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ModelPilot

ComfyUI stuck for hours "installing custom nodes" — the from-source build hang

Also seen as: "ComfyUI stuck installing custom nodes", "llama-cpp-python build hangs", "sam2 install hangs", "pip install never finishes ComfyUI"

Direct answer

How do I fix "a deploy stuck installing custom nodes"?

A ComfyUI startup that hangs at "installing custom nodes" and never reaches model download is usually one custom node triggering a heavy from-source compile. Packages like llama-cpp-python and sam2 build native/CMake code, and with no timeout one doomed compile — or a pip resolver backtrack — blocks the whole install indefinitely.

Key facts

  • iA custom node’s requirements pull a package that compiles from source (llama-cpp-python, sam2, sometimes xformers) with no prebuilt wheel for your environment.
  • ipip’s resolver backtracking through many versions of a hard-to-satisfy dependency.
  • iNo per-step timeout, so a stuck build looks identical to a slow one.

Next step

  1. 1Add --prefer-binary to the pip install so it takes a prebuilt wheel instead of compiling.
  2. 2Wrap each pip call in a timeout (e.g. timeout 600 pip install ...) so a doomed build is killed and the rest proceeds instead of hanging forever.
  3. 3Pin known-source packages to a wheel via a constraints file (e.g. a specific xformers build).
  4. 4On a headless/cloud deploy, prefer an image that bakes the heavy nodes at build time rather than compiling them at boot.

If that didn't fix it

  • If it is genuinely slow rather than stuck, a big native build can legitimately take 10–20 minutes — check whether the process is actually using CPU before you kill it.

Not sure this workflow will run before you rent a GPU?

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Other ComfyUI errors

Fix

GPU Memory Exhausted

Fix

Model Not Found

Fix

Missing Python Package

Fix

Disk Space Exhausted

Fix

Gated Model Access

Fix

missing custom nodes (node type not found)

Frequently Asked Questions

What causes "a deploy stuck installing custom nodes" in ComfyUI?

A custom node’s requirements pull a package that compiles from source (llama-cpp-python, sam2, sometimes xformers) with no prebuilt wheel for your environment.

How do I fix "a deploy stuck installing custom nodes"?

Add --prefer-binary to the pip install so it takes a prebuilt wheel instead of compiling. Wrap each pip call in a timeout (e.g. timeout 600 pip install ...) so a doomed build is killed and the rest proceeds instead of hanging forever.