Setting up OS Login

This document covers the basic steps for setting up OS Login.

OS Login lets you use Compute Engine IAM roles to grant or revoke SSH access to your Linux instances. OS Login is an alternative to managing instance access by adding and removing SSH keys in metadata. To learn more about the benefits of using this feature, see OS Login.

If you want to enable OS Login with a layer of security by using two-factor authentication, see Setting up OS Login with 2-step verification. To review all the options for managing access to your VMs, see Choosing an access method.

To configure OS Login and connect to your instances, complete the following steps:

1. Install or update the guest environment.
2. Optional: If you are an organization administrator, review Managing OS Login in an organization.
3. Enable the OS Login feature on your project or on individual instances.
4. Grant the necessary IAM roles to yourself or other principals.
5. Optional: Add custom SSH keys to user accounts for yourself or other principals. If you don't add SSH keys, Compute Engine generates SSH keys for you when you connect to instances.
6. Connect to instances.

Before you begin

• If you want to use the command-line examples in this guide, do the following:
  1. Install or update to the latest version of the gcloud command-line tool.
  2. Set a default region and zone.
• If you want to use the API examples in this guide, set up API access.
• For information about how SSH connections work in Compute Engine, including SSH key configuration and storage, see SSH connections to Linux VMs.

Limitations

• OS Login is supported in private Google Kubernetes Engine (GKE) clusters running node pool versions 1.20.5 or later.

• OS Login is not supported in public GKE clusters. Public cluster nodes continue to use metadata SSH keys when OS Login is enabled.

• Currently, Fedora CoreOS images do not support OS Login. To manage instance access to VMs created using these images, use the Fedora CoreOS ignition system.

• Windows Server and SQL Server images do not support OS Login.

Step 1: Install or update the guest environment

Your VM instance must have the latest version of the guest environment installed. Most public images already have the latest version installed. If you don't have the latest guest environment, update your guest environment.

If you have VMs that run custom images that you imported, install the guest environment on those VMs.

If you don't have the latest guest environment, update your guest environment.

Step 2: (Optional) Review managing OS Login in an organization

If you are organization admin, you can set some configurations such as enabling OS Login at the organization level. See Managing OS Login in an organization.

Step 3: Enabling or disabling OS Login

You can enable or disable OS Login by setting metadata values at the instance or project level. To set these values, you can use either the Google Cloud Console or the gcloud command-line tool.

Caution: Enabling OS Login on instances disables metadata-based SSH key configurations on those instances. Disabling OS Login restores SSH keys that you have configured in project or instance metadata.

Console

You can apply the metadata values to your projects or VMs by using one of the following options:

• Option 1: Set enable-oslogin in project-wide metadata so that it applies to all of the instances in your project.

  1. In the Google Cloud Console, go to the Metadata page.

     Go to Metadata

  2. Click Edit.

  3. Add a metadata entry, setting the key to enable-oslogin and the value to TRUE. Alternatively, set the value to FALSE to disable the feature.

  4. Click Save to apply the changes.

• Option 2: Set enable-oslogin in the instance metadata of an existing instance.

  1. In the Google Cloud Console, go to the VM instances page.

     Go to VM instances

  2. Click the name of the instance that you want to enable OS Login on.

  3. On the instance details page, click Edit.

  4. Under Custom metadata, add a metadata entry, setting the key to enable-oslogin and the value to TRUE. Alternatively, set the value to FALSE to disable OS Login on the instance.

  5. Click Save to apply the changes to the instance.

• Option 3: Set enable-oslogin in instance metadata when you create an instance.

  1. In the Cloud Console, go to the VM instances page.

     Go to VM instances

  2. Click Create instance.
  3. On the Create a new instance page, fill in the properties for your instance.
  4. In the Metadata section, add a metadata entry where the key is enable-oslogin and the value is TRUE. Alternatively, set the value to FALSE to exclude the instance from the feature.
  5. Click Create to create the instance.

gcloud

You can apply the metadata values on your projects or VMs using one of the following options:

• Option 1: Set enable-oslogin in project-wide metadata so that it applies to all of the instances in your project.

  Use the project-info add-metadata command in the gcloud command-line tool and set a metadata value where oslogin=TRUE to enable OS Login:

  gcloud compute project-info add-metadata \
      --metadata enable-oslogin=TRUE
  

  Alternatively, you can set enable-oslogin to FALSE to disable OS Login.

• Option 2: Set enable-oslogin in the metadata of an existing instance.

  Use the instances add-metadata command in the gcloud command-line tool and set oslogin=TRUE to enable OS Login. Replace VM_NAME with the name of your VM.

  gcloud compute instances add-metadata VM_NAME \
      --metadata enable-oslogin=TRUE
  

  Alternatively, you can set enable-oslogin to FALSE to exclude your instance from using OS Login.

• Option 3: Set enable-oslogin in instance metadata when you create an instance.

