Merge pull request #3443 from owncloud/backport_3437_2

stable9.1: Document requirement for prefork MPM when using mod_php

admin_manual/installation/source_installation.rst

@@ -281,6 +281,14 @@ Additional Apache Configurations
   CardDAV clients make sure you have configured the correct 
   :ref:`service-discovery-label` URLs.
 
+.. _apache-mpm-label:
+
+Multi-Processing Module (MPM)
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+`Apache prefork`_ has to be used. Don’t use a threaded ``MPM`` like ``event`` or ``worker`` with ``mod_php``,
+because PHP is currently `not thread safe`_.
+
 .. _enabling_ssl_label:
 
 Enabling SSL
@@ -448,3 +456,8 @@ Other Web Servers
 
 `Univention Corporate Server installation 
 <https://github.com/owncloud/documentation/wiki/UCS-Installation>`_
+
+.. Links
+
+.. _Apache prefork: https://httpd.apache.org/docs/2.4/mod/prefork.html
+.. _not thread safe: https://secure.php.net/manual/en/install.unix.apache2.php

admin_manual/installation/system_requirements.rst

@@ -25,7 +25,7 @@ Platform          Options
 ================= =============================================================
 Operating System  Ubuntu 16.04
 Database          MySQL or MariaDB 5.5+
-Web server        Apache 2.4 with mod_php
+Web server        Apache 2.4 with ``prefork`` :ref:`apache-mpm-label` and ``mod_php``
 PHP Runtime       PHP (5.4, 5.5, 5.6, and 7.0)
 ================= =============================================================
 

admin_manual/issues/general_troubleshooting.rst

@@ -142,10 +142,12 @@ Some common problems / error messages found in your logfiles as described above:
   accessing your SQLite database file in your data directory 
   (``data/owncloud.db``). Please check the permissions of this folder/file or 
   if it exists at all. If you're using MySQL please start your database.
-* ``Connection closed / Operation cancelled`` -> This could be caused by wrong 
-  ``KeepAlive`` settings within your Apache config. Make sure that 
-  ``KeepAlive`` is set to ``On`` and  also try to raise the limits of 
-  ``KeepAliveTimeout`` and  ``MaxKeepAliveRequests``.
+* ``Connection closed / Operation cancelled`` or ``expected filesize 4734206 got 458752``
+  -> This could be caused by wrong ``KeepAlive`` settings within your Apache config.
+  Make sure that ``KeepAlive`` is set to ``On`` and  also try to raise the limits of 
+  ``KeepAliveTimeout`` and  ``MaxKeepAliveRequests``. On Apache with ``mod_php`` using
+  a different :ref:`apache-mpm-label` then ``prefork`` could be another reason. Further
+  information is available at the `forums <https://central.owncloud.org/t/expected-filesize-xxx-got-yyy-0/816>`_.
 * ``No basic authentication headers were found`` -> This error is shown in your
   ``data/owncloud.log`` file. Some Apache modules like ``mod_fastcgi``, ``mod_fcgid``
   or ``mod_proxy_fcgi`` are not passing the needed authentication headers to