g++ "fatal error: Killed signal terminated program cc1plus" in CI

By Kaveh Alemi·Latchkey

When a compile exceeds available memory the kernel OOM killer kills cc1plus, and g++ reports "fatal error: Killed signal terminated program cc1plus". The fix is to reduce peak memory per compile.

What this error means

A heavy translation unit or high parallel job count makes the build die with the Killed cc1plus message, often only on smaller runners.

c++: fatal error: Killed signal terminated program cc1plus
compilation terminated.
make[2]: *** [CMakeFiles/app.dir/big.cpp.o] Error 1

Common causes

How to fix it

Lower the parallel job count

1. Reduce the number of concurrent compiles so total memory fits the runner.
2. Re-run the build and watch peak memory.

# fewer parallel jobs lowers peak memory
cmake --build build --parallel 2

Constrain per-compile memory

For GCC, --param ggc-min-expand and -O1 reduce frontend memory; split very large generated files where possible.

g++ -O1 --param ggc-min-expand=10 -c big.cpp

How to prevent it

• Cap parallel jobs to fit runner memory, split oversized translation units, and reserve LTO for jobs on larger runners so cc1plus is never OOM-killed.

Frequently asked questions

Related guides

References

• CMake documentation
• GitHub Actions documentation