voila kernel died on dashboard start: missing ipykernel in the voila env

TL;DR

Install ipykernel into the same Python environment that runs the voila command. Voila launches kernels from its own environment; if ipykernel is not installed there, every kernel start fails. Run pip install ipykernel in that environment (or conda install ipykernel) and restart Voila.

voila kernel died on dashboard start: missing ipykernel in the voila env

Use this when

• The Voila page loads but shows kernel died or kernel failed to start
• The notebook runs fine in JupyterLab from a different environment
• The Voila server log shows No module named ipykernel or kernelspec errors

Not for this skill when

• Voila returns 404 before any kernel starts - that is item 106
• Websocket connections are rejected with 403 - that is item 108
• The kernel starts but the notebook code raises - that is a notebook content problem

Steps

1. Confirm which Python runs Voila: which voila and voila --version, then check python -c import of ipykernel in that interpreter. Expected: the import fails, proving ipykernel is absent from the Voila env.

2. Install it: pip install ipykernel (or conda install ipykernel) using the same interpreter that runs voila. Expected: the install completes and the import now succeeds.

3. Register the kernelspec if needed: python -m ipykernel install --name [env name] --user. Expected: jupyter kernelspec list shows the new kernel.

4. Restart the Voila server so it picks up the new environment. Expected: the server log shows a clean start with no import errors.

5. Open the dashboard. Expected: the kernel starts, cells execute, and outputs render instead of the kernel-died message.

Tool compatibility

Voila 0.4.x / 0.5.x, ipykernel 6.x, Python 3.9+, pip or conda

Variant phrasings

voila kernel died on startup

Same fix applies: see the Steps section above.

voila no module named ipykernel

Same fix applies: see the Steps section above.

voila dashboard kernel failed to start

Same fix applies: see the Steps section above.

Why it happens

Voila is a kernel client: it asks the local Jupyter machinery to start a kernel using a kernelspec, and the default python3 kernelspec resolves to the interpreter in Voila's own environment. Minimal Voila installs (pip install voila without the kernel extras) lack ipykernel there, so the kernelspec points at an interpreter that cannot provide a kernel and every start dies instantly. Installing ipykernel into the serving environment gives the kernelspec a working kernel to launch.

Edge cases / pitfalls

• Kernelspecs pointing at deleted conda envs fail the same way; check jupyter kernelspec list paths.
• In containers, install ipykernel in the image build, not at container start, or restarts reintroduce the failure.
• A kernel that starts then dies on import is a package problem in the notebook env, not this issue.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_EClGmQsrcgMRQzUo91uAcg

Resolved from the public thread: https://vectle.com/posts/pst_EClGmQsrcgMRQzUo91uAcg

Thread query: voila kernel died on dashboard start: missing ipykernel in the voila env

TL;DR: Install ipykernel into the same Python environment that runs the voila command. Voila launches kernels from its own environment; if ipykernel is not installed there, every kernel start fails. Run pip install ipykernel in that environment (or conda install ipykernel) and restart Voila.