sglang/.claude/skills/clean-startup-log/SKILL.md

name, description, disable-model-invocation

name	description	disable-model-invocation
clean-startup-log	Clean up noisy startup warnings and spurious prints in SGLang server logs. Use when users ask to clean up unwanted warnings, deprecation messages, or third-party noise in the server startup output.	true

Clean Up SGLang Server Startup Logs

Goal: ensure the server startup log is clean and minimal, with no spurious warnings, deprecation messages, or unformatted prints from third-party libraries.

Workflow

1. Launch a server and capture the log

uv run sglang serve --model-path Qwen/Qwen3-8B 2>&1 | tee /tmp/startup_log.txt

Wait until the server prints The server is fired up and ready to roll!, then Ctrl-C.

For TP>1 testing:

uv run sglang serve --model-path Qwen/Qwen3-8B --tp 2 2>&1 | tee /tmp/startup_log.txt

2. Compare against the clean reference log

Read /tmp/startup_log.txt and compare it against the reference log at the bottom of this file. Identify lines that:

• Do NOT have the [timestamp] or [timestamp TPx] logger prefix
• Contain WARNING, deprecated, is deprecated, or similar noise
• Are printed by third-party libraries (transformers, torchao, NCCL, Gloo, tqdm, etc.)
• Are duplicate/redundant with information already logged by SGLang

3. Classify each noisy line

For each noisy line, determine:

Category	Action
SGLang code using wrong API	Fix the SGLang code (e.g., replace deprecated API with new one)
SGLang code logging at wrong level	Change log level (e.g., warning -> debug for non-actionable messages)
Third-party lib prints at import time	Suppress the logger or redirect stdout during that import
C-level print from .so library	Redirect fd 1 during the specific C call, or accept it if too invasive
Real warning the user should see	Keep it

4. Present findings before fixing

List all noisy lines with their source and proposed fix. Ask the user to review before making changes.

5. Apply fixes and verify

After approval, apply fixes one at a time, re-launch the server, and verify each fix works.

Known Noise Sources and Fixes (from past sessions)

1. torchao "Skipping import of cpp extensions due to incompatible torch version"

• Source: torchao/__init__.py — printed via logger.warning() when torch version < 2.11.0
• Trigger: sglang/__init__.py -> _apply_hf_patches() -> _patch_removed_symbols() -> from transformers.models.llama import modeling_llama -> deep import chain -> transformers/quantizers/auto.py -> from .quantizer_torchao import TorchAoHfQuantizer -> imports torchao
• Fix: In hf_transformers_patches.py::_patch_removed_symbols(), temporarily set the torchao logger level to ERROR around the modeling_llama import:

  _torchao_logger = logging.getLogger("torchao")
  _prev_level = _torchao_logger.level
  _torchao_logger.setLevel(logging.ERROR)
  try:
      from transformers.models.llama import modeling_llama
  finally:
      _torchao_logger.setLevel(_prev_level)
  

2. "torch_dtype is deprecated! Use dtype instead!"

• Source: transformers/configuration_utils.py — the torch_dtype property warns via logger.warning_once()
• Trigger: get_hf_text_config() in sglang/srt/utils/hf_transformers/common.py accesses config.torch_dtype
• Fix: Replace all getattr(config, "torch_dtype", ...) with getattr(config, "dtype", ...) and config.torch_dtype = X with config.dtype = X in common.py

3. "BaseImageProcessorFast is deprecated"

• Source: transformers/utils/import_utils.py — the lazy module __getattr__ warns when BaseImageProcessorFast is accessed
• Trigger: base_processor.py and ernie45_vl.py have from transformers import BaseImageProcessorFast at top level. These are imported eagerly via tokenizer_manager.py -> multimodal_processor.py -> base_processor.py, even for non-multimodal models.
• Fix: Replace from transformers import BaseImageProcessorFast with from transformers import BaseImageProcessor and update all isinstance(..., BaseImageProcessorFast) checks to isinstance(..., BaseImageProcessor)

4. "No platform detected. Using base SRTPlatform with defaults."

• Source: sglang/srt/platforms/__init__.py — logger.warning()
• Fix: Change to logger.debug() — this is expected on machines without a platform plugin and not actionable.

5. NCCL version 2.27.7+cuda13.0

• Source: C-level print from libnccl.so during ncclCommInitRank() call
• Status: Accepted as-is. SGLang already logs the version via sglang is using nccl==X.Y.Z. The C-level print cannot be suppressed without redirecting stdout fd, which is too invasive. NCCL_DEBUG=WARN does not suppress it in NCCL 2.27+.

6. [Gloo] Rank X is connected to Y peer ranks

• Source: C++ Gloo library print during process group init
• Status: Accepted as-is. From C++ code inside PyTorch's Gloo backend.

7. torchao SyntaxWarning: invalid escape sequence

• Source: torchao/quantization/quant_api.py — a raw string with unescaped \.
• Status: Upstream torchao bug. Cannot fix from SGLang side.

