Note: this article was originally written for Chamilo 1.9 but it is also valid for all versions 1.10 and 1.11.
We seldom receive a request from users of Chamilo LMS saying their sessions are cut in the middle of their activity. And sure, it might so happen that you are in the middle of the redaction of a very large answer to an open question, or diserting on how the course is going to help you in the forum. And we get that it's super-frustrating to click "submit" and then get an error page. We do, really.
Now on our side of the fence, we have to cover a series of non-trivial issues...
If you leave a session open for too long, another user might hack your session and get inside the system in your place (unless you use an unflawed SSL certificate to protect your communication).This is generally OK if you are a student, but what if you are an administrator or if you are viewing super-confidential learning content?
Another issue you might have is leaving a public computer without closing your session, and have someone else "follow you" and use your session. This leads to the same problem as above. Finally, not cleaning the sessions from time to time inevitably leads to thousands (or rather hundreds of thousands) of sessions being handled by the server, which inevitably leads to a slow server.
So in the best interest of all, it is important to have a balanced session time. We generally consider that 2 hours is a reasonnable total time. If you've been inactive for two hours, then it's reasonable to get disconnected when you come back. 'cause honestly, you weren't really studying, were you?
But even with that, we still got complaints from the users, so we decided to put it at 100 hours. OK, so that's 4 days and 4 hours. Enough, right? That's the default setting in Chamilo, and you can find it in your main/inc/conf/configuration.php on the line that says:
// Session lifetime
$_configuration['session_lifetime'] = 360000;
That's the value that comes with a default installation of Chamilo 1.9.*.
Now, even if you have that, and depending on your PHP settings for session handling, you might still need to change two settings, but these are out of Chamilo's control, directly into PHP's configuration:
session.gc_maxlifetime = 1440
This is the number of seconds after which the garbage collector (a vacuum cleaner, kind of) of PHP considers that session files, on the server, if left untouched, will be erased, and
session.cookie_lifetime = 0
which defines the time (in seconds) that the cookie will ask to the browser to be stored for. If 0, it means that it will stay there until the browser is closed. If anything more than 0, it will stay there for that number of seconds.
Now... the funny thing here (which makes it even harder to track) is that if you use the default session handler of PHP, called "file", the time used for the garbage collector to erase the sessions files is *not* the last time the session was accessed, but rather the last time the session was *modified*. This means that, if you have some AJAX block refreshing every 30 seconds or so, this will *not* maintain the session active, unless this AJAX refresh actually modifies something to be stored in the session.
So there are many factors to take into account. Our preferred/recommended setup?
$_configuration['session_lifetime'] = 10800; // 3h
Then, in your PHP config:
session.gc_maxlifetime = 10800
session.cookie_lifetime = 0
But now you know how it works, you can tune it as well.
Kudos to Gumbo on Stackoverflow for the missing bits: http://stackoverflow.com/questions/520237/how-do-i-expire-a-php-session-after-30-minutes