Trying to config a new logstash instance to handle syslog input, so prepared input, output and a dummy working filter as a starting template from another running instance, but not sending any data to input yet. Even so logstash is burning CPU in one thread #15 running bootstrap environment, wonder why and how to stop this useless CO2 generation 
$ curl -XGET 'http://localhost:9600/_node/hot_threads?pretty'
{
"host" : "",
"version" : "6.8.3",
"http_address" : "127.0.0.1:9600",
"id" : "a6cc457a-1610-4e8d-9309-77ce10c865ab",
"name" : "",
"hot_threads" : {
"time" : "2019-09-11T22:59:14+02:00",
"busiest_threads" : 10,
"threads" : [ {
"name" : "Ruby-0-Thread-1",
"thread_id" : 15,
"percent_of_cpu_time" : 96.31,
"state" : "runnable",
"path" : "/usr/share/logstash/lib/bootstrap/environment.rb:6",
"traces" : [ "java.lang.System.identityHashCode(Native Method)", "java.util.IdentityHashMap.hash(Unknown Source)", "java.util.IdentityHashMap.containsKey(Unknown Source)" ]
}, {
"name" : "LogStash::Runner",
"thread_id" : 1,
"percent_of_cpu_time" : 1.2,
"state" : "timed_waiting",
"traces" : [ "java.lang.Object.wait(Native Method)", "java.lang.Thread.join(Unknown Source)", "org.jruby.internal.runtime.NativeThread.join(NativeThread.java:75)" ]
}, {
"name" : "[main]>worker7",
"thread_id" : 36,
"percent_of_cpu_time" : 0.25,
"state" : "timed_waiting",
"traces" : [ "sun.misc.Unsafe.park(Native Method)", "java.util.concurrent.locks.LockSupport.parkNanos(Unknown Source)", "java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(Unknown Source)" ]
}, {
...
Nothing shows in the log than the normal start up:
[2019-09-11T22:39:38,662][INFO ][logstash.pipeline ] Pipeline started successfully {:pipeline_id=>"main", :thread=>"#<Thread:0x239ba8cc sleep>"}
[2019-09-11T22:39:38,709][INFO ][logstash.agent ] Pipelines running {:count=>1, :running_pipelines=>[:main], :non_running_pipelines=>}
[2019-09-11T22:39:39,119][INFO ][logstash.agent ] Successfully started Logstash API endpoint {:port=>9600}