# Security Considerations¶

The Littlest JupyterHub is in beta state & should not be used in security critical situations. We will try to keep things as secure as possible, but sometimes trade security for massive gains in convenience. This page contains information about the security model of The Littlest JupyterHub.

## System user accounts¶

Each JupyterHub user gets their own Unix user account created when they first start their server. This protects users from each other, gives them a home directory at a well known location, and allows sharing based on file system permissions.

1. The unix user account created for a JupyterHub user named <username> is jupyter-<username>. This prefix helps prevent clashes with users that already exist - otherwise a user named root can trivially gain full root access to your server. If the username (including the jupyter- prefix) is longer than 26 characters, it is truncated at 26 characters & a 5 charcter hash is appeneded to it. This keeps usernames under the linux username limit of 32 characters while also reducing chances of collision.

2. A home directory is created for the user under /home/jupyter-<username>.

3. The default permission of the home directory is change with o-rwx (remove non-group members the ability to read, write or list files and folders in the Home directory).

4. No password is set for this unix system user by default. The password used to log in to JupyterHub (if using an authenticator that requires a password) is not related to the unix user’s password in any form.

5. All users created by The Littlest JupyterHub are added to the user group jupyterhub-users.

## sudo access for admins¶

JupyterHub admin users are added to the user group jupyterhub-admins, which is granted complete root access to the whole server with the sudo command on the terminal. No password required.

This is a lot of power, and they can do pretty much anything they want to the server - look at other people’s work, modify it, break the server in cool & funky ways, etc. This also means if an admin’s credentials are compromised (easy to guess password, password re-use, etc) the entire JupyterHub is compromised.

## Off-boarding users securely¶

When you delete users from the JupyterHub admin console, their unix user accounts are not removed. This means they might continue to have access to the server even after you remove them from JupyterHub. Admins should manually remove the user from the server & archive their home directories as needed. For example, the following command deletes the unix user associated with the JupyterHub user yuvipanda.

sudo userdel jupyter-yuvipanda


If the user removed from the server is an admin, extra care must be taken since they could have modified the system earlier to continue giving them access.

## Per-user /tmp¶

/tmp is shared by all users in most computing systems, and this has been a consistent source of security issues. The Littlest JupyterHub gives each user their own ephemeral /tmp using the PrivateTmp feature of systemd.

## HTTPS¶

Any internet-facing JupyterHub should use HTTPS to secure its traffic. For information on how to use HTTPS with your JupyterHub, see Enable HTTPS.