训练时，报错：data.yaml does not exist

!yolo task=detect mode=train model=yolov8n.pt data=data.yaml

解决办法：

写绝对路径：

!yolo task=detect mode=train model=yolov8n.pt data=/home/{username}/{xxx}/{xxx}/datasets/data.yaml

data.ymal 里path的配置也要是绝对路径：

# path: ../datasets/{your_project}  # dataset root dir
path: /home/{username}/{xxx}/{xxx}/datasets/{your_project}  # dataset root dir

原因

1. cli 传参
   https://github.com/ultralytics/ultralytics/blob/790f9c067c9a3548acf7c6925cea14de9ad77787/ultralytics/yolo/cfg/__init__.py#L183

2. train
   https://github.com/ultralytics/ultralytics/blob/790f9c067c9a3548acf7c6925cea14de9ad77787/ultralytics/yolo/engine/model.py#L294

3. 初始化trainer
   https://github.com/ultralytics/ultralytics/blob/790f9c067c9a3548acf7c6925cea14de9ad77787/ultralytics/yolo/engine/trainer.py#L75

4. 获取参数
   https://github.com/ultralytics/ultralytics/blob/790f9c067c9a3548acf7c6925cea14de9ad77787/ultralytics/yolo/cfg/__init__.py#L87

5. 加载data.ymal
   https://github.com/ultralytics/ultralytics/blob/790f9c067c9a3548acf7c6925cea14de9ad77787/ultralytics/yolo/engine/trainer.py#L122

6. 拼接data.ymal 文件路径
   https://github.com/ultralytics/ultralytics/blob/790f9c067c9a3548acf7c6925cea14de9ad77787/ultralytics/yolo/data/utils.py#L220
   
   这里可以看到，如果不写成绝对路径，则按DATASETS_DIR去拼接，
   过程是：yolo先找到user_config_dir
   /home/{user}/.config，
   第一次运行yolo项目A时，会在下面创建/home/{user}/.config/Ultralytics
   和/home/{user}/.config/Ultralytics/settings.yaml
   setting.ymal 里会有DATASETS_DIR，值就是项目A的datasets路径。

datasets_dir: /home/{user}/{projectA}/datasets