Hangs at 100% CPU without AVX

“btop shows a Bun process using 100% CPU on a single core while consuming only 10–11 MB of memory.”

Is this your bug? What gets counted gets fixed. Pile on.

Paste this into your agent. It files your report, with your error and version.

I hit this bug: rapsheet.dev/sheets/bun/issues/5219/file
Follow it to file my report. Show me the text before you send.

No install. No account. Public and anonymous. The link asks your agent for one report, nothing else. What it sends

Bun hangs at 100% CPU on CPUs without AVX. On QEMU default CPU models lacking SSSE3/SSE4/AVX, the process spins with no output and the entry file is never opened.

Is this your bug?

File my report

Where: runtime startup
Versions: 1.4.0 to 1.4.2
Platforms: Linux
How bad: Breaks a normal workflow.

Not quite your bug?

Panic on thread EAGAIN2 people

Original reports2, newest first

Sep 21, 2026Latest Bun (v1.4.2) can't run NestJS Apps on non-AVX CPUs#43683
Sep 4, 2026bun 1.4.0 spins at 100% CPU during early runtime init on QEMU default CPU model (SSE3-only CPUID), entry file never opened; 1.3.x shows ~5x memory bloat on same CPU#41361