Troubleshooting PXE Distribution Points: Excessive File Generation in Configuration Manager

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Operating System Deployment (OSD) via Preboot Execution Environment (PXE) is a fundamental capability within Configuration Manager, enabling bare-metal deployments and task sequence execution without requiring existing operating systems. Distribution Points (DPs) play a crucial role in this process, hosting the boot images and deployment packages necessary for PXE boot. However, specific configurations can sometimes lead to unexpected behavior, such as excessive file generation on the DP server, potentially impacting system stability and performance.

This article addresses a particular issue observed in System Center 2012 Configuration Manager where a PXE-enabled Distribution Point configured to use a self-signed certificate generates a substantial number of files for each PXE request it handles. Understanding the symptoms, cause, and resolution is key to maintaining a healthy Configuration Manager environment.

Symptoms of Excessive File Generation¶

The primary symptom of this issue is the continuous creation of numerous small files within a specific system directory on the PXE-enabled Distribution Point server. This occurs whenever a device initiates a PXE boot request directed at this DP, regardless of whether a task sequence is actually deployed to that device or not.

The affected directory is typically located at C:\\ProgramData\\Microsoft\\Crypto\\RSA\\S-1-5-18. This path is part of the Windows operating system’s cryptographic service provider storage, specifically the machine’s local certificate store used by the System account (S-1-5-18 is the SID for the local system).

The consequence of this file generation is a steady and potentially rapid consumption of available free space on the DP’s system drive. Over time, this can lead to disk exhaustion, causing instability, service outages, and impacting the overall functionality of the Distribution Point and potentially other server roles hosted on the same machine. Monitoring disk space is a critical activity for Configuration Manager administrators, and noticing rapid depletion on a DP should prompt investigation into this specific directory.

Delving into the Cause¶

The root cause of this excessive file generation is directly linked to the type of certificate used by the Distribution Point. When the DP is configured to use a self-signed certificate, instead of a certificate issued by a Public Key Infrastructure (PKI), the Configuration Manager PXE service or an underlying cryptographic component appears to handle the session or authentication process inefficiently for each inbound PXE request.

Self-signed certificates are generated by Configuration Manager itself and are primarily intended for environments where a PKI is not available or practical. While they can fulfill basic authentication needs, they lack the chain of trust inherent in PKI certificates. This difference in trust model and perhaps the way the cryptographic keys associated with self-signed certificates are accessed or managed by the system’s crypto API during the frequent, short-lived connections characteristic of PXE requests, leads to the observed behavior. It’s theorized that a new cryptographic context or key handle might be instantiated and not properly cleaned up or reused for each request when a self-signed certificate is involved in the PXE process, resulting in the proliferation of small files representing these contexts or temporary key links within the machine’s crypto store.

In contrast, certificates issued by a trusted PKI are typically handled more robustly by the operating system’s cryptographic subsystem. The established trust chain and potentially different internal mechanisms for key management seem to avoid the pitfall encountered with self-signed certificates in this specific PXE scenario.

Troubleshooting Steps¶

Identifying this issue requires proactive monitoring and investigation.
1. Disk Space Monitoring: Regularly check the free disk space on your Distribution Points, particularly the system drive (C:). A sharp decline in free space over a short period on a PXE-enabled DP is a strong indicator.
2. Inspect the Crypto Directory: Navigate to C:\\ProgramData\\Microsoft\\Crypto\\RSA\\S-1-5-18 on the affected server. Observe the number of files present and the rate at which new files are being created, especially while PXE requests are actively being processed. The sheer volume of files (potentially hundreds of thousands or millions) will be immediately noticeable.
3. Review Logs: Examine relevant Configuration Manager logs on the DP, specifically smspxe.log. While this log primarily details the PXE boot process and task sequence assignment, it can confirm that the DP is actively receiving and processing PXE requests. Windows Event Logs, particularly those related to CAPI2 (Cryptographic Services), might also contain clues, although interpreting these can be complex.
4. Check Certificate Configuration: Verify the certificate configuration for the Distribution Point role in the Configuration Manager console. Confirm that it is indeed configured to use a self-signed certificate.

Once confirmed, the focus shifts to implementing the recommended resolution.

Resolution: Transitioning to a PKI Certificate¶

The definitive solution to prevent the excessive file generation caused by self-signed certificates on a PXE-enabled Distribution Point is to configure the DP role to use a certificate issued by a Public Key Infrastructure (PKI) instead of a self-signed one.

