sgl-project/sglang · error · RuntimeError

Failed to load config from {file_path}: {str(e)}

Error message

Failed to load config from {file_path}: {str(e)}

What it means

The JSON file pointed to by SGLANG_HICACHE_MOONCAKE_CONFIG_PATH could not be opened or parsed (json.load raised). The message includes the path and the underlying exception text (FileNotFoundError, PermissionError, or JSONDecodeError).

Source

Thrown at python/sglang/srt/mem_cache/storage/mooncake_store/mooncake_store.py:121

    standalone_storage: bool
    client_server_address: str
    enable_ssd_offload: bool = False
    ssd_offload_path: Optional[str] = None
    tenant_id: str = DEFAULT_TENANT_ID

    @staticmethod
    def from_file() -> "MooncakeStoreConfig":
        """Load the config from a JSON file."""
        if not envs.SGLANG_HICACHE_MOONCAKE_CONFIG_PATH.is_set():
            raise RuntimeError(
                f"Config file path not set. Please set {envs.SGLANG_HICACHE_MOONCAKE_CONFIG_PATH.name}"
            )
        file_path = envs.SGLANG_HICACHE_MOONCAKE_CONFIG_PATH.get()
        try:
            with open(file_path) as fin:
                config = json.load(fin)
        except Exception as e:
            raise RuntimeError(f"Failed to load config from {file_path}: {str(e)}")

        if (
            "master_server_address" not in config
            and "client_server_address" not in config
        ):
            raise ValueError(
                "Either master_server_address or client_server_address is required in config file"
            )

        return MooncakeStoreConfig(
            local_hostname=config.get(
                "local_hostname", envs.MOONCAKE_LOCAL_HOSTNAME.default
            ),
            metadata_server=config.get(
                "metadata_server", envs.MOONCAKE_TE_META_DATA_SERVER.default
            ),
            global_segment_size=_parse_global_segment_size(
                config.get(

View on GitHub (pinned to 0132848349)

Solutions

1. Validate the path exists and is readable
2. python -m json.tool config.json to find the syntax error
3. Fix the JSON and restart; check mount paths in containers

import json, os
p = os.environ.get('SGLANG_HICACHE_MOONCAKE_CONFIG_PATH')
if p:
    assert os.path.isfile(p) and os.access(p, os.R_OK), f'unreadable: {p}'
    json.load(open(p))  # raises early with precise JSONDecodeError

try:
    cfg = MooncakeStoreConfig.from_file()
except RuntimeError as e:
    if 'Failed to load config from' in str(e):
        show_config_lint_error(e.__cause__)  # actionable JSON error
        raise

When it happens

Trigger: from_file() with a nonexistent/wrong path, unreadable file, malformed JSON (trailing commas, comments), or an empty file.

Common situations: Typo in the env var path; config mounted at a different path in the container; JSON written by hand with comments or single quotes.

Related errors

• Failed to parse JSON content from file {normalized_input}
• Invalid JSON mapping: {normalized_input}
• Invalid format: expected a mapping from GPU id to IB device
• Invalid format: keys must be integers (or string representat
• No valid GPU mappings found in JSON

AI-assisted analysis of sgl-project/sglang@0132848349 (2026-08-28). Data as JSON: /api/errors/cd0f549b578d355b. Report an issue: GitHub.