System.IO.Tests fails with "Unexpected error code getting attributes 64 from path \\LOCALHOST"

[jkotas]

Build Information

Build: https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_build/results?buildId=1181840
Build error leg or test failing: System.IO.FileSystem.Tests.WorkItemExecution
Pull request: #119878

Error Message

Fill the error message using step by step known issues guidance.

{
  "ErrorMessage": "Unexpected error code getting attributes 64 from path \\\\LOCALHOST",
  "ErrorPattern": "",
  "BuildRetry": false,
  "ExcludeConsoleLog": false
}

Known issue validation

Build: 🔎 https://dev.azure.com/dnceng-public/public/_build/results?buildId=1181840
Error message validated: [Unexpected error code getting attributes 64 from path \LOCALHOST]
Result validation: ❌ Known issue did not match with the provided build.
Validation performed at: 10/22/2025 2:11:40 PM UTC

Known issue validation

Build: 🔎 https://dev.azure.com/dnceng-public/public/_build/results?buildId=1181840
Error message validated: [Unexpected error code getting attributes 64 from path \\LOCALHOST]
Result validation: ✅ Known issue matched with the provided build.
Validation performed at: 10/22/2025 2:17:17 PM UTC

Report

Build	Definition	Test	Pull Request
1190130	dotnet/runtime	System.IO.FileSystem.Tests.WorkItemExecution
1189705	dotnet/runtime	System.IO.FileSystem.Tests.WorkItemExecution
1189162	dotnet/runtime	System.IO.FileSystem.Tests.WorkItemExecution
1188795	dotnet/runtime	System.IO.FileSystem.Tests.WorkItemExecution
1188689	dotnet/runtime	System.IO.FileSystem.Tests.WorkItemExecution
1188687	dotnet/runtime	System.IO.FileSystem.Tests.WorkItemExecution	#121167
1188210	dotnet/runtime	System.IO.FileSystem.Tests.WorkItemExecution
1187788	dotnet/runtime	System.IO.FileSystem.Tests.WorkItemExecution
1187342	dotnet/runtime	System.IO.FileSystem.Tests.WorkItemExecution
1186385	dotnet/runtime	System.IO.FileSystem.Tests.WorkItemExecution
1186061	dotnet/runtime	System.IO.FileSystem.Tests.WorkItemExecution
1185668	dotnet/runtime	System.IO.FileSystem.Tests.WorkItemExecution
1185098	dotnet/runtime	System.IO.FileSystem.Tests.WorkItemExecution
1184245	dotnet/runtime	System.IO.FileSystem.Tests.WorkItemExecution
1183074	dotnet/runtime	System.IO.FileSystem.Tests.WorkItemExecution
1182479	dotnet/runtime	System.IO.FileSystem.Tests.WorkItemExecution
1182408	dotnet/runtime	System.IO.FileSystem.Tests.WorkItemExecution	#119878
1181840	dotnet/runtime	System.IO.FileSystem.Tests.WorkItemExecution	#119878

Summary

24-Hour Hit Count	7-Day Hit Count	1-Month Count
2	13	18

[jkotas]

Windows breaking change: https://www.windowscentral.com/microsoft/windows/windows-11-update-killed-localhost-support

[jozkee]

Do you think that could be the same root cause for #120380? It's the exact same test failing:

Process terminated. Assertion failed.
Unexpected error code getting attributes 64 from path \\LOCALHOST\share\path
   at System.Diagnostics.DebugProvider.Fail(String, String) + 0x36
   at System.Diagnostics.Debug.Fail(String, String) + 0x49
   at System.IO.FileSystem.FillAttributeInfo(String, Interop.Kernel32.WIN32_FILE_ATTRIBUTE_DATA&, Boolean) + 0x1d3
   at System.IO.FileSystemInfo.get_ExistsCore() + 0x1e
   at System.IO.FileInfo.get_Exists() + 0xf
   at System.IO.Tests.BaseSymbolicLinks_FileSystem.ResolveLinkTarget_Succeeds(String pathToTarget, Boolean returnFinalTarget) + 0xbd

Other issue console log:

    System.IO.Tests.File_SymbolicLinks.ResolveLinkTarget_Succeeds(pathToTarget: "\\\\LOCALHOST\\share\\path", returnFinalTarget: True) [FAIL]
      System.IO.IOException : The specified network name is no longer available. : 'C:\Windows\Temp\#File_SymbolicLinks_nggppjop.npp\ResolveLinkTarget_Succeeds_163_s2c0jy94.link'.
      Stack Trace:
        /_/src/libraries/System.Private.CoreLib/src/System/IO/FileSystem.Windows.cs(696,0): at System.IO.FileSystem.GetFinalLinkTarget(String linkPath, Boolean isDirectory)
        /_/src/libraries/System.Private.CoreLib/src/System/IO/FileSystem.Windows.cs(528,0): at System.IO.FileSystem.ResolveLinkTarget(String linkPath, Boolean returnFinalTarget, Boolean isDirectory)
        /_/src/libraries/System.Private.CoreLib/src/System/IO/File.cs(1473,0): at System.IO.File.ResolveLinkTarget(String linkPath, Boolean returnFinalTarget)
        /_/src/libraries/System.Runtime/tests/System.IO.FileSystem.Tests/File/SymbolicLinks.cs(31,0): at System.IO.Tests.File_SymbolicLinks.ResolveLinkTarget(String linkPath, Boolean returnFinalTarget)
        /_/src/libraries/System.Runtime/tests/System.IO.FileSystem.Tests/Base/SymbolicLinks/BaseSymbolicLinks.FileSystem.cs(169,0): at System.IO.Tests.BaseSymbolicLinks_FileSystem.ResolveLinkTarget_Succeeds(String pathToTarget, Boolean returnFinalTarget

[jkotas]

Do you think that could be the same root cause for #120380?

Quite likely