Azure Disk Encryption for Linux VMs troubleshooting guide
This guide is for IT professionals, information security analysts, and cloud administrators whose organizations use Azure Disk Encryption. This article is to help with troubleshooting disk-encryption-related problems.
Before taking any of the steps below, first ensure that the VMs you are attempting to encrypt are among the supported VM sizes and operating systems, and that you have met all the prerequisites:
Troubleshooting Linux OS disk encryption
Linux operating system (OS) disk encryption must unmount the OS drive before running it through the full disk encryption process. If it can't unmount the drive, an error message of "failed to unmount after …" is likely to occur.
This error can occur when OS disk encryption is attempted on a VM with an environment that has been changed from the supported stock gallery image. Deviations from the supported image can interfere with the extension’s ability to unmount the OS drive. Examples of deviations can include the following items:
- Customized images no longer match a supported file system or partitioning scheme.
- Large applications such as SAP, MongoDB, Apache Cassandra, and Docker aren't supported when they're installed and running in the OS before encryption. Azure Disk Encryption is unable to shut down these processes safely as required in preparation of the OS drive for disk encryption. If there are still active processes holding open file handles to the OS drive, the OS drive can't be unmounted, resulting in a failure to encrypt the OS drive.
- Custom scripts that run in close time proximity to the encryption being enabled, or if any other changes are being made on the VM during the encryption process. This conflict can happen when an Azure Resource Manager template defines multiple extensions to execute simultaneously, or when a custom script extension or other action runs simultaneously to disk encryption. Serializing and isolating such steps might resolve the issue.
- Security Enhanced Linux (SELinux) hasn't been disabled before enabling encryption, so the unmount step fails. SELinux can be reenabled after encryption is complete.
- The OS disk uses a Logical Volume Manager (LVM) scheme. Although limited LVM data disk support is available, an LVM OS disk isn't.
- Minimum memory requirements aren't met (7 GB is suggested for OS disk encryption).
- Data drives are recursively mounted under the /mnt/ directory, or each other (for example, /mnt/data1, /mnt/data2, /data3 + /data3/data4).
Update the default kernel for Ubuntu 14.04 LTS
The Ubuntu 14.04 LTS image ships with a default kernel version of 4.4. This kernel version has a known issue in which Out of Memory Killer improperly terminates the dd command during the OS encryption process. This bug has been fixed in the most recent Azure tuned Linux kernel. To avoid this error, prior to enabling encryption on the image, update to the Azure tuned kernel 4.15 or later using the following commands:
sudo apt-get update sudo apt-get install linux-azure sudo reboot
After the VM has restarted into the new kernel, the new kernel version can be confirmed using:
Update the Azure Virtual Machine Agent and extension versions
Azure Disk Encryption operations may fail on virtual machine images using unsupported versions of the Azure Virtual Machine Agent. Linux images with agent versions earlier than 2.2.38 should be updated prior to enabling encryption. For more information, see How to update the Azure Linux Agent on a VM and Minimum version support for virtual machine agents in Azure.
The correct version of the Microsoft.Azure.Security.AzureDiskEncryption or Microsoft.Azure.Security.AzureDiskEncryptionForLinux guest agent extension is also required. Extension versions are maintained and updated automatically by the platform when Azure Virtual Machine agent prerequisites are satisfied and a supported version of the virtual machine agent is used.
The Microsoft.OSTCExtensions.AzureDiskEncryptionForLinux extension has been deprecated and is no longer supported.
Unable to encrypt Linux disks
In some cases, the Linux disk encryption appears to be stuck at "OS disk encryption started" and SSH is disabled. The encryption process can take between 3-16 hours to finish on a stock gallery image. If multi-terabyte-sized data disks are added, the process might take days.
