---
title: "Fine-Tune FLUX.1 for Custom Image Generation — Troubleshooting"
canonical: "https://build.nvidia.com/playbooks/flux-finetuning/troubleshooting.md"
---

# Common issues

The **Hardware platform** column shows where an issue is most relevant. "All hardware platforms" applies to every platform listed in this playbook.

| Symptom | Hardware platform | Cause | Fix |
|---------|-------------------|-------|-----|
| Cannot access gated repo for URL | All hardware platforms | Hugging Face model access restricted or token invalid | Regenerate your [Hugging Face token](https://huggingface.co/docs/hub/en/security-tokens); request access to the [gated model](https://huggingface.co/docs/hub/en/models-gated#customize-requested-information) in a browser; export a valid `HF_TOKEN` before `download.sh` |
| "permission denied" when running Docker | All hardware platforms | User not in the `docker` group | Run `sudo usermod -aG docker $USER && newgrp docker` |
| Container fails to start with GPU error | All hardware platforms | NVIDIA Container Toolkit not configured | Configure the NVIDIA Container Toolkit for Docker and confirm `nvidia-smi` works in a GPU container |
| ComfyUI unreachable on port 8188 | All hardware platforms | Container not running or port blocked | Confirm `launch_comfyui.sh` is running; open `http://localhost:8188` or `http://<HARDWARE_IP>:8188` |
| Training OOM / memory pressure during train or generate | All hardware platforms | Other GPU jobs, residual cache, or workload exceeds available memory | Stop other GPU processes; bring down ComfyUI before training; flush buffer cache (see note); reduce resolution or batch-related settings if needed |
| Memory pressure within capacity | DGX Spark | UMA buffer cache not released | See UMA note below |

> [!NOTE]
> **Unified memory (UMA).** On hardware platforms with unified memory, GPU and CPU share memory dynamically. Some applications have not yet been updated for UMA, so you may hit memory issues even within capacity. If that happens, manually flush the buffer cache:
> ```bash
> sudo sh -c 'sync; echo 3 > /proc/sys/vm/drop_caches'
> ```

For latest known issues, see the documentation linked under **Resources** for your hardware platform.