Login via webpage stopped working, being redirected back to login page

Hi everybody,

suddenly my installation behaves like this:

LDAP authentication is being used. When somebody tries to login he is just dropped back to the login screen immediately with no error message.
When you intentionally use a wrong password you are in contrast being told that your credentials are incorrect.

It affects all users, regardless if they have 2 factor auth enabled or not (https://marketplace.owncloud.com/apps/twofactor_totp).

I am not able to login with "admin" (-> "wrong password"). I guess it is not available anymore because of the use of LDAP.

My Android application is still working btw. It is using a generated password specified in the the login area.

My environment:

Those packages are installed on my debian box:

host:/var/www/owncloud# dpkg --list|grep ownc
ii owncloud 9.1.6-1.1 all ownCloud - Server
ii owncloud-deps-php5 9.1.6-1.1 all ownCloud - dependencies for php5
ii owncloud-files 9.1.6-1.1 all ownCloud - Server

Douzens of other applications are using the same 2 Active Directory servers via LDAP with no issues.

No changes to either the AD servers nor the OC installation have been (knowingly) done except for installing updates (no Debian 9 upgrade, yet, only v8 internal).

I couldn't find anything in neither the owncloud.log nor in the apache files access.log and error.log. If I login with correct credentials no entry is logged.

The problem can be reproduced on multiple client-side operating systems and browsers.

Steps taken so far:

  1. At first I thought it might only affect users using 2 factor auth (the assumption proved to be wrong later). But till then I had upgraded the files of the auth plugin in the apps folder. Then OC asked to run occ upgrade from cmdline which I did. However things remained the same.
  2. I decided to uninstall the plugin. Since I could not login via webpage I decided to remove the plugin files and the handful of entries from the apps table. No change.

Does anybody have an idea what I could do?

Best regards,

I was able to solve it myself. Because I had installed cacti on the same host I had set

session.auto_start = 1

in php.ini. However for owncloud it seems it's required to set it to

session.auto_start = 0