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Your LimeSurvey version: 5.3.5
Own server or LimeSurvey hosting: Own
Survey theme/template: Custom
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Since some time now, respondents complain about session timeouts. What is the best way to approach this? How to find out what is happening? Any best practice?

www.limesurvey.org/manual/Troubleshootin...ssion_has_expired.22 (Manual page) did not help me. This mentions "Suhosin" which I have never heard of.

Ask for the exact error message people got.
Try to reproduce the session timeout on your own.
Check PHP setting for session duration and raise the time.
If you raise the timelimit ensure that there is enough storage for sessiondata. Mostly an issue if sessionhandler is filebased, the session directory in php is set to temp and temp is limited in space to prevent bigger files getting placed there. That setup is becoming less common in hosting. You see a dedicated session directory more often in the setups now.

You have to track down PHP error file, and sometime nginx and apache error file.

Whan i don't found : i try SQL session.

Most recent new information: this occurs when people use the "Back" button of the browser and not the "Back" button that is shown on screen lower left corner.

Is this preventable?

You reproduce ?
It must not throw a session time out.

> Is this preventable?

hardly and not really …

This should be preventable, because you can instruct people not to use the back button of the browser, but people are used to using that.
 

PS : the timeout i have sometimes is when i start survey in a tab, when started on another tab.
bugs.limesurvey.org/view.php?id=17778

tammo wrote:

www.limesurvey.org/manual/Troubleshootin...ssion_has_expired.22 (Manual page) did not help me. This mentions "Suhosin" which I have never heard of.
 

If you are the administrator of the webserver running LimeSurvey you will know if you use Suhosin.
Suhosin had it's haydays a few years ago, when this PHP extensions helped getting PHP more secure. The development stalled and a Suhosin NG is trying to become part a everyones PHP setup again. sektioneins.de/en/blog/19-08-05-suhosin-ng.html

If your PHP setup is using Suhosin can be seen via phpinfo. Because Suhosin (the old one) hasn't be tested under PHP 7, you usually don't see Suhosin running under PHP 7 or PHP 8. In a nutshell: PHP 7 and 8 setups don't come with Suhosin preinstalled.

We run on PHP 7 and 8....