[UE 5.8.3][macOS] UBA orphan cleanup shell revokes debugger terminal, causing Python initialization breakpoint

General Issues and Bug Reporting (Unreal Engine)
1

Summary

Launching Unreal Editor under a debugger on this Mac reproducibly stops at FPythonScriptPlugin::InitializePython(). Python reports OSError: [Errno 9] Bad file descriptor / can't initialize sys standard streams.

The editor’s debugger pseudo-terminal starts valid and becomes revoked after its startup UnrealBuildTool SDK helper finishes. Investigation isolates the trigger to UBA’s CreateCallbackLogWriter: its uba-orphankill child creates a new session and executes a shell while retaining the inherited terminal descriptors. The cleanup shell has the debugger pseudo-terminal as its controlling terminal. After its exit, the editor’s shared descriptors become revoked.

What Type of Bug are you experiencing?

Foundation (C++ Tools, Profiling, & Pipeline)

Steps to Reproduce

  1. Create a clean C++ Unreal project using the installed engine. Leave the editor Python plugin enabled.

  2. Build its Development Editor target.

  3. Launch the editor for this project directly under Rider Debug or Xcode’s debugger. A CLI LLDB launch also reproduces:

    xcrun lldb -- '/Users/Shared/Epic Games/UE_5.8/Engine/Binaries/Mac/UnrealEditor.app/Contents/MacOS/UnrealEditor' '/path/to/MyProject/MyProject.uproject' -notraceserver

    Then execute run in LLDB. -notraceserver is an isolation option; it does not prevent the issue.

  4. Observe the Python initialization ensure/breakpoint in PythonScriptPlugin.cpp:1182.

  5. Inspect standard descriptors: fcntl(F_GETFD) succeeds, while fstat fails with EBADF. lsof reports the affected descriptors as (revoked).

Under Rider, stdin was revoked while stdout/stderr remained valid. Under the tested Xcode/CLI LLDB launch, all three descriptors shared one pseudo-terminal and were revoked.

Expected Result

Expected: the startup build helper completes without invalidating editor standard streams; Python initializes and the editor opens.

Observed Result

Actual: Python initialization fails and Unreal stops at an ensure. This also affects a newly created project, without project-specific plugins or a stream-repair workaround.

Affects Versions

5.8

Platform(s)

Mac