try with local rank

src/lerobot/scripts/lerobot_train.py

@@ -14,6 +14,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import logging
+import os
 import time
 from collections.abc import Callable
 from contextlib import nullcontext
@@ -164,8 +165,15 @@ def train(cfg: TrainPipelineConfig, accelerator: Callable | None = None):
     """
     cfg.validate()
 
-    # Check if this is the main process (process_index == 0 or no accelerator)
-    is_main_process = not accelerator or (hasattr(accelerator, 'process_index') and accelerator.process_index == 0) or accelerator.is_main_process
+    # Check if this is the main process
+    # Use LOCAL_RANK environment variable (set by accelerate) for reliable detection
+    local_rank = int(os.environ.get("LOCAL_RANK", -1))
+    if local_rank == -1:
+        # No LOCAL_RANK, check accelerator object or assume main process
+        is_main_process = not accelerator or (hasattr(accelerator, 'is_main_process') and accelerator.is_main_process)
+    else:
+        # LOCAL_RANK is set, main process is rank 0
+        is_main_process = local_rank == 0
 
     if accelerator and not is_main_process:
         # Disable WandB and logging on non-main processes.

src/lerobot/utils/utils.py

@@ -138,8 +138,13 @@ def init_logging(
         logger.removeHandler(handler)
 
     # Check if this is a non-main process in multi-GPU training
-    # Use process_index to be more explicit (main process is index 0)
-    is_non_main_process = accelerator is not None and hasattr(accelerator, 'process_index') and accelerator.process_index != 0
+    # Check environment variables set by accelerate (more reliable than checking accelerator object)
+    local_rank = int(os.environ.get("LOCAL_RANK", -1))
+    is_non_main_process = local_rank > 0
+    
+    # Fallback to accelerator object check if LOCAL_RANK not set
+    if local_rank == -1 and accelerator is not None:
+        is_non_main_process = hasattr(accelerator, 'process_index') and accelerator.process_index != 0
 
     # Write logs to console (only for main process in multi-GPU training)
     if not is_non_main_process: