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User sessions

The lino.modlib.users plugin also provides functionality for monitoring user sessions.

See who is working on my site

A site manager can select Site ‣ User sessions to open the Sessions table, which shows who is currently working on this site.

This feature is popular on production sites with relatively few users (less than 100), It requires the database back-end for managing sessions, which is the default behaviour for a Lino site (Lino server administrators usually don’t need to care about How to use sessions).

Limit the number of simultaneous user sessions

A hosting provider can base the pricing of their hosting service on a sessions limit, i.e. a maximum number of allowed user sessions.

The server administrator can configure this value by setting the active_sessions_limit setting of the lino.modlib.users plugin.

An end user might potentially get a message “There are more than X active user sessions. Please try again later” when trying to to log in on a site with a sessions limit.

Dangling user sessions

User sessions can remain in the database even when the user doesn’t actually need them any more. We call them dangling sessions.

Dangling sessions can cause “false alerts” on a site with a sessions limit, i.e. Lino would say “There are more than X active user sessions. Please try again later” although “in reality” these users aren’t actively working on the site.

Don’t mix up dangling sessions with expired sessions. Sessions have a given time to live, and they expire after that time. Expired sessions are never shown in the Sessions table and aren’t taken into account for the sessions limit. Besides using up database space they don’t disturb. Django has an admin command to clean up these periodically (Clearing the session store). The server administrator can configure how long Lino should remember user sessions with the SESSION_COOKIE_AGE setting. The default value for this setting is two weeks.

Dangling sessions can come because user sessions are deleted only when the user logs out explicitly. When a user just closes their browser on one device and logs in from another device, they get a second session, and their first session will remain in the database. Don’t expect Lino to remove this session automatically because after all the user might open their first browser again after some time and expect Lino to remember them.

Other possible reasons for dangling sessions are browsers having the option “Delete cookies and site data when browser is closed”, or private browser sessions. We have seen situations where a same user had more than 1000 dangling sessions.

To help with detecting dangling sessions, Lino adds the Last activity column in the Sessions table. When you see a session with last activity 4 days ago, you may probably assume that it is a dangling session.

There are several ways to handle false sessions limit alerts:

• Reduce the value of SESSION_COOKIE_AGE, e.g. two days instead of two weeks.

• Set SESSION_EXPIRE_AT_BROWSER_CLOSE to True so that sessions expire when the browser closes.

• Instruct users to explicitly log out when they don’t use Lino.

• Increase the sessions limit.

• Have the site manager check Site ‣ Active sessions and manually kill some dangling sessions.

Interactively testing session behaviour

As a developer you can use the lino_book.projects.cosi1 project to interactively explore how Lino behaves regarding sessions. The settings/__init__.py contains some comments. The project also contains a script show_sessions.py to be run using the pm run admin command:

$ pm run show_sessions.py

Concepts

The following concepts have been covered by this documentation page.

sessions limit

The maximum number of simultaneous user sessions that are allowed on a Lino site.

dangling session

A user session that is not yet expired, but isn’t being used actively.

user session

A database entry that is automatically created when a given site user logs in from a given device or browser.