Join an Ubuntu Linux virtual machine to a Microsoft Entra Domain Services managed domain

To let users sign in to virtual machines (VMs) in Azure using a single set of credentials, you can join VMs to a Microsoft Entra Domain Services managed domain. When you join a VM to a Domain Services managed domain, user accounts and credentials from the domain can be used to sign in and manage servers. Group memberships from the managed domain are also applied to let you control access to files or services on the VM.

This article shows you how to join an Ubuntu Linux VM to a managed domain.

Prerequisites

To complete this tutorial, you need the following resources and privileges:

• An active Azure subscription.
  • If you don't have an Azure subscription, create an account.
• A Microsoft Entra tenant associated with your subscription, either synchronized with an on-premises directory or a cloud-only directory.
  • If needed, create a Microsoft Entra tenant or associate an Azure subscription with your account.
• A Microsoft Entra Domain Services managed domain enabled and configured in your Microsoft Entra tenant.
  • If needed, the first tutorial creates and configures a Microsoft Entra Domain Services managed domain.
• A user account that's a part of the managed domain. Make sure the SAMAccountName attribute for the user is not autogenerated. If multiple user accounts in the Microsoft Entra tenant have the same mailNickname attribute, the SAMAccountName attribute for each user is autogenerated. For more information, see How objects and credentials are synchronized in a Microsoft Entra Domain Services managed domain.
• Unique Linux VM names that are a maximum of 15 characters to avoid truncated names that might cause conflicts in Active Directory.

Create and connect to an Ubuntu Linux VM

If you have an existing Ubuntu Linux VM in Azure, connect to it using SSH, then continue on to the next step to start configuring the VM.

If you need to create an Ubuntu Linux VM, or want to create a test VM for use with this article, you can use one of the following methods:

• Microsoft Entra admin center
• Azure CLI
• Azure PowerShell

When you create the VM, pay attention to the virtual network settings to make sure that the VM can communicate with the managed domain:

• Deploy the VM into the same, or a peered, virtual network in which you have enabled Microsoft Entra Domain Services.
• Deploy the VM into a different subnet than your Microsoft Entra Domain Services managed domain.

Once the VM is deployed, follow the steps to connect to the VM using SSH.

Configure the hosts file

To make sure that the VM host name is correctly configured for the managed domain, edit the /etc/hosts file and set the hostname:

sudo vi /etc/hosts

In the hosts file, update the localhost address. In the following example:

• aaddscontoso.com is the DNS domain name of your managed domain.
• ubuntu is the hostname of your Ubuntu VM that you're joining to the managed domain.

Update these names with your own values:

127.0.0.1 ubuntu.aaddscontoso.com ubuntu

When done, save and exit the hosts file using the :wq command of the editor.

Install required packages

The VM needs some additional packages to join the VM to the managed domain. To install and configure these packages, update and install the domain-join tools using apt-get

During the Kerberos installation, the krb5-user package prompts for the realm name in ALL UPPERCASE. For example, if the name of your managed domain is aaddscontoso.com, enter AADDSCONTOSO.COM as the realm. The installation writes the [realm] and [domain_realm] sections in /etc/krb5.conf configuration file. Make sure that you specify the realm an ALL UPPERCASE:

sudo apt-get update
sudo apt-get install krb5-user samba sssd sssd-tools libnss-sss libpam-sss ntp ntpdate realmd adcli

Configure Network Time Protocol (NTP)

For domain communication to work correctly, the date and time of your Ubuntu VM must synchronize with the managed domain. Add your managed domain's NTP hostname to the /etc/ntp.conf file.

1. Open the ntp.conf file with an editor:

   sudo vi /etc/ntp.conf
   

2. In the ntp.conf file, create a line to add your managed domain's DNS name. In the following example, an entry for aaddscontoso.com is added. Use your own DNS name:

   server aaddscontoso.com
   

   When done, save and exit the ntp.conf file using the :wq command of the editor.

3. To make sure that the VM is synchronized with the managed domain, the following steps are needed:

   • Stop the NTP server
   • Update the date and time from the managed domain
   • Start the NTP service

   Run the following commands to complete these steps. Use your own DNS name with the ntpdate command:

   sudo systemctl stop ntp
   sudo ntpdate aaddscontoso.com
   sudo systemctl start ntp
   

Join VM to the managed domain

Now that the required packages are installed on the VM and NTP is configured, join the VM to the managed domain.

1. Use the realm discover command to discover the managed domain. The following example discovers the realm AADDSCONTOSO.COM. Specify your own managed domain name in ALL UPPERCASE:

   sudo realm discover AADDSCONTOSO.COM
   

   If the realm discover command can't find your managed domain, review the following troubleshooting steps:

   • Make sure that the domain is reachable from the VM. Try ping aaddscontoso.com to see if a positive reply is returned.
   • Check that the VM is deployed to the same, or a peered, virtual network in which the managed domain is available.
   • Confirm that the DNS server settings for the virtual network have been updated to point to the domain controllers of the managed domain.

