[bug] Jupyter Notebook Kernel Error

 Traceback (most recent call last):
      File "E:\Anaconda3\envs\fastai\lib\site-packages\tornado\web.py", line 1512, in _execute
        result = yield result
      File "E:\Anaconda3\envs\fastai\lib\site-packages\tornado\gen.py", line 1055, in run
        value = future.result()
      File "E:\Anaconda3\envs\fastai\lib\site-packages\tornado\concurrent.py", line 238, in result
        raise_exc_info(self._exc_info)
      File "", line 4, in raise_exc_info
      File "E:\Anaconda3\envs\fastai\lib\site-packages\tornado\gen.py", line 1063, in run
        yielded = self.gen.throw(*exc_info)
      File "E:\Anaconda3\envs\fastai\lib\site-packages\notebook\services\sessions\handlers.py", line 73, in post
        type=mtype))
      File "E:\Anaconda3\envs\fastai\lib\site-packages\tornado\gen.py", line 1055, in run
        value = future.result()
      File "E:\Anaconda3\envs\fastai\lib\site-packages\tornado\concurrent.py", line 238, in result
        raise_exc_info(self._exc_info)
      File "", line 4, in raise_exc_info
      File "E:\Anaconda3\envs\fastai\lib\site-packages\tornado\gen.py", line 1063, in run
        yielded = self.gen.throw(*exc_info)
      File "E:\Anaconda3\envs\fastai\lib\site-packages\notebook\services\sessions\sessionmanager.py", line 79, in create_session
        kernel_id = yield self.start_kernel_for_session(session_id, path, name, type, kernel_name)
      File "E:\Anaconda3\envs\fastai\lib\site-packages\tornado\gen.py", line 1055, in run
        value = future.result()
      File "E:\Anaconda3\envs\fastai\lib\site-packages\tornado\concurrent.py", line 238, in result
        raise_exc_info(self._exc_info)
      File "", line 4, in raise_exc_info
      File "E:\Anaconda3\envs\fastai\lib\site-packages\tornado\gen.py", line 1063, in run
        yielded = self.gen.throw(*exc_info)
      File "E:\Anaconda3\envs\fastai\lib\site-packages\notebook\services\sessions\sessionmanager.py", line 92, in start_kernel_for_session
        self.kernel_manager.start_kernel(path=kernel_path, kernel_name=kernel_name)
      File "E:\Anaconda3\envs\fastai\lib\site-packages\tornado\gen.py", line 1055, in run
        value = future.result()
      File "E:\Anaconda3\envs\fastai\lib\site-packages\tornado\concurrent.py", line 238, in result
        raise_exc_info(self._exc_info)
      File "", line 4, in raise_exc_info
      File "E:\Anaconda3\envs\fastai\lib\site-packages\tornado\gen.py", line 307, in wrapper
        yielded = next(result)
      File "E:\Anaconda3\envs\fastai\lib\site-packages\notebook\services\kernels\kernelmanager.py", line 160, in start_kernel
        super(MappingKernelManager, self).start_kernel(**kwargs)
      File "E:\Anaconda3\envs\fastai\lib\site-packages\jupyter_client\multikernelmanager.py", line 110, in start_kernel
        km.start_kernel(**kwargs)
      File "E:\Anaconda3\envs\fastai\lib\site-packages\jupyter_client\manager.py", line 259, in start_kernel
        **kw)
      File "E:\Anaconda3\envs\fastai\lib\site-packages\jupyter_client\manager.py", line 204, in _launch_kernel
        return launch_kernel(kernel_cmd, **kw)
      File "E:\Anaconda3\envs\fastai\lib\site-packages\jupyter_client\launcher.py", line 128, in launch_kernel
        proc = Popen(cmd, **kwargs)
      File "E:\Anaconda3\envs\fastai\lib\subprocess.py", line 709, in __init__
        restore_signals, start_new_session)
      File "E:\Anaconda3\envs\fastai\lib\subprocess.py", line 997, in _execute_child
        startupinfo)
    FileNotFoundError: [WinError 2] 系统找不到指定的文件。

起源是安装fastai库时运行conda env update莫名创建了新的环境。
根据解答:

python -m ipykernel install --user

but later on i find this does not work when you have multiple environments. Only one environment will have the full executaion of ipython, others still break.

This blog and this doc truly solve the problem.