diff --git a/astrai/config/train_config.py b/astrai/config/train_config.py
index 801edd6..0a60de0 100644
--- a/astrai/config/train_config.py
+++ b/astrai/config/train_config.py
@@ -1,4 +1,4 @@
-from dataclasses import dataclass, field
+from dataclasses import dataclass, field, fields
 from typing import Callable, Optional
 
 import torch.nn as nn
@@ -9,17 +9,21 @@ from torch.utils.data import Dataset
 from astrai.config.base import BaseConfig
 
 
+def required(**kw):
+    return {"required": True, **kw}
+
+
 @dataclass
 class TrainConfig(BaseConfig):
     # basic setting
-    model: nn.Module = field(default=None, metadata={"help": "Model for training."})
-    strategy: str = field(default=None, metadata={"help": "Training strategy."})
-    dataset: Dataset = field(default=None, metadata={"help": "Dataset for training."})
+    model: nn.Module = field(default=None, metadata=required(help="Model for training."))
+    strategy: str = field(default=None, metadata=required(help="Training strategy."))
+    dataset: Dataset = field(default=None, metadata=required(help="Dataset for training."))
     optimizer_fn: Callable[[nn.Module], Optimizer] = field(
-        default=None, metadata={"help": "Optimizer factory for training."}
+        default=None, metadata=required(help="Optimizer factory for training.")
     )
     scheduler_fn: Callable[[Optimizer], LRScheduler] = field(
-        default=None, metadata={"help": "Scheduler factory for training."}
+        default=None, metadata=required(help="Scheduler factory for training.")
     )
     n_epoch: int = field(default=1, metadata={"help": "Number of epochs for training."})
     batch_per_device: int = field(
@@ -76,6 +80,10 @@ class TrainConfig(BaseConfig):
     state_dict_fn: Optional[Callable] = field(
         default=None, metadata={"help": "Parallel function for state  dict saving."}
     )
+    start_method: str = field(
+        default="spawn",
+        metadata={"help": "Multiprocessing start method (spawn/fork/forkserver)."},
+    )
 
     # others
     device_type: str = field(
@@ -89,14 +97,8 @@ class TrainConfig(BaseConfig):
         self.validate()
 
     def validate(self):
-        required_fields = [
-            "model",
-            "strategy",
-            "dataset",
-            "optimizer_fn",
-            "scheduler_fn",
-        ]
-
-        for field_name in required_fields:
-            if getattr(self, field_name) is None:
-                raise ValueError(f"{field_name} is required.")
+        for fld in fields(self):
+            if fld.metadata.get("required") and getattr(self, fld.name) is None:
+                raise ValueError(
+                    f"TrainConfig.{fld.name} is required but got None."
+                )
diff --git a/astrai/parallel/setup.py b/astrai/parallel/setup.py
index 3128a67..7fee102 100644
--- a/astrai/parallel/setup.py
+++ b/astrai/parallel/setup.py
@@ -123,6 +123,7 @@ def spawn_parallel_fn(
     master_addr: str = "localhost",
     master_port: str = "29500",
     device_type: str = "cuda",
+    start_method: str = "spawn",
     **kwargs,
 ):
     # clear environment variables
@@ -156,6 +157,11 @@ def spawn_parallel_fn(
         kwargs,
     )
 
-    mp.spawn(
-        wrapper_spawn_func, nprocs=world_size, args=wrapper_spawn_func_args, join=True
+    mp.start_processes(
+        wrapper_spawn_func,
+        args=wrapper_spawn_func_args,
+        nprocs=world_size,
+        start_method=start_method,
+        join=True,
+        daemon=True,
     )
diff --git a/astrai/trainer/trainer.py b/astrai/trainer/trainer.py
index 2eb565f..4264c47 100644
--- a/astrai/trainer/trainer.py
+++ b/astrai/trainer/trainer.py
@@ -52,6 +52,7 @@ class Trainer:
             master_addr=cfg.master_addr,
             master_port=cfg.master_port,
             device_type=cfg.device_type,
+            start_method=cfg.start_method,
             checkpoint=checkpoint,
         )
 
diff --git a/scripts/tools/train.py b/scripts/tools/train.py
index f04ed3b..db74745 100644
--- a/scripts/tools/train.py
+++ b/scripts/tools/train.py
@@ -149,6 +149,13 @@ def parse_args() -> argparse.Namespace:
     parser.add_argument(
         "--device_type", type=str, default="cuda", help="Device type to use."
     )
+    parser.add_argument(
+        "--start_method",
+        type=str,
+        default="spawn",
+        choices=["spawn", "fork", "forkserver"],
+        help="Multiprocessing start method.",
+    )
 
     args = parser.parse_args()
 
@@ -232,6 +239,7 @@ def train(
     stride: int,
     nprocs: int,
     device_type: str,
+    start_method: str,
 ):
     assert train_type in ["seq", "sft", "dpo", "grpo"]
     assert os.path.exists(param_path)
@@ -314,6 +322,7 @@ def train(
         parallel_wrapper=ddp_wrap,
         state_dict_fn=prepare_checkpoint,
         device_type=device_type,
+        start_method=start_method,
         extra_kwargs=strategy_kwargs,
     )