2. Now initialize Kerberos using the kinit command. Specify a user that's a part of the managed domain. If needed, add a user account to a group in Microsoft Entra ID.

   Again, the managed domain name must be entered in ALL UPPERCASE. In the following example, the account named contosoadmin@aaddscontoso.com is used to initialize Kerberos. Enter your own user account that's a part of the managed domain:

   sudo kinit -V contosoadmin@AADDSCONTOSO.COM
   

3. Finally, join the VM to the managed domain using the realm join command. Use the same user account that's a part of the managed domain that you specified in the previous kinit command, such as contosoadmin@AADDSCONTOSO.COM:

   sudo realm join --verbose AADDSCONTOSO.COM -U 'contosoadmin@AADDSCONTOSO.COM' --install=/
   

It takes a few moments to join the VM to the managed domain. The following example output shows the VM has successfully joined to the managed domain:

Successfully enrolled machine in realm

If your VM can't successfully complete the domain-join process, make sure that the VM's network security group allows outbound Kerberos traffic on TCP + UDP port 464 to the virtual network subnet for your managed domain.

If you received the error Unspecified GSS failure. Minor code may provide more information (Server not found in Kerberos database), open the file /etc/krb5.conf and add the following code in [libdefaults] section and try again:

rdns=false

Update the SSSD configuration

One of the packages installed in a previous step was for System Security Services Daemon (SSSD). When a user tries to sign in to a VM using domain credentials, SSSD relays the request to an authentication provider. In this scenario, SSSD uses Domain Services to authenticate the request.

1. Open the sssd.conf file with an editor:

   sudo vi /etc/sssd/sssd.conf
   

2. Comment out the line for use_fully_qualified_names as follows:

   # use_fully_qualified_names = True
   

   When done, save and exit the sssd.conf file using the :wq command of the editor.

3. To apply the change, restart the SSSD service:

   sudo systemctl restart sssd
   

Configure user account and group settings

With the VM joined to the managed domain and configured for authentication, there are a few user configuration options to complete. These configuration changes include allowing password-based authentication, and automatically creating home directories on the local VM when domain users first sign in.

Allow password authentication for SSH

By default, users can only sign in to a VM using SSH public key-based authentication. Password-based authentication fails. When you join the VM to a managed domain, those domain accounts need to use password-based authentication. Update the SSH configuration to allow password-based authentication as follows.

1. Open the sshd_conf file with an editor:

   sudo vi /etc/ssh/sshd_config
   

2. Update the line for PasswordAuthentication to yes:

   PasswordAuthentication yes
   

   When done, save and exit the sshd_conf file using the :wq command of the editor.

3. To apply the changes and let users sign in using a password, restart the SSH service:

   sudo systemctl restart ssh
   

Configure automatic home directory creation

To enable automatic creation of the home directory when a user first signs in, complete the following steps:

1. Open the /etc/pam.d/common-session file in an editor:

   sudo vi /etc/pam.d/common-session
   

2. Add the following line in this file below the line session optional pam_sss.so:

   session required pam_mkhomedir.so skel=/etc/skel/ umask=0077
   

   When done, save and exit the common-session file using the :wq command of the editor.

Grant the 'AAD DC Administrators' group sudo privileges

To grant members of the AAD DC Administrators group administrative privileges on the Ubuntu VM, you add an entry to the /etc/sudoers. Once added, members of the AAD DC Administrators group can use the sudo command on the Ubuntu VM.

1. Open the sudoers file for editing:

   sudo visudo
   

2. Add the following entry to the end of /etc/sudoers file:

   # Add 'AAD DC Administrators' group members as admins.
   %AAD\ DC\ Administrators ALL=(ALL) NOPASSWD:ALL
   

   When done, save and exit the editor using the Ctrl-X command.

Sign in to the VM using a domain account

To verify that the VM has been successfully joined to the managed domain, start a new SSH connection using a domain user account. Confirm that a home directory has been created, and that group membership from the domain is applied.

1. Create a new SSH connection from your console. Use a domain account that belongs to the managed domain using the ssh -l command, such as contosoadmin@aaddscontoso.com and then enter the address of your VM, such as ubuntu.aaddscontoso.com. If you use the Azure Cloud Shell, use the public IP address of the VM rather than the internal DNS name.

   sudo ssh -l contosoadmin@AADDSCONTOSO.com ubuntu.aaddscontoso.com
   

2. When you've successfully connected to the VM, verify that the home directory was initialized correctly:

   sudo pwd
   

   You should be in the /home directory with your own directory that matches the user account.

3. Now check that the group memberships are being resolved correctly:

   sudo id
   

   You should see your group memberships from the managed domain.

4. If you signed in to the VM as a member of the AAD DC Administrators group, check that you can correctly use the sudo command:

   sudo apt-get update
   

Next steps

If you have problems connecting the VM to the managed domain or signing in with a domain account, see Troubleshooting domain join issues.