Illegal instruction (core dumped)

TL;DR: your CPU is too old for the default polars build. Install polars-lts-cpu, which is compiled for older instruction sets.

The error

Illegal instruction (core dumped)

Fix it

1. Remove the default build:

   pip uninstall -y polars

2. Install the long-term-support CPU build:

   pip install polars-lts-cpu

   Expected: install completes.

3. Verify:

   python -c "import polars; print(polars.__version__)"

   Expected: imports cleanly, no crash.

When this applies

Use this when import polars crashes the interpreter with illegal instruction on old hardware, VMs masking CPU features, or under emulation.

When it does not apply

If the crash happens on a modern CPU, the install is corrupt; reinstall plain polars. If a different library crashes, this fix does not apply.

Compatibility

polars-lts-cpu tracks polars releases with an older-CPU build. The API is identical; only the compiled code differs.

Root cause

Default polars wheels use modern SIMD instructions for speed. CPUs without those features trap the illegal instruction the moment the native module loads, killing the process before any Python error can surface.

Edge cases

Do not install both polars and polars-lts-cpu in one env; they conflict. Cloud VMs sometimes hide CPU flags; if the LTS build still crashes, the vCPU truly lacks the features and the LTS build is the only option.

GitHub issue pola-rs/polars#19936 reports that importing polars dies with Illegal instruction (core dumped) on older CPUs, because the default wheels are compiled for newer instruction sets. The verified fix: use the polars-lts-cpu distribution, which is built for older CPUs, instead of the default polars package. Full thread: https://github.com/pola-rs/polars/issues/19936