  Use the instances create command in the gcloud command-line tool and set oslogin=TRUE to enable OS Login. Replace VM_NAME with the name of your instance.

  gcloud compute instances create VM_NAME \
      --metadata enable-oslogin=TRUE
  

  Alternatively, you can set enable-oslogin to FALSE to exclude your instance from using OS Login.

After you enable OS Login on the instances in your project, grant users permission to connect to those instances.

Step 4: Configuring OS Login roles on user accounts

Granting OS Login IAM roles

After you enable OS Login on one or more instances in your project, those VMs accept connections only from user accounts that have the necessary IAM roles in your project or organization.

To allow OS Login access to these VMs, you need to grant the necessary roles to the user. To allow OS Login access, complete the following steps:

1. Grant one of the following instance access roles.

   • roles/compute.osLogin, which doesn't grant administrator permissions
   • roles/compute.osAdminLogin, which grants administrator permissions
   Note: If the user has the basic roles/owner or roles/editor role, or if they have roles/compute.instanceAdmin, these roles already include instance access roles with administrator permissions.

   You can grant these instance access roles at the instance level by using the gcloud compute instances add-iam-policy-binding command.

   Note: If you grant the instance access roles at the instance level, users cannot view details about your VMs or the external IP addresses for those VMs unless you provide those details directly to them. To allow these users to view VM instance details, grant additional IAM roles. For example, the roles/compute.viewer role lets users view all of the resources in your project, including VM instance details.

2. If your VM uses a service account, then each user that connects to the VM using SSH has the ability to impersonate the service account. To ensure that the impersonation follows best practices, configure each user to have the roles/iam.serviceAccountUser role on the service account. To learn how to add access for a user to a service account, see Managing service account impersonation.

   Note: VMs created by using the Google Cloud Console or the gcloud command-line tool have a service account associated by default. VMs that don't have an associated service account don't require this permission. To check if you have an associated service account, see Checking if your VM has a service account.

3. For users that are outside of your organization to access your VMs, in addition to granting an instance access role, grant the roles/compute.osLoginExternalUser role. This role must be granted at the organization level by an organization administrator. For more information, see Granting instance access to users outside of your organization.

Granting SSH access to a service account

You can use OS Login roles to allow service accounts to establish SSH connections to your instances. This is useful for the following tasks:

• If your applications require SSH access to your Compute Engine instances, you can provide that access through a service account. For more information, see Connecting apps to instances using SSH.
• For information about how to manually assume the permissions of a service account and use those permissions to execute commands on a second instance, read Manually connecting between instances as a service account.

You can grant SSH access to your service accounts by using the following process:

1. Create a service account.
2. Grant the necessary OS Login roles to your service account. Service accounts require the same roles as user accounts. To learn how to configure roles and permissions for service accounts, see Granting roles to service accounts.
3. Provide Application Default Credentials to your service account, so that it can authorize requests to the necessary APIs. Provide Application Default Credentials using one of the following options:
   • Create an instance that is associated with your service account. The instance provides Application Default Credentials to your service account.
   • Manually provide service account credentials to your app if you run your app outside of the Compute Engine environment.

After you grant SSH access to your service accounts, you can configure your apps to create SSH keys and establish SSH connections to other instances on your VPC networks. To see an example app for service account SSH, read the Connecting apps to instances using SSH tutorial.

Revoking OS Login IAM roles

To revoke user access to instances that are enabled to use OS Login, remove the user roles from that user account. For information about removing an IAM role for a user, see Granting, changing, and revoking access to resources.

When a user's access is revoked, the user will still have public SSH keys that are associated with their account, but those keys no longer function on the VM instances.

Note: Users with active SSH connections aren't disconnected and retain their sudo privileges until the next time they establish an SSH connection. Compute Engine determines a user's authentication, authorization, and sudo privileges only when a user establishes a connection to an instance.

Step 5: (Optional) Adding SSH keys to a user account

If you want connect to your VMs by using third-party tools, you need to add your SSH keys to your user account. If you connect to your instances using other options, such as the gcloud command-line tool or SSH from the browser, you can skip this step because Compute Engine automatically generates SSH keys for you.

You can associate public SSH keys with the following user account types:

• Managed user accounts that are part of an organization resource:
  • Google Workspace
  • Cloud Identity
• Consumer Google accounts, such as gmail.com accounts

You can use the gcloud command-line tool, or the OS Login API to add SSH keys to your own account. Alternatively, if you are a domain admin for an organization, you can use the Directory API to add SSH keys to the Users resource in your organization.

gcloud

The gcloud compute os-login commands are available only on Cloud SDK version 184 and later.