Implementing a PKI provides a scalable and secure method for certificate management across your organization. For Configuration Manager, a PKI certificate for a Distribution Point offers stronger authentication and encryption capabilities compared to a self-signed certificate. For this specific issue, using a PKI certificate fundamentally changes how the operating system and Configuration Manager components handle cryptographic operations related to PXE requests, thereby avoiding the problematic file generation.

Steps to implement a PKI certificate for a DP (Conceptual):

1. Establish or Utilize an Existing PKI: Ensure you have a functioning Certificate Authority (CA) in your environment that is trusted by the Distribution Point server and potentially by client machines (depending on your overall ConfigMgr security mode - HTTP vs. HTTPS).
2. Create a Certificate Template (if necessary): Define a certificate template on your CA specifically for Configuration Manager Distribution Points. This template should include the necessary key usage (e.g., Server Authentication) and potentially subject alternative names (SANs) if required.
3. Request and Issue the Certificate: Request a certificate from your CA for the Distribution Point server based on the appropriate template. The certificate should be stored in the server’s local computer certificate store. Ensure the certificate’s private key is marked as exportable if you might need to move it, though for a DP this is less common than for a management point.
4. Configure the Distribution Point Role: In the Configuration Manager console, modify the properties of the Distribution Point role on the affected server. Under the Communication tab (or similar depending on the specific ConfigMgr version interface), change the certificate setting from “Automatically generate a self-signed certificate” or “Use a certificate generated by Configuration Manager” to “Import certificate” or “Use a PKI client certificate”. Select the certificate you just issued from the server’s certificate store.
5. Update DP Configuration: Apply the changes. Configuration Manager will update the DP role configuration and begin using the specified PKI certificate.
6. Monitor and Verify: Monitor the C:\\ProgramData\\Microsoft\\Crypto\\RSA\\S-1-5-18 directory to confirm that new files are no longer being generated excessively when PXE requests occur. Also, verify that PXE boot and OSD task sequences continue to function correctly.

Transitioning to PKI is a recommended best practice for production Configuration Manager environments seeking enhanced security and reliability. This specific issue serves as a compelling example of how reliance on self-signed certificates can lead to unexpected and detrimental side effects.

Temporary Mitigation:

While implementing the PKI solution is the permanent fix, if you are facing immediate critical disk space issues, a temporary mitigation might involve carefully clearing the contents of the C:\\ProgramData\\Microsoft\\Crypto\\RSA\\S-1-5-18 directory after stopping relevant Configuration Manager and IIS services on the DP. However, this should be done with extreme caution and is not a supported long-term solution. It may require restarting the server and could potentially impact other applications relying on the machine’s crypto store. The best course of action is to prioritize implementing the PKI certificate.

Comparing Self-Signed and PKI Certificates for DPs¶

To further illustrate the benefits of using PKI, consider the comparison:

Feature	Self-Signed Certificate	PKI Certificate (Internal CA)
Issuance	Generated by Configuration Manager	Issued by your organization’s Certificate Authority (CA)
Trust Model	Implicitly trusted by the ConfigMgr site	Trusted via the CA’s root certificate
Security	Basic authentication	Stronger authentication and encryption
Management	Simple creation, limited central control	Centralized management via CA infrastructure
Compatibility	May encounter issues with specific features/OS versions (like this one)	Generally higher compatibility and reliability
Private Key	Managed by ConfigMgr/OS	Managed by OS crypto store, linked to CA key
Renew/Replace	Handled by ConfigMgr or manual replacement	Standard PKI renewal/replacement process

This table highlights why PKI is the preferred approach for production environments, offering not just a solution to this specific file generation problem but also overall improved security posture and manageability.

Conclusion¶

The issue of excessive file generation in the C:\\ProgramData\\Microsoft\\Crypto\\RSA\\S-1-5-18 directory on a PXE-enabled Distribution Point using a self-signed certificate is a known problem that can severely impact the server’s stability due to disk space exhaustion. The underlying cause is related to how the system handles cryptographic operations with self-signed certificates during frequent PXE requests.

The recommended and most effective resolution is to transition the Distribution Point’s certificate configuration from a self-signed certificate to one issued by a trusted Public Key Infrastructure. This not only resolves the file generation issue but also aligns with best practices for securing your Configuration Manager infrastructure. Proactive monitoring of disk space and understanding your DP’s certificate configuration are key to identifying and preventing this issue.

Have you encountered this specific issue or similar problems with certificates in Configuration Manager? Share your experiences and solutions in the comments below!