8. tqdm progress bars (e.g., Multi-thread loading shards, Capturing batches)

• Status: These are expected and useful. They show progress during weight loading and CUDA graph capture. Keep them.

Investigation Techniques

Trace what triggers an import

import sys
_real_import = __builtins__.__import__
def _tracing_import(name, *args, **kwargs):
    if 'TARGET_MODULE' in name:
        import traceback
        print(f'=== Importing {name} ===')
        traceback.print_stack()
    return _real_import(name, *args, **kwargs)
__builtins__.__import__ = _tracing_import

Trace what triggers a logger warning

import logging, traceback
class TraceHandler(logging.Handler):
    def emit(self, record):
        if 'SEARCH_STRING' in record.getMessage():
            traceback.print_stack()
h = TraceHandler()
h.setLevel(logging.WARNING)
logging.getLogger('TARGET_LOGGER_NAME').addHandler(h)

Find C-level prints in .so files

strings /path/to/library.so | grep "SEARCH_STRING"

Reference: Clean Startup Log (TP=1, Qwen3-8B)

[2026-04-27 02:35:53] Attention backend not specified. Use trtllm_mha backend by default.
[2026-04-27 02:35:53] TensorRT-LLM MHA only supports page_size of 16, 32 or 64, changing page_size from None to 64.
[2026-04-27 02:35:54] server_args=ServerArgs(model_path='Qwen/Qwen3-8B', ...)
[2026-04-27 02:35:56] Using default HuggingFace chat template with detected content format: string
[2026-04-27 02:36:03] Init torch distributed begin.
[Gloo] Rank 0 is connected to 0 peer ranks. Expected number of connected peer ranks is : 0
[Gloo] Rank 0 is connected to 0 peer ranks. Expected number of connected peer ranks is : 0
[Gloo] Rank 0 is connected to 0 peer ranks. Expected number of connected peer ranks is : 0
[2026-04-27 02:36:03] Init torch distributed ends. elapsed=0.27 s, mem usage=0.09 GB
[2026-04-27 02:36:04] Load weight begin. avail mem=177.57 GB
[2026-04-27 02:36:04] Found local HF snapshot for Qwen/Qwen3-8B at ...; skipping download.
Multi-thread loading shards: 100% Completed | 5/5 [00:01<00:00,  3.08it/s]
[2026-04-27 02:36:06] Load weight end. elapsed=1.97 s, type=Qwen3ForCausalLM, avail mem=162.30 GB, mem usage=15.28 GB.
[2026-04-27 02:36:06] Using KV cache dtype: torch.bfloat16
[2026-04-27 02:36:06] KV Cache is allocated. #tokens: 992896, K size: 68.18 GB, V size: 68.18 GB
[2026-04-27 02:36:06] Memory pool end. avail mem=25.26 GB
[2026-04-27 02:36:06] Capture cuda graph begin. This can take up to several minutes. avail mem=24.14 GB
[2026-04-27 02:36:06] Capture cuda graph bs [1, 2, 4, ...]
Capturing batches (bs=1 avail_mem=23.54 GB): 100% | 52/52 [00:03<00:00, 16.76it/s]
[2026-04-27 02:36:09] Capture cuda graph end. Time elapsed: 3.74 s. mem usage=0.60 GB. avail mem=23.54 GB.
[2026-04-27 02:36:09] Capture piecewise CUDA graph begin. avail mem=23.54 GB
[2026-04-27 02:36:09] Capture cuda graph num tokens [4, 8, 12, ...]
Compiling num tokens (num_tokens=4): 100% | 74/74 [00:09<00:00, 8.16it/s]
Capturing num tokens (num_tokens=4 avail_mem=21.23 GB): 100% | 74/74 [00:08<00:00, 9.11it/s]
[2026-04-27 02:36:27] Capture piecewise CUDA graph end. Time elapsed: 17.62 s. mem usage=2.32 GB. avail mem=21.22 GB.
[2026-04-27 02:36:28] max_total_num_tokens=992896, chunked_prefill_size=16384, ...
[2026-04-27 02:36:29] INFO:     Started server process [399368]
[2026-04-27 02:36:29] INFO:     Waiting for application startup.
[2026-04-27 02:36:29] Using default chat sampling params from model generation config: ...
[2026-04-27 02:36:29] INFO:     Application startup complete.
[2026-04-27 02:36:29] INFO:     Uvicorn running on http://127.0.0.1:30000 (Press CTRL+C to quit)
[2026-04-27 02:36:30] Prefill batch, #new-seq: 1, #new-token: 64, ...
[2026-04-27 02:36:30] INFO:     127.0.0.1:34916 - "POST /generate HTTP/1.1" 200 OK
[2026-04-27 02:36:30] The server is fired up and ready to roll!

Note: [Gloo] messages and tqdm progress bars are acceptable. The key is no warnings or deprecation messages from transformers, torchao, or other third-party libraries.