Troubleshooting

This page regroups information on the most frequent technical issues that can be encountered on noto and provides advice on how to troubleshoot these issues.

In case of persistent issue or issue not documented on this page, do not hesitate to contact us:

Popups with error messages

Popups with error messages usually mean that your personal server is no longer available. This can happen because of a timeout (after around 20 minutes of inactivity) or because you have reached the maximum limit of the available resources (especially RAM – check limits here).

⚠️ Do not simply dismiss the popup and continue working: your session on the hub may still be active so the interface may look like it works but it actually does NOT! You risk loosing your work!

👉 Log out, wait for 1 minute, then log in again.
Two options are available to log out:

Popups with error messages

Spawn failed / Error 503

If you get an Error 503 page or the error message “Spawn failed”, this means that noto has trouble starting your personal server. This can happen either when a large group of people tries to connect simultaneously or if there is an issue with your own personal server (e.g. you tried to install a lib in the main environment and the installation failed or broke your server).

👉 Log out, wait for 1 minute, then log in again.
Two options are available to log out:

If you have reasons to believe that your personal server is broken, contact us: [email protected].

Server not running

Even when your session on the hub remains active, there are cases where your personal server can stop. In this case, the interface displays the message “Your server is not running”. 

👉 Click on the button “Launch Server”.
If this does not work, log out, wait 1 minute, then log in again.

Interface not loading, white page

A white page (interface not loading) usually indicates heavy traffic on noto, and the server needs time to process the requests.
⚠️ Do NOT refresh the page, you might worsen the issue.

👉 Wait for 1 or 2 more minutes, and if the interface still does not load:

Cells not executing

When the code cells in your notebook do not execute anymore, the problem usually comes from the kernel executing the notebook (e.g. infinite loop, too much memory used). 

👉 Restart the kernel executing the notebook and try again (see this page for how to do this).
👉 You can also check how much memory is used by opening a terminal and typing the command noto_mem (see this section for more detail).

Note: in some cases, a cache issue with Firefox has also generated the same type of symptoms (cells not executing and command line not responding). In such cases, logging out, closing the browser and opening it again has solved the issue.

Cells running very slowly

When executing cells becomes very slow, this is generally a symptom that you use too much resources e.g. too many kernels running, too many notebooks opened, noto opened in multiple browser tabs, heavy computing tasks, large datasets opened/loaded etc.

👉 Close notebooks and shut down unused kernels (see this section for more detail).
👉 Restart the kernel executing the notebook (see this page for how to do this).
If these solutions do not work, log out, wait 1 minute, then log in again (logging out will free up all the resources that may still be used in the background).

Do not hesitate to contact us for help!

Architecture of noto

When troubleshooting technical issues, it can really help to have an understanding of the overall architecture of noto so you can better identify the underlying cause of the issues you observe.

Noto is made of three layers:

  1. Your personal server (in red on the diagram below): this is a Jupyter server that runs the notebooks and kernels. It is individual to each user but the resources (RAM, CPU) are shared among all personal servers (which run on a virtual machine).
  2. The hub (in blue): this is a separate component that manages users, authentication, and spawns individual Jupyter server instances for each user.
  3. Your web client (in yellow): it renders the HTML/CSS/JavaScript code on your computer.
Overall architecture of noto

This architecture has a major implication which is that, as a noto user, you have one separate session on each layer: your session on your web client is separate from your session on the hub, which is separate from your session on your personal server.
As a result:

  • Closing your web session (e.g. closing your web browser) does not close your session on noto (hub + personal server continue to run)
  • The hub can work without any session on the personal server (i.e. you have the impression that the interface works but nothing is executing in the background).