Troubleshooting "Failed to Get Log Contents" Error in Azure VM Boot Diagnostics
The “Failed to get contents of the log” error within Azure Virtual Machine (VM) Boot Diagnostics can be a frustrating issue when attempting to troubleshoot virtual machines in the Azure portal. This error typically surfaces when you try to view a screenshot of your virtual machine through the Boot Diagnostics blade. This article provides a comprehensive guide to understanding the symptoms, causes, and effective workarounds to resolve this problem for both Linux and Windows VMs.
Symptoms¶
When accessing the Boot Diagnostics section of your virtual machine in the Azure portal and attempting to view the screen capture, you might encounter a failure. This failure is often indicated by an error message logged in the notification area of the Azure portal. The specific error message you are likely to see is as follows:
Failed to get contents of the log ‘<log url>’ of virtual machine ‘/subscriptions/<SUBID>/resourceGroups/<RGNAME>/providers/Microsoft.Compute/virtualMachines/<VMNAME>‘. Error message: ‘description: Failed to complete the RPC call for ‘getExtendedInfoBlob’ message: Failed to complete the RPC call for ‘getExtendedInfoBlob’ stack: ###RPC_Exception### From RPC: Microsoft_Azure_Compute -> Microsoft_Azure_Storage (getExtendedInfoBlob) (Callstack capturing is not enabled. Use ?trace=diagnostics to enable it.) ‘
This message indicates that the Azure portal is unable to retrieve the Serial Console log, which is essential for displaying the boot diagnostics information. The inability to access this log prevents you from viewing the VM screenshot and diagnosing potential boot issues.
Cause¶
Several factors can contribute to the “Failed to get contents of the log” error. Understanding these causes is crucial for effective troubleshooting. The common reasons are related to the operating system version, the VM Guest Agent, and potential issues with the VM Health Report generation.
Operating System Version¶
Virtual Machines running on older operating systems, specifically Windows Server 2008 R2 or earlier versions, are inherently unable to produce a VM Health Report. This is because the necessary components for generating this report were not implemented in these older OS versions. As a consequence, the system does not create the SerialConsole.log file in the Boot Diagnostics storage account, which leads to the error message described in the “Symptoms” section.
To verify the operating system version of your VM, you can use the winver command. Access the Command Prompt within the virtual machine and type winver, then press Enter. A window will appear displaying detailed information about the Windows version. If your VM is running Windows Server 2008 R2 or an earlier version, this could be the root cause of the error.
Outdated VM Guest Agent¶
The VM Guest Agent is a crucial component that runs inside the Azure virtual machine and is responsible for various tasks, including generating the VM Health Report. Older versions of the VM Guest Agent, specifically those earlier than version 2.7.1198.806, may not have the functionality to correctly produce this report. Similar to the OS version issue, this lack of report generation results in the absence of the SerialConsole.log file and the subsequent “Failed to get contents of the log” error.
To check the VM Guest Agent version, you need to access the virtual machine’s file system. Navigate to the C:\WindowsAzure\logs\WaAppAgent.log folder. Open the WaAppAgent.log file and search for the entry “WindowsAzureGuestAgent starting. Version”. This line will indicate the installed version of the VM Guest Agent. If the version is older than 2.7.1198.806, updating the agent is likely necessary to resolve the error.
VM Health Report Generation Failure¶
Even with a compatible operating system and a recent VM Guest Agent, the automatic generation of the VM Health Report by the agent can still fail. When this happens, the SerialConsole.log file is not created, and the error message surfaces. One common reason for this failure is the presence of unresolved Security Identifiers (SIDs) reported as members within the virtual machine’s Local Administrators group.
Unresolved SIDs can occur when user accounts or groups that were once members of the Local Administrators group are no longer valid, for example, if a domain user account has been deleted but its SID remains in the local group membership. These unresolved SIDs can disrupt the report generation process.
To investigate this possibility, examine the C:\WindowsAzure\logs\TransparentInstaller.log file within the virtual machine. This log file may contain details about issues encountered during the VM Health Report generation, including errors related to unresolved SIDs or other problems preventing the successful creation of the SerialConsole.log file.
Workaround¶
To address the “Failed to get contents of the log” error, several workarounds can be implemented depending on the identified cause.
Workaround 1: Upgrade Operating System¶
If the issue stems from running an outdated operating system like Windows Server 2008 R2 or earlier, the most direct solution is to upgrade the operating system to a more recent, supported version. Upgrading to a newer OS, such as Windows Server 2016, 2019, or 2022, will ensure compatibility with the VM Health Report generation and resolve the error related to the missing SerialConsole.log file. This is a long-term solution that not only fixes the boot diagnostics error but also brings other benefits of modern operating systems, including improved security, performance, and features.
Workaround 2: Update VM Guest Agent¶
If the cause is an outdated VM Guest Agent, updating it to the latest version or at least to version 2.7.1198.822 or later is essential. Microsoft provides a direct download link for the updated VM Guest Agent, which can be accessed through https://go.microsoft.com/fwlink/?LinkID=394789&clcid=0x409. Downloading and installing this updated agent will ensure that your VM has the necessary components to generate the VM Health Report correctly, resolving the “Failed to get contents of the log” error. After updating the agent, it is generally recommended to restart the virtual machine for the changes to take full effect.
Workaround 3: Resolve Issues with Local Administrators Group and Domain Policies¶
If the VM Health Report generation is failing due to unresolved SIDs or domain policy restrictions, you need to address these underlying issues.
First, check for and remove any unresolved SIDs from the Local Administrators group. You can use command-line tools or PowerShell to enumerate the members of the Local Administrators group and identify any SIDs that do not correspond to valid user or group accounts. Removing these orphaned SIDs can resolve the issue preventing report generation.
Second, investigate domain policies that might be locking down the Local Administrators group. Certain domain policies can restrict modifications to local groups or enforce specific membership configurations. If a domain policy is interfering with the VM Guest Agent’s ability to generate the health report, you may need to adjust the policy or create an exception for the virtual machine.
Additionally, check if the built-in Administrator account has been removed or disabled. The Transparent Installer log (C:\WindowsAzure\logs\TransparentInstaller.log) may contain an error code “0x80005004” if the built-in Administrator account is missing, which can also hinder report generation. Ensure that the built-in Administrator account is enabled and properly configured.
Workaround 4: Redeploy VM¶
In scenarios where you suspect an issue with the serial port on the host server itself, redeploying the VM can be a viable workaround. Redeploying the virtual machine essentially moves it to a different host server within the Azure infrastructure. This action can resolve underlying hardware or host-level issues that might be affecting the serial port and preventing the retrieval of boot diagnostics logs.
Warning: Redeploying a virtual machine will trigger a restart of the VM. Ensure you plan for this downtime and any potential impact on running applications or services before initiating a redeployment. To redeploy a VM, you can typically find the redeploy option within the Azure portal’s interface for managing virtual machines.
Status¶
Microsoft is actively working on a comprehensive resolution to this problem. The ongoing efforts are focused on improving the detection of scenarios where the SerialConsole.log file is not being generated. The ultimate goal is to enhance the system’s robustness and prevent the “Failed to get contents of the log” error from becoming overly disruptive during VM troubleshooting in Azure. Future updates and improvements to the Azure platform are expected to address this issue and provide a more seamless boot diagnostics experience.
If you have encountered this error, implementing the workarounds outlined above should help you regain access to the boot diagnostics information for your Azure virtual machines. If you continue to experience difficulties or have further questions, consider reaching out to Azure support for more specialized assistance.
Feel free to share your experiences or ask any questions in the comments below!
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