Inquiries about UWF and boot speed

Question

The PC environment I am using is as follows.

• The OS is Windows 10 Enterprise 2016 LTSB version 1607.
• I only protected C drive with UWF, not D drive and I have a C# WinForms app on my D drive.
• After booting the PC, the Windows background screen does not appear and the WinForms app in the D drive runs immediately.
• Usually the WinForms app run after a black screen for 5 seconds after the Windows login screen.

The problem is that after changing the WinForms app the black screen sometimes extends up to 20 seconds.

Once the problem happened, every boot had a black screen of 20 seconds.
In this case, the problem is not resolved until I disable UWF and re-enable it.

My Winform app is on D drive, so I thought it wouldn't affect UWF. Why is this happening?

I tried excluding the path below from UWF protection, but it didn't solve the problem that the black screen stays on for 20 seconds.

• C:\Windows\Assembly
• C:\Users\User\AppData\Local

Answer 1

If you have updated the application, there is probably some .NET assembly optimization take place in the back ground. If UWF is enable, these optimizations are lost on reboot, and the optimizations happen again on each boot. When you disable UWF, the optimizations get written to the disk.

Here is some UWF write throughs for 2016 LTSB to test (Note the WinSXS and dotsvc\Policies will not work for LTSC 2019):

uwfmgr.exe file add-exclusion c:\Windows\System32\winevt\Logs
uwfmgr.exe file add-exclusion c:\Windows\WinSxS
uwfmgr.exe file add-exclusion c:\Windows\assembly
uwfmgr.exe file add-exclusion c:\Windows\dot2svc\Policies
uwfmgr.exe registry add-exclusion "HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Time Zones"
uwfmgr.exe registry add-exclusion HKLM\SYSTEM\CurrentControlSet\Control\TimeZoneInformation
uwfmgr.exe registry add-exclusion HKLM\SOFTWARE\Policies\Microsoft\Windows\WiredL2\GP_Policy
uwfmgr.exe registry add-exclusion HKLM\SYSTEM\CurrentControlSet\services\dot3svc

Are you using Shell Launcher to launch the WinForm application?

Answer 2

Thanks for the detailed reply.

My guess is the same as your opinion.
Thanks for the list of things that should be excluded from UWF protection.
Next time this happens, I'll apply the UWF protection exclusions you mentioned and see if that solves the problem.

Q. Are you using Shell Launcher to launch the WinForm application?
I set registry HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon to WinForm app instead of explorer.exe.

Answer 3

I applied all the uwf exclusions you suggested, but the black screen still keeps 20 seconds.

I'm going to investigate the Shell Launcher V1 you further mentioned. Thank you very much.

Answer 4

Hello

Thank you for your question and reaching out.

Some services and features write information to a device’s persistent volume, and expect that information to be present across device restarts. You may need to configure your write filter to allow for specific file and registry exclusions in order for these services and features to work correctly.

To add a specific file or folder to exclusions, run the following command:

Uwfmgr.exe file add-exclusion c:\temp

Below topic article shows registry and file exclusions that can help enable some common services and features to work correctly when write filters are enabled.

https://learn.microsoft.com/en-us/windows-hardware/customize/enterprise/uwfexclusions

Or it might be simpler to just turn off UWF.

My advice would be not to enable UWF for the system drive at all. If required, partition your disk to separate system and application.

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