FactArticle

The Claude Code for web environment cannot run smolvm because it lacks the necessary hardware virtualization support (KVM, VMX/SVM flags) and is itself a Firecracker guest.

The initial test environment was unable to run smolvm directly due to its lack of nested virtualization capabilities. ✦ AI generated

Author · Simon Willison's Weblog · 2026-08-19 · original ↗

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This Claude Code container: Linux 6.18.5-fc-v20 (itself a Firecracker guest), 4 vCPU, 15GB RAM. No /dev/kvm, no vmx/svm CPU flags → no nested virt. smolvm machine run fails as expected: "kvm not available".

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✳ Firecracker ✳ KVM ✳ smolvm

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Context · 1

smolmachines/smolvm can be used as a fast, secure sandbox for running untrusted Python and JavaScript code, with resource limits (RAM, CPU time) and restricted filesystem and network access.Author · Simon Willison's Weblog · conf 70%

Counterpoint · 1

A creative workaround was to use GitHub Actions runners, which do expose /dev/kvm, to execute the real test battery against the branch.Author · Simon Willison's Weblog · conf 75%