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
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Dec 01, 2018 Where, You generate a key pair on your Linux/Unix/macOS desktop. Place the public key on RHEL 8 server. One can unlock public key using a private key stored on your desktop with the help of ssh command.
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.
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.
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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:
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:
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
.
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.
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.
OpenSSH server supports various authentication schema. The two most popular are as follows:
Steps to setup secure ssh keys:
Let us see all steps in details.
You must generate both a public and a private key pair. For example:
Where,
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 server1.cyberciti.biz and client1.cyberciti.biz names with your actual setup. Enough talk, let’s set up public key authentication. Open the Terminal and type following commands if .ssh directory does not exists:
On the computer (such as client1.cyberciti.biz), generate a key pair for the protocol.
Sample outputs:
You need to set the Key Pair location and name. I recommend you use the default location if you do not yet have another key there, for example: $HOME/.ssh/id_rsa. You will be prompted to supply a passphrase (password) for your private key. I suggest that you setup a passphrase when prompted. You should see two new files in $HOME/.ssh/ directory:
The following syntax specifies the 4096 of bits in the RSA key to creation (default 2048):$ ssh-keygen -t rsa -b 4096 -f ~/.ssh/vps-cloud.web-server.key -C 'My web-server key'
Where,
Use scp or ssh-copy-id command to copy your public key file (e.g., $HOME/.ssh/id_rsa.pub) to your account on the remote server/host (e.g., [email protected]). To do so, enter the following command on your client1.cyberciti.biz:
OR just copy the public key in remote server as authorized_keys in ~/.ssh/ directory:
On some system ssh-copy-id command may not be installed, so use the following commands (when prompted provide the password for remote user account called vivek) to install and append the public key:
The syntax is as follows for the ssh command:
Or copy a text file called foo.txt:
You will be prompted for a passphrase. To get rid of passphrase whenever you log in the remote host, try ssh-agent and ssh-add commands.
To get rid of a passphrase for the current session, add a passphrase to ssh-agent 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:
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:
Enter your private key passphrase. Now try again to log into [email protected] and you will not be prompted for a password:
One can list public key parameters of all identities with the -L option:ssh-add -L
Deleting all private keys from the ssh-agent can be done with the -D option as follows:ssh-add -D
When you log out kill the ssh agent, run:kill $SSH_AGENT_PID
You can also add something like the below to your shell startup to kill ssh-agent at logout:trap 'kill $SSH_AGENT_PID' 0
Login to your server, type:
Edit /etc/ssh/sshd_config on server1.cyberciti.biz using a text editor such as nano or vim:
Warning: Make sure you add yourself to sudoers files. Otherwise you will not able to login as root later on. See “How To Add, Delete, and Grant Sudo Privileges to Users on a FreeBSD Server” for more info.
$ sudo vim /etc/ssh/sshd_config
OR directly jump to PermitRootLogin line using a vim text editor:$ sudo vim +/PermitRootLogin /etc/ssh/sshd_config
Find PermitRootLogin and set it as follows:
Save and close the file. I am going to add a user named vivek to sudoers on Ubuntu Linux:# adduser vivek
Finally, reload/restart the sshd server, type command as per your Linux/Unix version:
To to change your passphrase type the following command:ssh-keygen -p
Just copy files to your backup server or external USB pen/hard drive:
See how to create and use an OpenSSH ssh_config file for more info.
This page explained how to set up ssh keys for authentication purposes. For more info see the following resources:
And, there you have it, ssh set up with public key based authentication for Linux or Unix-like systems.
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