Hi @ all, 
I've updated ES from 5.6.12 to the latest version and can't start the service anymore.
I've done this with the following steps:
wget -qO - https://artifacts.elastic.co/GPG-KEY-elasticsearch | sudo apt-key add -
echo "deb https://artifacts.elastic.co/packages/6.x/apt stable main" | sudo tee -a /etc/apt/sources.list.d/elastic-6.x.list
apt update && apt install elasticsearch
After This I Have to set ES_PATH_CONF=/etc/elasticsearch in /etc/default/elasticsearch then dpkg finished successfully.
Now when I try to start the service with systemctl start elasticsearch I got the following error:
https://pastebin.com/q1Tzu5H6
When I try to start ES manually as elasticsearch user with sudo -i -u elasticsearch /usr/share/elasticsearch/bin/elasticsearch I get the following error:
https://pastebin.com/CawfYLWG
I use ES with Graylog.
Here all Files:
/etc/default/elasticsearch
https://pastebin.com/zZ9tfGX3
/usr/lib/systemd/system/elasticsearch.service
https://pastebin.com/4Qft9d8Y
/etc/elasticsearch/elasticsearch.yml
https://pastebin.com/dhYtWXZJ
Now I'm stuck and need some help 
Greetings
Ronny
Hi,
I think I have solved my initial issue with setting path.data: and path.logs: to /var/lib/elasticsearch. There is the old Elasticsearch 5.6.12 data stored. I've found the path it with echo $ES_HOME.
Now i get another error that i cant solve anymore.
https://pastebin.com/u03aNFUC
There is an error but but i cant find a solution for this.
Caused by: java.security.AccessControlException: access denied ("java.io.FilePermission" "/etc/graylog/server/ssl/cacerts.jks" "read")
But I don't know how to solve it.
I tried the following without success
chmod 777
chown root:root
chown elasticsearch:elasticsearch
Greetings 
For security reasons, Elasticsearch will only read config files from within its config directory. Is /etc/graylog/server/ssl/ a subdirectory of the Elasticsearch config directory?
Hi,
thanks for reply. 
/etc/graylog/server/ssl/ is the graylog ssl directory.
The Elasticsearch config is ES_PATH_CONF=/etc/elasticsearch
Befor I upgraded Elasticsearch from 5.6.12 to 6.6 this config works without any problems.
How could i solve this?
Just a workaround but it help for the moment.
I just removed-Djavax.net.ssl.trustStore=/etc/graylog/server/ssl/cacerts.jks in /etc/defaults/elasticsearch
Now Elsticsearch starts normaly.