Hello,
I'm using the syslog output plugin in my Logatsh file conf, but during the execution ( /usr/share/logstash/bin/logstash -f /etc/logstash/conf.d/apache.conf ) of the logstash conf file, it shows multiple errors :
[ERROR] 2019-10-24 11:17:54.088 [Converge PipelineAction::Create] registry - Problems loading a plugin with {:type=>"output", :name=>"syslog", :path=>"logstash/outputs/syslog", :error_message=>"LogStash::Plugins::Registry::UnknownPlugin", :error_class=>LogStash::Plugins::Registry::UnknownPlugin, :error_backtrace=>["/usr/share/logstash/logstash-core/lib/logstash/plugins/registry.rb:256:in namespace_lookup'", "/usr/share/logstash/logstash-core/lib/logstash/plugins/registry.rb:182:inlegacy_lookup'", "/usr/share/logstash/logstash-core/lib/logstash/plugins/registry.rb:156:in block in lookup'", "org/jruby/ext/thread/Mutex.java:165:insynchronize'", "/usr/share/logstash/logstash-core/lib/logstash/plugins/registry.rb:152:in lookup'", "/usr/share/logstash/logstash-core/lib/logstash/plugins/registry.rb:206:inlookup_pipeline_plugin'", "/usr/share/logstash/logstash-core/lib/logstash/plugin.rb:137:in lookup'", "org/logstash/plugins/PluginFactoryExt.java:200:inplugin'", "org/logstash/plugins/PluginFactoryExt.java:184:in plugin'", "/usr/share/logstash/logstash-core/lib/logstash/pipeline.rb:71:inplugin'", "(eval):16:in initialize'", "org/jruby/RubyKernel.java:1061:ineval'", "/usr/share/logstash/logstash-core/lib/logstash/pipeline.rb:49:in initialize'", "/usr/share/logstash/logstash-core/lib/logstash/pipeline.rb:90:ininitialize'", "/usr/share/logstash/logstash-core/lib/logstash/pipeline_action/create.rb:43:in block in execute'", "/usr/share/logstash/logstash-core/lib/logstash/agent.rb:96:inblock in exclusive'", "org/jruby/ext/thread/Mutex.java:165:in synchronize'", "/usr/share/logstash/logstash-core/lib/logstash/agent.rb:96:inexclusive'", "/usr/share/logstash/logstash-core/lib/logstash/pipeline_action/create.rb:39:in execute'", "/usr/share/logstash/logstash-core/lib/logstash/agent.rb:334:inblock in converge_state'"]}
[ERROR] 2019-10-24 11:17:54.100 [Converge PipelineAction::Create] agent - Failed to execute action {:action=>LogStash::PipelineAction::Create/pipeline_id:main, :exception=>"LogStash::PluginLoadingError", :message=>"Couldn't find any output plugin named 'syslog'. Are you sure this is correct? Trying to load the syslog output plugin resulted in this error: Problems loading the requested plugin named syslog of type output. Error: LogStash::Plugins::Registry::UnknownPlugin LogStash::Plugins::Registry::UnknownPlugin", :backtrace=>["/usr/share/logstash/logstash-core/lib/logstash/plugins/registry.rb:211:in lookup_pipeline_plugin'", "/usr/share/logstash/logstash-core/lib/logstash/plugin.rb:137:inlookup'", "org/logstash/plugins/PluginFactoryExt.java:200:in plugin'", "org/logstash/plugins/PluginFactoryExt.java:184:inplugin'", "/usr/share/logstash/logstash-core/lib/logstash/pipeline.rb:71:in plugin'", "(eval):16:ininitialize'", "org/jruby/RubyKernel.java:1061:in eval'", "/usr/share/logstash/logstash-core/lib/logstash/pipeline.rb:49:ininitialize'", "/usr/share/logstash/logstash-core/lib/logstash/pipeline.rb:90:in initialize'", "/usr/share/logstash/logstash-core/lib/logstash/pipeline_action/create.rb:43:inblock in execute'", "/usr/share/logstash/logstash-core/lib/logstash/agent.rb:96:in block in exclusive'", "org/jruby/ext/thread/Mutex.java:165:insynchronize'", "/usr/share/logstash/logstash-core/lib/logstash/agent.rb:96:in exclusive'", "/usr/share/logstash/logstash-core/lib/logstash/pipeline_action/create.rb:39:inexecute'", "/usr/share/logstash/logstash-core/lib/logstash/agent.rb:334:in `block in converge_state'"]}
I've however installed syslog output plugin, following the official documentation (https://www.elastic.co/guide/en/logstash/current/plugins-outputs-syslog.html) and I've checked if it was installed with the "bin/logstash-plugin list --verbose" command
Here is the output :
logstash-codec-cef (5.0.6)
logstash-codec-collectd (3.0.8)
logstash-codec-dots (3.0.6)
logstash-codec-edn (3.0.6)
...
logstash-output-stdout (3.1.4)
logstash-output-syslog (3.0.5)
Here is the conf file :
#input
input {
beats {
port => 5044
}
}
#output
output {
stdout {
codec => rubydebug
}
syslog {
host => "192.168.205.206"
port => 514
protocol => "udp"
}
}
The version of logsatsh running is 6.8.4
Could you please help me ? 
Regards,
Jean-Luc