White screen on LimeSurvey administration panel

Today I tried to update LimeSurvey from 3.5.3 (Mar 16, 2018) to 3.15.9 (January 14, 2019) and got a white screen on the administration panel starting from 3.10.0 (June 11, 2018):

• https://survey.tails.boum.org/index.php/admin/authentication/sa/login

What I did (with a few more trials and errors in between):

• Try to update straight to 3.15.9: white screen!
• Rolled back to 3.5.3: works!
• Bisected until I identified 3.10.0 as the first version with the white screen.
• Rolled back to 3.9.0 and updated the database.
• Updated again to 3.10.0: white screen again!

I also tried to:

• Have a look at the Apache access and error logs: nothing in there.
• Restart Apache: both /bin/systemctl restart apache2.service and systemctl restart apache2.service failed, systemctl status apache2.service was not very informative either.

My questions are:

• How can I further debug this white screen?
• Could I have more such debugging permissions in the future?
• Is there anything to fix so I can restart Apache in the future (though it’s probably not the fix for this time)?

Assigning this ticket to intrigeri as a start as he’s the one who set up LimeSurvey, though this sounds more like a task for the sysadmin on duty.

This is blocking me for the VeraCrypt success metrics (#15977 (closed)) that are not so urgent but the last remaining bit of Sponsor_W.

Related issues

• Blocks #15977 (closed)

Original created by @sajolida on 16549 (Redmine)