splunk.service: Refusing to accept PID outside of service control group about chef-splunk HOT 8 CLOSED

ubuntu@ip-10-0-0-150:~$ systemctl status splunk.service
● splunk.service - Splunk
     Loaded: loaded (/etc/systemd/system/splunk.service; enabled; vendor preset: enabled)
     Active: inactive (dead)
ubuntu@ip-10-0-0-150:~$ sudo systemctl start splunk.service
Job for splunk.service failed because the service did not take the steps required by its unit configuration.
See "systemctl status splunk.service" and "journalctl -xe" for details.
ubuntu@ip-10-0-0-150:~$ systemctl status splunk.service
● splunk.service - Splunk
     Loaded: loaded (/etc/systemd/system/splunk.service; enabled; vendor preset: enabled)
     Active: failed (Result: protocol) since Thu 2020-10-15 13:33:28 UTC; 2s ago
    Process: 3266 ExecStart=/opt/splunkforwarder/bin/splunk start --answer-yes --no-prompt (code=exited, status=0/SUCCESS)

Oct 15 13:33:27 ip-10-0-0-150 systemd[1]: Starting Splunk...
Oct 15 13:33:28 ip-10-0-0-150 splunk[3266]: The splunk daemon (splunkd) is already running.
Oct 15 13:33:28 ip-10-0-0-150 systemd[1]: splunk.service: Refusing to accept PID outside of service control group, acquired through unsafe symlink chain: /opt/splunkforwarder>
Oct 15 13:33:28 ip-10-0-0-150 systemd[1]: splunk.service: Refusing to accept PID outside of service control group, acquired through unsafe symlink chain: /opt/splunkforwarder>
Oct 15 13:33:28 ip-10-0-0-150 systemd[1]: splunk.service: Failed with result 'protocol'.
Oct 15 13:33:28 ip-10-0-0-150 systemd[1]: Failed to start Splunk.

---
driver:
  name: ec2
  region: eu-west-1
  interface: public
  instance_type: t2.medium
  require_chef_omnibus: true
  subnet_filter:
    ...
  security_group_filter:
    ...
  tags:
    ...

transport:
  max_threads: 5
  connection_timeout: 10
  connection_retries: 36
  connection_retry_sleep: 10
  max_wait_until_ready: 1200

provisioner:
  name: chef_zero
  log_level: auto
  product_name: chef
  product_version: 14
  max_retries: 3
  wait_for_retry: 90
  retry_on_exit_code:
    - 35 # chef-client's reboot scheduled exit status
  chef_license: accept
  attributes:
    dev_mode: true
    splunk:
      accept_license: true
      enable_ssl: false
      ssl_options:
        enableSplunkWebSSL: 0
        httpport: 8000
        startwebserver: 1
      web_port: 8000

verifier:
  name: inspec
  sudo: true
  root_path: '/opt/verifier'

platforms:
  - name: ubuntu-2004
    driver:
      image_search:
        owner-id: "099720109477"
        name: ubuntu/images/*/ubuntu-*-20.04*
  - name: ubuntu-1804
    driver:
      image_search:
        owner-id: "099720109477"
        name: ubuntu/images/*/ubuntu-*-18.04*
  - name: ubuntu-1604
    driver:
      image_search:
        owner-id: "099720109477"
        name: ubuntu/images/*/ubuntu-*-16.04*

suites:
  - name: client
    run_list:
      - recipe[chef-splunk::default]
    attributes:
      dev_mode: true
      splunk:
        accept_license: true
    verifier:
      inspec_tests:
        - path: test/integration/default