you have top stop splunk first. If you started it with root permissions, you have to stop it as "root".
Change owner of /opt/splunk directory to you splunkuser (chown -R splunkuser:splunkgroup /opt/splunk)
Please replace my splunkuser example with the username and the group you did choose to run splunk in you environment.
After you did this, you should try to start is as splunkuser. Afterwards you can set the boot-start by doing the command @klischatb named: /opt/splunk/bin/splunk enable boot-start -user splunkunser
Hope this helps. Please let us know.
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