The CreateAppHost task failed unexpectedly. MSB4018

user_3113511 0
Viewed 11792

When I try and build my ASP.NET Core project, I continue to get this error message in Visual Studio 2019. When I build it the second time, the error disappears.

Does anyone know what this error means and how to get rid of it?

Thanks!

<CreateAppHost AppHostSourcePath="$(AppHostSourcePath)"
                   AppHostDestinationPath="$(AppHostIntermediatePath)"
                   AppBinaryName="$(AssemblyName)$(TargetExt)"
                   IntermediateAssembly="@(IntermediateAssembly->'%(FullPath)')"
                   WindowsGraphicalUserInterface="$(_UseWindowsGraphicalUserInterface)"
                   Retries="$(CopyRetryCount)"
                   RetryDelayMilliseconds="$(CopyRetryDelayMilliseconds)"
                   />

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visual-studio-2019 asp.net-core visual-studio
9 Answers

Try running visual studio using 'as administrator' option.

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Some of the files which required for complete building may need admin privilege for accessing them. Commonly run Visual Studio has not enough rights to access them

user_62702980

I had a similar problem. The error message for my ASP.NET Core application was

error MSB4018: The "CreateAppHost" task failed unexpectedly.
error MSB4018: System.MissingMethodException: Method not found: 'Void Microsoft.NET.HostModel.AppHost.HostWriter.CreateAppHost(...

I tracked the issue down to the environment variable MSBuildSDKsPath, which pointed to an older SDK version. After unsetting the variable with export MSBuildSDKsPath= the problem was resolved. Alternatively, setting the variable to the most recent SDK also worked: export MSBuildSDKsPath=C:\Program Files\dotnet\sdk\6.0.100-rc.2.21505.57\Sdks (just an example).

I don't remember why I set the variable in the first place, and eliminating it didn't seem to hurt either, I just removed it. It seems that in general, it is just not necessary.

user_42233960

I noticed that my error also noted: System.UnauthorizedAccessException: Access to the path '...\obj\Release\netcoreapp3.1\apphost.exe' is denied.

Deleted the obj folder and rebuild solution resolved the problem for me. Thanks.

user_54260510

If anyone still have this issue, stopping the Virus & threat protection -> Real-time protection, solve the problem.

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EDIT Use dotnet build from console

user_56016570

It was occurred in dotnet build on docker (dotnet-sdk-3.1, dist:CentOS 8.1).

Log:

/usr/lib64/dotnet/sdk/3.1.111/Sdks/Microsoft.NET.Sdk/targets/Microsoft.NET.Sdk.targets(393,5): error MSB4018: The "CreateAppHost" task failed unexpectedly. [<PathToCsproj>.csproj]
 System.IO.IOException: The process cannot access the file '/<PathToCsprojDir>/obj/Debug/netcoreapp3.1/<AssemblyName>' because it is being used by another process. [<PathToCsproj>.csproj]
    at System.IO.FileStream.Init(FileMode mode, FileShare share, String originalPath) in /_/src/System.Private.CoreLib/shared/System/IO/FileStream.Unix.cs:line 86 [<PathToCsproj>.csproj]
    at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, FileOptions options) in /_/src/System.Private.CoreLib/shared/System/IO/FileStream.cs:line 244 [<PathToCsproj>.csproj]
    at System.IO.FileSystem.CopyFile(String sourceFullPath, String destFullPath, Boolean overwrite) in /_/src/System.IO.FileSystem/src/System/IO/FileSystem.Unix.cs:line 25 [<PathToCsproj>.csproj]
    at System.IO.File.Copy(String sourceFileName, String destFileName, Boolean overwrite) in /_/src/System.IO.FileSystem/src/System/IO/File.cs:line 77 [<PathToCsproj>.csproj]
    at Microsoft.NET.HostModel.AppHost.BinaryUtils.CopyFile(String sourcePath, String destinationPath) [<PathToCsproj>.csproj]
    at Microsoft.NET.HostModel.AppHost.HostWriter.CreateAppHost(String appHostSourceFilePath, String appHostDestinationFilePath, String appBinaryFilePath, Boolean windowsGraphicalUserInterface, String assemblyToCopyResorcesFrom) [<PathToCsproj>.csproj]
    at Microsoft.NET.Build.Tasks.CreateAppHost.ExecuteCore() [<PathToCsproj>.csproj]
    at Microsoft.NET.Build.Tasks.TaskBase.Execute() [<PathToCsproj>.csproj]
    at Microsoft.Build.BackEnd.TaskExecutionHost.Microsoft.Build.BackEnd.ITaskExecutionHost.Execute() [<PathToCsproj>.csproj]
    at Microsoft.Build.BackEnd.TaskBuilder.ExecuteInstantiatedTask(ITaskExecutionHost taskExecutionHost, TaskLoggingContext taskLoggingContext, TaskHost taskHost, ItemBucket bucket, TaskExecutionMode howToExecuteTask) [<PathToCsproj>.csproj]

Solution:

Add CopyRetryCount environment variable. After that, it works with warning.

export CopyRetryCount=100
dotnet build --verbosity quiet -c Debug

Acknowledgments:

This answer may be off-topic, but it has similar message. This question has parameter to solve my problem, that was very helpful. Thank you.

user_39272210

this Occasionally happens. Apparently, VS sometimes louse the permission to access some files in the Obj file. There are too possible solution for this:

  1. Close VS and restart as Admin, so that the permissions are granted again

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  1. Close VS > Delete the project Obj folder > Open VS > rebuild project (if VS didn't do it automatically)
user_25612380

What fixed for me was deleting all bin and out folder.

This was caused by using VSCode as admin. Apparently after I build solution with VSCode as admin, some gets messed up resulting with this issue.

user_67751970

For the applications running in dotnet core, fire a command dotnet clean to clean up all your binaries. Then dotnet build and you're good to go!

user_82498390

due to multiple sdk version downloaded in system.

remove that from the c:/

then it remove error

user_6694160
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