`start_tcp_server': no acceptor (port is in use or requires root privileges)

[satanowski]

No matter which port (>1024) I use this is what I get every time:

#<Thread:0x00007f796e029b78@/usr/local/lib/ruby/gems/2.6.0/gems/fluent-plugin-websocket-0.1.8/lib/fluent/plugin/out_websocket.rb:35 run> terminated with exception (report_on_exception is true):
Traceback (most recent call last):
        6: from /usr/local/lib/ruby/gems/2.6.0/gems/fluent-plugin-websocket-0.1.8/lib/fluent/plugin/out_websocket.rb:38:in `block in configure'
        5: from /usr/local/lib/ruby/gems/2.6.0/gems/eventmachine-1.2.7/lib/eventmachine.rb:195:in `run'
        4: from /usr/local/lib/ruby/gems/2.6.0/gems/eventmachine-1.2.7/lib/eventmachine.rb:195:in `run_machine'
        3: from /usr/local/lib/ruby/gems/2.6.0/gems/fluent-plugin-websocket-0.1.8/lib/fluent/plugin/out_websocket.rb:39:in `block (2 levels)
 in configure'
        2: from /usr/local/lib/ruby/gems/2.6.0/gems/em-websocket-0.5.2/lib/em-websocket/websocket.rb:46:in `run'
        1: from /usr/local/lib/ruby/gems/2.6.0/gems/eventmachine-1.2.7/lib/eventmachine.rb:531:in `start_server'
/usr/local/lib/ruby/gems/2.6.0/gems/eventmachine-1.2.7/lib/eventmachine.rb:531:in `start_tcp_server': no acceptor (port is in use or requires root privileges) (RuntimeError)

Tested on: fluentd:v1.9-debian-1