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Log in with an SSH private key on Linux and macOS

Authored by: Brint Ohearn

This article demonstrates how to use a private key to log in to a Linux®server by using a private key with a Terminal session on macOS®. However,you can follow the same process to use a private key when using anyterminal software on Linux.

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Note: For information about using Secure Shell (SSH) private keys on Microsoft®Windows® operating systems, seeLogging in with an SSH Private Key on Windowsand Generate RSA keys with SSH by using PuTTYgen.

Prerequisites

To complete this process, you need the following software applications:

  • SSH client software that is installed on your Linux or macOS operating system by default.
  • Your favorite text editor. This example uses the vim text editor.
  • Your private key. For more information about generating a key on Linux or macOS, seeConnect to a server by using SSH on Linux or Mac OS X.

Log in with a private key

  1. Using a text editor, create a file in which to store your private key. This example usesthe file deployment_key.txt.

  2. To edit the file in vim, type the following command:

  3. After the editor starts, press i to turn on insert mode.

  4. Paste your private key, such as the one in the following image, into the file.Be sure to include the BEGIN and END lines.

  5. To save your changes, press Esc.

  6. Type :wq to write the file and return to the command line.

  7. Run the following command to change the file permissions to 600 to secure the key. You can also set them to 400.This step is required:

  8. Use the key to log in to the SSH client as shown in the following example, which loads the key in file deployment_key.txt, and logs in as user demo to IP 192.237.248.66:

  9. When you are prompted to confirm the connection, type yes and then press Enter.

  10. If your SSH key requires a password, enter it when prompted to complete the connection.

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  • On execution, we are prompted to specify a file in which to save the private key, the default being /home/user/.ssh/idrsa; here idrsa is the name of our Private Key file. You can always specify a different path and name for the Private Key file. For our demonstration, we shall use the default configuration. Step 2: Provide A Passphrase (Optional).
  • DevOps & SysAdmins: Is it harmless to use the same ssh private/public keypair from multiple computers?Helpful? Please support me on Patreon: https://www.pat.
  • Files and folders starting with a period (.ssh) are hidden by default. To find private/public key, run this commands: ls -a In your case, run this commands to find the ssh keys: cd /.ssh then: ls -a Now you should see the keys like this. Idrsa idrsa.pub.
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Ssh Private Key Example

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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. 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.

Note

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

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For more background and examples, see Detailed steps to create SSH key pairs. Adobe premiere pro free for mac.

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. If an ssh key pair already exists and the --generate-ssh-keys option is used, a new key pair will not be generated but instead the existing key pair will be used. 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:

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 myVM, myResourceGroup, UbuntuLTS, azureuser, and mysshkey.pub 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

Ssh Private Key Format

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.

Ssh Private Key

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.

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Ssh Private Key Location

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.