Unity "IL2CPP did not run properly" in CI

IL2CPP converts your IL to C++ and compiles it. When it exits non-zero, Unity reports that IL2CPP did not run properly. The underlying error is a missing toolchain, an editor module, or code IL2CPP cannot convert.

What this error means

A player build using the IL2CPP scripting backend fails with "Il2CppCore did not run properly" or "IL2CPP error for ..." and the build does not produce a binary.

unity

Building Library/Bee/artifacts/... failed
Error: Il2CppCore did not run properly!
Exception: C++ code builder is unable to build C++ code.

Common causes

The target build module is not installed

IL2CPP needs the platform module (for example the Linux IL2CPP or Android module). A base editor image without it cannot run the converter.

A C++ toolchain or NDK is missing

IL2CPP compiles generated C++, so a missing compiler (or Android NDK for mobile) breaks the final build step.

How to fix it

Use an image that includes the IL2CPP module

Select a GameCI editor image variant that bundles the IL2CPP/platform module you target.
Confirm the matching toolchain (or NDK) is present for that platform.
Re-run the IL2CPP build.

.github/workflows/ci.yml

- uses: game-ci/unity-builder@v4
  with:
    targetPlatform: StandaloneLinux64
    customImage: unityci/editor:ubuntu-2022.3.21f1-linux-il2cpp-3

Validate against Mono first

Build once with the Mono backend to confirm code correctness, then isolate IL2CPP-specific toolchain or stripping issues.

How to prevent it

Pick an editor image that includes the IL2CPP module for your target.
Provision the Android NDK when building mobile with IL2CPP.
Keep managed stripping levels conservative to avoid conversion failures.