This is without any reasonable idea about SOLR configuration. It just happens to work here. It is also specific to my server, you might severly damage yours if you copy & paste this blindly!
All commands to be executed as root.
apt-get remove --purge solr-common
This also removes the index. I want to re-index anyway.
apt-get remove --purge jetty8
rm -rf /var/lib/jetty8
apt-get autoremove
The last line removes also java here. I want this because I also update java.
Add this line to /etc/apt/sources.list if not already present:
deb http://ftp.de.debian.org/debian/ jessie-backports main
apt-get update
apt-get install openjdk-8-jre-headless
apt-get install unzip #This apparently needed for installation
In a temporary directory: (follow instructions on in solr 5.4 docu)
wget http://www.eu.apache.org/dist/lucene/solr/5.3.1/solr-5.3.1.tgz
tar zxvf solr-5.3.1.tgz solr-5.3.1/bin/install_solr_service.sh --strip-components=2
sudo bash ./install_solr_service.sh solr-5.3.1.tgz #using default installation into /opt
service solr status #Should show its up and running
Check also http://<hostname>:8983/solr whether you see the admin-interface.
Edit /var/solr/solr.in.sh
I just add SOLR_JAVA_MEM="-Xms2g -Xmx2g"for a little more RAM.
This was the trickier part because the config file layout is not well documented. Presumably you should figure out what all the files mean and edit them accordingly. The default used here just happens to work here.
mkdir /var/solr/data/ckan1 "ckan1" is an arbitrary name for the (single) solr-"core"
touch /var/solr/data/ckan1/core.properties
cp -a /opt/solr/server/solr/configsets/basic_configs/conf /var/solr/data/ckan1
mv /var/solr/data/ckan1/conf/schema.xml /var/solr/data/ckan1/conf/schema.xml.orig
ln -s /usr/lib/ckan/default/src/ckan/ckan/config/solr/schema.xml /var/solr/data/ckan1/conf/schema.xml
chown -R solr:solr /var/solr
# restart solr
service solr restart
The admin interface http://<hostname>:8983/solr should now indicate that core "ckan1" is available.
In the init-file, set
solr_url = http://127.0.0.1:8983/solr/ckan1
# Become user `ckan` (might be different for you)
su ckan
# activate virtualenv
source /usr/lib/ckan/default/bin/activate
cd /usr/lib/ckan/default/src/ckan/ckan
paster search-index rebuild -c /etc/ckan/default/production.ini #your init-file might be another one.
# As root, restart the httpd
exit
systemctl restart apache2
Cool man, I've been stuck with this problem for 2 days now...
Thanks