Azure Disk Encryption for Linux VMs

Applies to: ✔️ Linux VMs ✔️ Flexible scale sets

Azure Disk Encryption helps protect and safeguard your data to meet your organizational security and compliance commitments. It uses the DM-Crypt feature of Linux to provide volume encryption for the OS and data disks of Azure virtual machines (VMs), and is integrated with Azure Key Vault to help you control and manage the disk encryption keys and secrets.

Azure Disk Encryption is zone resilient, the same way as Virtual Machines. For details, see Azure Services that support Availability Zones.

If you use Microsoft Defender for Cloud, you're alerted if you have VMs that aren't encrypted. The alerts show as High Severity and the recommendation is to encrypt these VMs.

You can learn the fundamentals of Azure Disk Encryption for Linux in just a few minutes with the Create and encrypt a Linux VM with Azure CLI quickstart or the Create and encrypt a Linux VM with Azure PowerShell quickstart.

Supported VMs and operating systems

Supported VMs

Linux VMs are available in a range of sizes. Azure Disk Encryption is supported on Generation 1 and Generation 2 VMs. Azure Disk Encryption is also available for VMs with premium storage.

See Azure VM sizes with no local temporary disk.

Azure Disk Encryption is also not available on Basic, A-series VMs, or on virtual machines that do not meet these minimum memory requirements:

Memory requirements

Once the OS disk encryption process is complete on Linux virtual machines, the VM can be configured to run with less memory.

For more exceptions, see Azure Disk Encryption: Restrictions.

Supported operating systems

Azure Disk Encryption is supported on a subset of the Azure-endorsed Linux distributions, which is itself a subset of all Linux server possible distributions.

Linux server distributions that are not endorsed by Azure do not support Azure Disk Encryption; of those that are endorsed, only the following distributions and versions support Azure Disk Encryption:

* For image versions greater than or equal to May 2023.

Additional VM requirements

Azure Disk Encryption requires the dm-crypt and vfat modules to be present on the system. Removing or disabling vfat from the default image will prevent the system from reading the key volume and obtaining the key needed to unlock the disks on subsequent reboots. System hardening steps that remove the vfat module from the system or enforce expanding the OS mountpoints/folders on data drives are not compatible with Azure Disk Encryption.

Before enabling encryption, the data disks to be encrypted must be properly listed in /etc/fstab. Use the "nofail" option when creating entries, and choose a persistent block device name (as device names in the "/dev/sdX" format may not be associated with the same disk across reboots, particularly after encryption; for more detail on this behavior, see: Troubleshoot Linux VM device name changes).

Make sure the /etc/fstab settings are configured properly for mounting. To configure these settings, run the mount -a command or reboot the VM and trigger the remount that way. Once that is complete, check the output of the lsblk command to verify that the drive is still mounted.

• If the /etc/fstab file doesn't mount the drive properly before enabling encryption, Azure Disk Encryption won't be able to mount it properly.
• The Azure Disk Encryption process will move the mount information out of /etc/fstab and into its own configuration file as part of the encryption process. Don't be alarmed to see the entry missing from /etc/fstab after data drive encryption completes.
• Before starting encryption, be sure to stop all services and processes that could be writing to mounted data disks and disable them, so that they do not restart automatically after a reboot. These could keep files open on these partitions, preventing the encryption procedure to remount them, causing failure of the encryption.
• After reboot, it will take time for the Azure Disk Encryption process to mount the newly encrypted disks. They won't be immediately available after a reboot. The process needs time to start, unlock, and then mount the encrypted drives before being available for other processes to access. This process may take more than a minute after reboot depending on the system characteristics.

Here is an example of the commands used to mount the data disks and create the necessary /etc/fstab entries:

sudo UUID0="$(blkid -s UUID -o value /dev/sda1)"
sudo UUID1="$(blkid -s UUID -o value /dev/sda2)"
sudo mkdir /data0
sudo mkdir /data1
sudo echo "UUID=$UUID0 /data0 ext4 defaults,nofail 0 0" >>/etc/fstab
sudo echo "UUID=$UUID1 /data1 ext4 defaults,nofail 0 0" >>/etc/fstab
sudo mount -a

Networking requirements

To enable the Azure Disk Encryption feature, the Linux VMs must meet the following network endpoint configuration requirements:

• To get a token to connect to your key vault, the Linux VM must be able to connect to a Microsoft Entra endpoint, [login.microsoftonline.com].
• To write the encryption keys to your key vault, the Linux VM must be able to connect to the key vault endpoint.
• The Linux VM must be able to connect to an Azure storage endpoint that hosts the Azure extension repository and an Azure storage account that hosts the VHD files.
• If your security policy limits access from Azure VMs to the Internet, you can resolve the preceding URI and configure a specific rule to allow outbound connectivity to the IPs. For more information, see Azure Key Vault behind a firewall.

Encryption key storage requirements

Azure Disk Encryption requires an Azure Key Vault to control and manage disk encryption keys and secrets. Your key vault and VMs must reside in the same Azure region and subscription.

For details, see Creating and configuring a key vault for Azure Disk Encryption.

Terminology

The following table defines some of the common terms used in Azure disk encryption documentation:

Next steps

• Quickstart - Create and encrypt a Linux VM with Azure CLI
• Quickstart - Create and encrypt a Linux VM with Azure PowerShell
• Azure Disk Encryption scenarios on Linux VMs
• Azure Disk Encryption prerequisites CLI script
• Azure Disk Encryption prerequisites PowerShell script
• Creating and configuring a key vault for Azure Disk Encryption