Jupyter Notebook dead Kernel after Anaconda update

Question

I got the following problem. After update Anaconda because I got an error to import skimage.io to a project in Jupyter Notebook an even a greater error appear - Dead Kernel. Right now I could not ever start a project because the Jupyter gives the following error is:

Copy/paste this URL into your browser when you connect for the first time,
to login with a token:
    http://localhost:8888/? 
token=aaf85a5e18489792c87cce65d7a53a0263cd5c08cc7248b 6
[I 00:55:13.451 NotebookApp] Accepting one-time-token-authenticated 
connection from ::1
[I 00:55:31.607 NotebookApp] Kernel started: 608d2190-59e6-4888-b09a- 
e616f67bd5b4
Traceback (most recent call last):
ERROR:tornado.general:Uncaught exception in ZMQStream callback
Traceback (most recent call last):
File "C:\Program Files\Anaconda3\lib\site- 
packages\zmq\eventloop\zmqstream.py", line 432, in _run_callback
callback(*args, **kwargs)
File "C:\Program Files\Anaconda3\lib\site- 
packages\tornado\stack_context.py", line 276, in null_wrapper
return fn(*args, **kwargs)
File "C:\Program Files\Anaconda3\lib\site-packages\ipykernel\kernelbase.py", 
line 283, in dispatcher
return self.dispatch_shell(stream, msg)
File "C:\Program Files\Anaconda3\lib\site-packages\ipykernel\kernelbase.py", 
line 233, in dispatch_shell
self.pre_handler_hook()
File "C:\Program Files\Anaconda3\lib\site-packages\ipykernel\kernelbase.py", 
line 248, in pre_handler_hook
self.saved_sigint_handler = signal(SIGINT, default_int_handler)
File "C:\Program Files\Anaconda3\lib\signal.py", line 47, in signal
handler = _signal.signal(_enum_to_int(signalnum), _enum_to_int(handler))
ValueError: signal only works in main thread  File "C:\Program 
Files\Anaconda3\lib\runpy.py", line 193, in _run_module_as_main
"__main__", mod_spec)

File "C:\Program Files\Anaconda3\lib\runpy.py", line 85, in _run_code
exec(code, run_globals)
File "C:\Program Files\Anaconda3\lib\site-packages\ipykernel_launcher.py", 
line 16, in <module>
app.launch_new_instance()
File "C:\Program Files\Anaconda3\lib\site- 
packages\traitlets\config\application.py", line 658, in launch_instance
app.start()
File "C:\Program Files\Anaconda3\lib\site-packages\ipykernel\kernelapp.py", 
line 477, in start
ioloop.IOLoop.instance().start()
File "C:\Program Files\Anaconda3\lib\site- 
packages\tornado\platform\asyncio.py", line 112, in start
self.asyncio_loop.run_forever()
ERROR:tornado.general:Uncaught exception in zmqstream callback
Traceback (most recent call last):
File "C:\Program Files\Anaconda3\lib\site- 
packages\zmq\eventloop\zmqstream.py", line 450, in _handle_events
self._handle_recv()
File "C:\Program Files\Anaconda3\lib\site- 
packages\zmq\eventloop\zmqstream.py", line 480, in _handle_recv
self._run_callback(callback, msg)
File "C:\Program Files\Anaconda3\lib\site- 
packages\zmq\eventloop\zmqstream.py", line 432, in _run_callback
callback(*args, **kwargs)
File "C:\Program Files\Anaconda3\lib\site- 
packages\tornado\stack_context.py", line 276, in null_wrapper
return fn(*args, **kwargs)
File "C:\Program Files\Anaconda3\lib\site-packages\ipykernel\kernelbase.py", 
line 283, in dispatcher
return self.dispatch_shell(stream, msg)
File "C:\Program Files\Anaconda3\lib\site-packages\ipykernel\kernelbase.py", 
line 233, in dispatch_shell
self.pre_handler_hook()
File "C:\Program Files\Anaconda3\lib\site-packages\ipykernel\kernelbase.py", 
line 248, in pre_handler_hook
self.saved_sigint_handler = signal(SIGINT, default_int_handler)
File "C:\Program Files\Anaconda3\lib\signal.py", line 47, in signal
handler = _signal.signal(_enum_to_int(signalnum), _enum_to_int(handler))
ValueError: signal only works in main thread  File "C:\Program   
Files\Anaconda3\lib\asyncio\base_events.py", line 409, in run_forever

Answer 1

The following packages are required for a brand new installation of jupyter notebook (version 5.6) with conda, so the working version of tornado is 5.1.

ipykernel:          4.8.2-py36_0       conda-forge
ipywidgets:         7.4.0-py_0         conda-forge
jupyter:            1.0.0-py_1         conda-forge
jupyter_client:     5.2.3-py_1         conda-forge
jupyter_console:    5.2.0-py36_0       conda-forge
nbconvert:          5.3.1-py_1         conda-forge
notebook:           5.6.0-py36_0       conda-forge
qtconsole:          4.3.1-py36_0       conda-forge
terminado:          0.8.1-py36_0       conda-forge
tornado:            5.1-py36h470a237_1 conda-forge
widgetsnbextension: 3.4.0-py36_0       conda-forge

To fix this problem, one can manually install the newest version of tornado:

conda install tornado --update

or re-install jupyter notebook from scratch:

conda uninstall jupyter tornado
conda install jupyter

Answer 2

For me, this issue was ipykernel version mis-match. I had installed google-colab which down-graded my ipykernel. After uninstalling google-colab and upgrading ipykernel to latest the problem got solved.

pip uninstall google-colab

pip install --upgrade ipykernel