The Linux OS disk encryption sequence unmounts the OS drive temporarily. It then performs block-by-block encryption of the entire OS disk, before it remounts it in its encrypted state. Linux Disk Encryption doesn't allow for concurrent use of the VM while the encryption is in progress. The performance characteristics of the VM can make a significant difference in the time required to complete encryption. These characteristics include the size of the disk and whether the storage account is standard or premium (SSD) storage.
While the OS drive is being encrypted, the VM enters a servicing state and disables SSH to prevent any disruption to the ongoing process. To check the encryption status, use the Azure PowerShell Get-AzVmDiskEncryptionStatus command, and check the ProgressMessage field. ProgressMessage will report a series of statuses as the data and OS disks are encrypted:
PS > Get-AzVMDiskEncryptionStatus -ResourceGroupName "MyResourceGroup" -VMName "myVM" OsVolumeEncrypted : EncryptionInProgress DataVolumesEncrypted : EncryptionInProgress OsVolumeEncryptionSettings : ProgressMessage : Transitioning PS > Get-AzVMDiskEncryptionStatus -ResourceGroupName "MyResourceGroup" -VMName "myVM" OsVolumeEncrypted : EncryptionInProgress DataVolumesEncrypted : EncryptionInProgress OsVolumeEncryptionSettings : Microsoft.Azure.Management.Compute.Models.DiskEncryptionSettings ProgressMessage : Encryption succeeded for data volumes PS > Get-AzVMDiskEncryptionStatus -ResourceGroupName "MyResourceGroup" -VMName "myVM" OsVolumeEncrypted : EncryptionInProgress DataVolumesEncrypted : EncryptionInProgress OsVolumeEncryptionSettings : Microsoft.Azure.Management.Compute.Models.DiskEncryptionSettings ProgressMessage : Provisioning succeeded PS > Get-AzVMDiskEncryptionStatus -ResourceGroupName "MyResourceGroup" -VMName "myVM" OsVolumeEncrypted : EncryptionInProgress DataVolumesEncrypted : EncryptionInProgress OsVolumeEncryptionSettings : Microsoft.Azure.Management.Compute.Models.DiskEncryptionSettings ProgressMessage : OS disk encryption started
The ProgressMessage will remain in OS disk encryption started for most of the encryption process. When encryption is complete and successful, ProgressMessage will return:
PS > Get-AzVMDiskEncryptionStatus -ResourceGroupName "MyResourceGroup" -VMName "myVM" OsVolumeEncrypted : Encrypted DataVolumesEncrypted : NotMounted OsVolumeEncryptionSettings : Microsoft.Azure.Management.Compute.Models.DiskEncryptionSettings ProgressMessage : Encryption succeeded for all volumes
After this message is available, the encrypted OS drive is expected to be ready for use and the VM is ready to be used again.
If the boot information, the progress message, or an error reports that OS encryption has failed in the middle of this process, restore the VM to the snapshot or backup taken immediately before encryption. An example of a message is the "failed to unmount" error that is described in this guide.
Before reattempting encryption, reevaluate the characteristics of the VM and make sure that all of the prerequisites are satisfied.
Troubleshooting Azure Disk Encryption behind a firewall
Troubleshooting encryption status
The portal may display a disk as encrypted even after it has been unencrypted within the VM. This can occur when low-level commands are used to directly unencrypt the disk from within the VM, instead of using the higher level Azure Disk Encryption management commands. The higher level commands not only unencrypt the disk from within the VM, but outside of the VM they also update important platform level encryption settings and extension settings associated with the VM. If these are not kept in alignment, the platform will not be able to report encryption status or provision the VM properly.
To disable Azure Disk Encryption with PowerShell, use Disable-AzVMDiskEncryption followed by Remove-AzVMDiskEncryptionExtension. Running Remove-AzVMDiskEncryptionExtension before the encryption is disabled will fail.
To disable Azure Disk Encryption with CLI, use az vm encryption disable.
In this document, you learned more about some common problems in Azure Disk Encryption and how to troubleshoot those problems. For more information about this service and its capabilities, see the following articles: