There is huge delay starting up logstash 5.0.0-alpha5

Elastic Stack Logstash
1

We're using Elastic Stack 5.0.0-alpha5.
We have very big trouble starting up Logstash.

Logstash won't start up after executing (as a service) over 1+ hours.
Process is alive, but there's no messages or logs even with debug configuration.

Are there anyone know the reasons and workarounds?

Running environment:

Ubuntu 16.04 LTS with java version 1.8.0_101
ElasticStack 5.0.0-alpha5

2

How are you starting it?

3

Starting with "systemctl start logstash.service"

4

So how exactly do you know it takes an hour to start?

5

I'm looking into logstash log file with wrong configuration file.

6

What does that mean?

7

That means I used wrong configuration file intentionally to check start up delay time.
Logstash logs error about wrong configuration file.

Also, I tested with logstash 2.4.0 on the same machine, and it worked fine.
Thanks.