps to create SSH key pairs.

For additional ways to generate and use SSH keys on a Windows computer, see How to use SSH keys with Windows on Azure.

Supported SSH key formats

Azure currently supports SSH protocol 2 (SSH-2) RSA public-private key pairs with a minimum length of 2048 bits. Other key formats such as ED25519 and ECDSA are not supported.

Create an SSH key pair

Use the ssh-keygen command to generate SSH public and private key files. By default, these files are created in the ~/.ssh directory. You can specify a different location, and an optional password (passphrase) to access the private key file. If an SSH key pair with the same name exists in the given location, those files are overwritten.

The following command creates an SSH key pair using RSA encryption and a bit length of 4096:

If you use the Azure CLI to create your VM with the az vm create command, you can optionally generate SSH public and private key files using the --generate-ssh-keys option. The key files are stored in the ~/.ssh directory unless specified otherwise with the --ssh-dest-key-path option. The --generate-ssh-keys option will not overwrite existing key files, instead returning an error. In the following command, replace VMname and RGname with your own values:

Provide an SSH public key when deploying a VM

To create a Linux VM that uses SSH keys for authentication, specify your SSH public key when creating the VM using the Azure portal, Azure CLI, Azure Resource Manager templates, or other methods:

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If you're not familiar with the format of an SSH public key, you can display your public key with the following cat command, replacing ~/.ssh/id_rsa.pub with the path and filename of your own public key file if needed:

A typical public key value looks like this example:

If you copy and paste the contents of the public key file to use in the Azure portal or a Resource Manager template, make sure you don't copy any trailing whitespace. To copy a public key in macOS, you can pipe the public key file to pbcopy. Similarly in Linux, you can pipe the public key file to programs such as xclip.

The public key that you place on your Linux VM in Azure is by default stored in ~/.ssh/id_rsa.pub, unless you specified a different location when you created the key pair. To use the Azure CLI 2.0 to create your VM with an existing public key, specify the value and optionally the location of this public key using the az vm create command with the --ssh-key-values option. In the following command, replace VMname, RGname, and keyFile with your own values:

If you want to use multiple SSH keys with your VM, you can enter them in a space-separated list, like this --ssh-key-values sshkey-desktop.pub sshkey-laptop.pub.

SSH into your VM

With the public key deployed on your Azure VM, and the private key on your local system, SSH into your VM using the IP address or DNS name of your VM. In the following command, replace azureuser and myvm.westus.cloudapp.azure.com with the administrator user name and the fully qualified domain name (or IP address):

If you specified a passphrase when you created your key pair, enter that passphrase when prompted during the login process. The VM is added to your ~/.ssh/known_hosts file, and you won't be asked to connect again until either the public key on your Azure VM changes or the server name is removed from ~/.ssh/known_hosts.

If the VM is using the just-in-time access policy, you need to request access before you can connect to the VM. For more information about the just-in-time policy, see Manage virtual machine access using the just in time policy.

Next steps

For more information on working with SSH key pairs, see Detailed steps to create and manage SSH key pairs.
If you have difficulties with SSH connections to Azure VMs, see Troubleshoot SSH connections to an Azure Linux VM.

How do I regenerate OpenSSH sshd server host keys stored in /etc/ssh/ssh_host_* files? Can I safely regenerate ssh host keys using remote ssh session as my existing ssh connections shouldn’t be interrupted on Debian or Ubuntu Linux? How do I regenerate new ssh server keys? How to regenerate new host keys on a Debian or Ubuntu Linux?
[donotprint][/donotprint]To regenerate keys you need to delete old files and reconfigure openssh-server. It is also safe to run following commands over remote ssh based session. Your existing session shouldn’t be interrupted.

Why regenerate new ssh server keys?

Most Linux and Unix distribution create ssh keys for you during the installation of the OpenSSH server package. But it may be useful to be able re-generate new server keys from time to time. For example, when you duplicate VM (KVM or container) which contains an installed ssh package and you need to use different keys from cloned KVM VM guest/machine.

Steps to regenerate OpenSSH host keys on Linux

Let us see all steps

Step 1 – Delete old ssh host keys

Login as the root and type the following command to delete files on your SSHD server:
# /bin/rm -v /etc/ssh/ssh_host_*
Sample outputs:

Step 2 – Debian or Ubuntu Linux Regenerate OpenSSH Host Keys

Now create a new set of keys on your SSHD server, enter:
# dpkg-reconfigure openssh-server
Sample output:

You just regenerated new ssh server keys. You need to restart ssh server:
$ sudo systemctl restart ssh
OR
$ /etc/init.d/ssh restart

Step 3 – Update all ssh client(s) known_hosts files

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Finally, you need to update ~/.ssh/known_hosts files on client computers, otherwise everyone will see an error message that read as follows:

Either remove host fingerprint or update the file using vi text editor (command must be typed on client machine):
$ ssh-keygen -R remote-server-name-here
Now login using the ssh command:
$ ssh [email protected]

Conclusion

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You just regenerated OpenSSH Host Keys on a Debian or Ubuntu Linux using the dpkg-reconfigure command. For more info see the man page or this wiki page here:
$ man dpkg-reconfigure $ man sshd