Use the gcloud command-line tool to associate public SSH keys with an account.

gcloud compute os-login ssh-keys add \
    --key-file=KEY_FILE_PATH \
    --ttl=EXPIRE_TIME

Replace the following:

• KEY_FILE_PATH: the path to the public SSH key on your local workstation. Ensure that the public SSH key is properly formatted. If you use PuTTYgen on Linux systems to generate your public keys, you must use the public-openssh format.
• EXPIRE_TIME: an optional flag to set an expiration time for the public SSH key. For example, you can specify 30m and the SSH key will expire after 30 minutes. This flag uses the following units:
  • s for seconds
  • m for minutes
  • h for hours
  • d for days
  • Set the value to 0 to indicate no expiration time.

OS Login API

Use the OS Login API to associate public SSH keys with an account:

POST https://oslogin.googleapis.com/v1/users/ACCOUNT_EMAIL:importSshPublicKey

{
 "key": "SSH_KEY",
 "expirationTimeUsec": "EXPIRATION_TIMESTAMP"
}

Replace the following:

• ACCOUNT_EMAIL: the email address that represents your managed user account.
• SSH_KEY: The public key that you want to apply to the account. Make sure that the public SSH key is properly formatted. If you use PuTTYgen on Linux systems to generate your public keys, you must use the public-openssh format.
• EXPIRATION_TIMESTAMP: the expiration time for the key, in microseconds since epoch.

Directory API

If you are a domain admin for an organization, you can use the Directory API reference to add SSH keys to the account of another user in your organization. For example, create a PUT request to the directory.users.update method with one or more SSH sshPublicKeys entries:

PUT https://www.googleapis.com/admin/directory/v1/users/USER_ID_KEY

{
 "sshPublicKeys": [
  {
   "key": "SSH_KEY",
   "expirationTimeUsec": "EXPIRATION_TIMESTAMP"
  },
  {
   "key": "SSH_KEY",
   "expirationTimeUsec": "EXPIRATION_TIMESTAMP"
  }
 ]
}

Replace the following:

• USER_ID_KEY: an immutable ID for the user.
• SSH_KEY: a public key that you want to apply to the account. Make sure that the public SSH key is properly formatted. If you use PuTTYgen on Linux systems to generate your public keys, you must use the public-openssh format.
• EXPIRATION_TIMESTAMP: the expiration time for a key, in microseconds since epoch.

To remove all keys from an account, specify "sshPublicKeys": null as the body, replacing USER_ID_KEY with an immutable ID for the user:

PUT https://www.googleapis.com/admin/directory/v1/users/USER_ID_KEY

{
  "sshPublicKeys": null
}

After you add your keys to your account, you can connect to instances using third-party tools and the username associated with your account. Your organization admin can change this username. Accounts that don't belong to organizations cannot change the default username.

You can find the current username for your account by running the gcloud compute os-login describe-profile command.

For example, your output might resemble the following:

name: '314159265358979323846'
posixAccounts:
- gid: '27182818'
  homeDirectory: /home/user_example_com
  ⋮
  uid: '27182818'
  username: user_example_com
⋮

Step 6: Connect to instances

When you connect to a VM, you have three main options:

• The gcloud command-line tool
• SSH from the browser
• Connecting using third-party tools

If you connect to a VM by using either the gcloud tool or SSH from the browser, Compute Engine automatically generates SSH keys and associates them with your user account.

If you connect to an instance by using a third-party tool, you need to add the public keys to your user account. The VM gets your public key from your user account and lets you connect to the instance if you provide the correct user name and matching private SSH key.

After you connect to your instance, review the expected login behaviors.

Review expected login behaviors

• On some instances using OS Login, you might receive the following error message after the connection is established:

  /usr/bin/id: cannot find name for group ID 123456789

  Ignore this error message. This error does not affect your instances.

• Cloud Identity administrators can configure POSIX information and set a username for organization members. If a username is not set by a Cloud Identity administrator, OS Login generates a default Linux username by combining the username and domain from the email address associated with the user's Google profile. This naming convention ensures uniqueness. For example, if the user email associated with the Google profile is [e-mail], then their generated username is user_example_com.

  Optionally, Google Workspace organizations can change their default to remove the domain suffix for newly generated usernames. For example, if the user email address associated with the Google profile is [e-mail], then their generated username is user. For more information, see Managing the OS Login API.

  If a user is from a separate Google Workspace organization, the generated username is prefixed with 'ext_'. For example, if [e-mail] is accessing a VM in a different organization, then their generated username is ext_user_example_com.

• When you log in to an instance by using the gcloud compute ssh command, the login message has the following format for a user user that belongs to the example.com domain:

  Using OS Login user user_example_com instead of default user user

  This message confirms that the user is logging in with an OS Login profile.

What's next

• Connect to instances.
• Learn how SSH connections to Linux VMs work on Compute Engine.
• Learn more about Compute Engine access control.
• Read about service accounts.
• Read the Connecting apps to instances using SSH tutorial to see an example app for service account SSH.
• Read about Google Cloud project access.
• Troubleshoot OS Login.