The legacy sage notebook is deprecated and not available under Python 3.
Please use instead the Jupyter notebook.
Starting the Notebook: Tips and Tricks
This page is intended to complement and extend the docstring for the notebook() function in Sage, which is long and complicated enough as it is!
I think we should have some more extended discussion of the examples from the notebook docstring here, particularly the options for running a public notebook server.
Here's an example of one thing that's probably better here than in the docstring: the timeout parameter is useful if you find that your server is running out of memory, or seriously bogging down with multiple users. Setting a nonzero timeout will kill idle sessions that are needlessly using memory. See this sage-support thread (and particularly kcrisman's comments).
If you are having trouble accessing the notebook server, make sure you specify interface='' when starting the notebook. The tells the notebook server to listen on all network interfaces. Using the incorrect interface line can have strange effects, such as images not showing up in published worksheets!
Example of configuring the Sage notebook using VirtualBox: SageVirtualBox