Windows Startup Failure and the NUL System Device
Verify a reported NUL-device failure, distinguish missing files from service or permission problems, and choose the matching repair procedure.
Verify a reported NUL-device failure, distinguish missing files from service or permission problems, and choose the matching repair procedure.
NUL is a built-in Windows device. If it is unavailable, the app and its local service may fail to start. Follow this guide when the installer or an error explicitly reports an unavailable NUL device or Unable to open nul device.
No response on launch, “standard mode failed”, an unknown error or read ENOTCONN can also have other causes. Those symptoms alone do not prove that NUL is missing.
1. Check device access
Open PowerShell or Terminal and run:
cmd /c "echo test > nul"
- No error and a new prompt: this write check passed. If the app still fails, keep its error message and investigate other causes; do not modify the Null service.
- “The system cannot find the file specified”: continue with the file and service checks.
- “Access denied” or another error: ask an administrator to investigate permissions or policy rather than assuming a file was deleted.
The app can exit before displaying its own diagnostic window, so the absence of a dialog does not prove the device is healthy.
2. Check the driver and service
Run these separately in PowerShell:
Get-Item "$env:SystemRoot\System32\drivers\null.sys" | Select-Object Length
sc.exe query Null
sc.exe qc Null
Use sc.exe, not the PowerShell alias sc. File existence, size and service state are different checks. A small file is not proof of integrity, and an unusually large file alone does not prove malicious replacement. Ask support or your administrator to confirm ambiguous results.
3. Repair a confirmed missing or disabled service
Run the following modification commands only in an administrator terminal and only after confirming the driver is usable.
If the service query reports error 1060, meaning the service does not exist:
sc.exe create Null type= kernel start= system error= normal binPath= System32\drivers\Null.SYS group= Base
sc.exe start Null
Keep the spaces after the equals signs. If the service already exists, inspect sc.exe qc Null. Only if it is disabled, use:
sc.exe config Null start= system
sc.exe start Null
“Service already exists” does not mean “service disabled”. If it is running or fails to start, retain the error code and ask an administrator to investigate.
4. Restore a missing driver file
In an administrator terminal, run the Windows system-file check:
sfc /scannow
Wait for completion and follow its result. If some files cannot be repaired, an administrator may need a trusted repair source matching the Windows version. That result alone does not prove the component backup was deleted.
After restoring the file, recheck the service. Create or reconfigure it only if the corresponding condition is confirmed, then restart when Windows requests it.
5. Investigate a suspicious file
Do not overwrite a system driver based only on its size. Have an administrator or support verify the Windows version, source and signature. Use official Microsoft installation media or a trusted matching repair source, not a third-party system-file download site.
The app provides checks and instructions; it does not automatically download or register system drivers. A shortcut launch option cannot restore a missing NUL device.
6. Verify recovery
Run cmd /c "echo test > nul" again, confirm it succeeds, then open the app and enter the search workspace. A successful device check does not diagnose any separate error that remains.
If system components repeatedly fail or several applications develop problems, ask an administrator to review system integrity and any system-cleanup tools.