Syslog-ng service will not start using systemctl and SELinux is set to permissive.
原因
One Identity Engineers have found that in version 7.3 of Red Hat (RHEL) that even when SELinux is in Permissive mode, it does not apply to the system label.
解决办法
It is recommended to upgrade to Red Hat (RHEL) version 7.7 or higher as this issue has been known to be resolved in these versions.