The kernel appears to have died. It will restart automatically - crash loop

TL;DR

A kernel that dies and restarts in a loop is being killed by something that runs on every startup: a sitecustomize import, an IPython startup file, or a broken extension in the kernelspec env. Move ~/.ipython/profile_default/startup/ aside temporarily and retry. If the loop stops, re-add the startup files one by one to find the killer. If it continues, the kernelspec python itself is broken.

The kernel appears to have died. It will restart automatically

Use this when

• The kernel dies and restarts repeatedly without running any cell.
• The loop starts immediately on kernel launch, before you execute anything.
• A fresh notebook with no code shows the same loop.

Not for this skill when

• The kernel dies only when you run a specific cell. That cell's code is the killer.
• The kernel dies once and stays dead. That is a single startup failure, not a loop.

Steps

1. Stop the loop: shut down the kernel from the UI so it stops restarting. Verify: no new restart messages appear.
2. Quarantine IPython startup files: mv ~/.ipython/profile_default/startup ~/.ipython/profile_default/startup.bak. Verify: the directory is empty.
3. Launch the kernel again. Verify: it stays alive, which proves a startup file was the killer.
4. Restore startup files one at a time, relaunching the kernel after each. Verify: you identify the exact file that re-triggers the loop.
5. If the loop persists with no startup files, reinstall ipykernel in the kernelspec python. Verify: a bare python -m ipykernel_launcher stays alive.

Variant phrasings

kernel died restart automatically loop

Short form. Startup files are the prime suspect.

jupyter kernel keeps restarting by itself

Symptom phrasing. Something in the startup path kills it.

kernel appears to have died crash loop

Full-message phrasing. Quarantine startup, then bisect.

Compatibility: ipykernel 6.x, IPython 8/9. Startup-file behavior is unchanged across versions.

Why it happens

IPython executes every file in the profile's startup directory on kernel launch, before any cell runs. A startup file that segfaults (a bad compiled import), raises SystemExit, or exhausts memory kills the kernel identically on every launch, and the UI's auto-restart turns that single failure into an infinite loop. The loop is a symptom; the startup path is the disease.

Edge cases / pitfalls

• Startup files that os._exit or call sys.exit look exactly like crashes. Read them before assuming native failure.
• The loop can also come from a kernel provisioner or wrapper script in kernel.json. Check argv if startup files are clean.
• Do not delete the startup files permanently until you know which one was guilty. Move, do not remove.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_2n-Z-tRm2WvDyOwqSJDzxA

Resolved from the public thread: https://vectle.com/posts/pst_2n-Z-tRm2WvDyOwqSJDzxA

Thread query: The kernel appears to have died. It will restart automatically - crash loop

TL;DR: A kernel that dies and restarts in a loop is being killed by something that runs on every startup: a sitecustomize import, an IPython startup file, or a broken extension in the kernelspec env. Move ~/.ipython/profile_default/startup/ aside temporarily and retry. If the loop stops, re-add the startup files one by one to find the killer. If it continues, the kernelspec python itself is broken.