Upgrade from 5.6.6 to 6.2.4, elastic failed to start

[Ant]

Continuing the discussion from Elasticsearch Service won't start after full cluster upgrade from 5.4 to 6.0:

@warkolm

Please make sure you upgrade the service files when you upgrade Elasticsearch.

You should not be changing these!!!! We may be making changes to them, and any changes you are making are better done in other config files, to stop issues like these happening.

I'm mid upgrade from 5.6.6. to 6.2.4 and haivng an issue getting elastic to start, if I look in /usr/lib/systemd/system/elasticsearch.service I also see the line with -Edefault.path.conf=${CONF_DIR}

I have added path.config and path.log to the elasticsearch.yml file

opened /etc/sysconfig/elasticsearch and added ES_PATH_CONF=/etc/elasticsearch

but when I try to start it I'm getting

● elasticsearch.service - Elasticsearch
   Loaded: loaded (/usr/lib/systemd/system/elasticsearch.service; enabled; vendor preset: disabled)
   Active: failed (Result: exit-code) since Thu 2018-04-19 16:48:16 BST; 5min ago
     Docs: http://www.elastic.co
  Process: 40345 ExecStartPre=/usr/share/elasticsearch/bin/elasticsearch-systemd-pre-exec (code=exited, status=203/EXEC)
 Main PID: 21347 (code=exited, status=143)

Apr 19 16:48:16 opselastic1 systemd[1]: Starting Elasticsearch...
Apr 19 16:48:16 opselastic1 systemd[1]: elasticsearch.service: control process exited, code=exited status=203
Apr 19 16:48:16 opselastic1 systemd[1]: Failed to start Elasticsearch.
Apr 19 16:48:16 opselastic1 systemd[1]: Unit elasticsearch.service entered failed state.
Apr 19 16:48:16 opselastic1 systemd[1]: elasticsearch.service failed.

I'm guessing there is something I've missed but as elastic is putting nothing to the logs I'm not sure what it may be. out of desperation I tried the suggestions to change /usr/lib/systemd/system/elasticsearch.service but it made no difference.

[Ant]

Job for elasticsearch.service failed because the control process exited with error code

Upgrading from 5.6.1 to 6.0.0. I install and when trying to start elasticsearch, it fails. Any ideas why?

following guidance from this post although it's an ubuntu build and I'm running Centos the issues are the same. An engineer here says that /usr/share/elasticsearch/bin/elasticsearch-systemd-pre-exec was removed from 6 so it will never work so I made the changes that there recommended against by the elastict team memeber in the origionally quoated post plus removed that line and my install started. I'm still having issues talking to it but I'm going to create a new thread for that as it's a fresh issue. For those who found this and then find the service starts but they keep getting connection refused, for me there was a elasticsearch.yml.rmpnew which I replaced my config file with, essentially it's just

path.data: /var/lib/elasticsearch
path.logs: /var/log/elasticsearch

which allowed me to interact on localhost, but I don't get responses when I try to add a host ip