Error: undefined local variable or method 'log' for module OS

[tmysik]

Just tried to use fluent-plugin-oci-logging plugin (with instance principal) with the latest Fluentd v6. If the plugin is not configured/used, Fluentd works. Whenever one wants to use/configure the plugin, this error occurs:

2025-11-13 13:11:21 +0000 [error]: fluent/log.rb:414:: unexpected error error_class=NameError error="undefined local variable or method 'log' for module OS"
  2025-11-13 13:11:21 +0000 [debug]: command/fluentd.rb:362:: /opt/fluent/lib/ruby/gems/3.4.0/gems/fluent-plugin-oci-logging-1.0.12/lib/fluent/plugin/os.rb:48:in 'OS.os_name_ubuntu?'
  2025-11-13 13:11:21 +0000 [debug]: command/fluentd.rb:362:: /opt/fluent/lib/ruby/gems/3.4.0/gems/fluent-plugin-oci-logging-1.0.12/lib/fluent/plugin/os.rb:27:in 'OS.ubuntu?'
  2025-11-13 13:11:21 +0000 [debug]: command/fluentd.rb:362:: /opt/fluent/lib/ruby/gems/3.4.0/gems/fluent-plugin-oci-logging-1.0.12/lib/fluent/plugin/logging_setup.rb:226:in 'Fluent::Plugin::PublicLoggingSetup#set_default_ca_file'
  2025-11-13 13:11:21 +0000 [debug]: command/fluentd.rb:362:: /opt/fluent/lib/ruby/gems/3.4.0/gems/fluent-plugin-oci-logging-1.0.12/lib/fluent/plugin/logging_setup.rb:172:in 'Fluent::Plugin::PublicLoggingSetup#get_signer'
  2025-11-13 13:11:21 +0000 [debug]: command/fluentd.rb:362:: /opt/fluent/lib/ruby/gems/3.4.0/gems/fluent-plugin-oci-logging-1.0.12/lib/fluent/plugin/out_oci_logging.rb:52:in 'Fluent::Plugin::OCILoggingOutput#configure'
  2025-11-13 13:11:21 +0000 [debug]: command/fluentd.rb:362:: /opt/fluent/lib/ruby/gems/3.4.0/gems/fluentd-1.19.0/lib/fluent/plugin.rb:187:in 'Fluent::Plugin::FeatureAvailabilityChecker#configure'
  2025-11-13 13:11:21 +0000 [debug]: command/fluentd.rb:362:: /opt/fluent/lib/ruby/gems/3.4.0/gems/fluentd-1.19.0/lib/fluent/agent.rb:132:in 'Fluent::Agent#add_match'
  2025-11-13 13:11:21 +0000 [debug]: command/fluentd.rb:362:: /opt/fluent/lib/ruby/gems/3.4.0/gems/fluentd-1.19.0/lib/fluent/agent.rb:74:in 'block in Fluent::Agent#configure'
  2025-11-13 13:11:21 +0000 [debug]: command/fluentd.rb:362:: /opt/fluent/lib/ruby/gems/3.4.0/gems/fluentd-1.19.0/lib/fluent/agent.rb:64:in 'Array#each'
  2025-11-13 13:11:21 +0000 [debug]: command/fluentd.rb:362:: /opt/fluent/lib/ruby/gems/3.4.0/gems/fluentd-1.19.0/lib/fluent/agent.rb:64:in 'Fluent::Agent#configure'
  2025-11-13 13:11:21 +0000 [debug]: command/fluentd.rb:362:: /opt/fluent/lib/ruby/gems/3.4.0/gems/fluentd-1.19.0/lib/fluent/root_agent.rb:184:in 'Fluent::RootAgent#configure'
  2025-11-13 13:11:21 +0000 [debug]: command/fluentd.rb:362:: /opt/fluent/lib/ruby/gems/3.4.0/gems/fluentd-1.19.0/lib/fluent/engine.rb:107:in 'Fluent::EngineClass#configure'
  2025-11-13 13:11:21 +0000 [debug]: command/fluentd.rb:362:: /opt/fluent/lib/ruby/gems/3.4.0/gems/fluentd-1.19.0/lib/fluent/engine.rb:82:in 'Fluent::EngineClass#run_configure'
  2025-11-13 13:11:21 +0000 [debug]: command/fluentd.rb:362:: /opt/fluent/lib/ruby/gems/3.4.0/gems/fluentd-1.19.0/lib/fluent/supervisor.rb:720:in 'Fluent::Supervisor#run_supervisor'
  2025-11-13 13:11:21 +0000 [debug]: command/fluentd.rb:362:: /opt/fluent/lib/ruby/gems/3.4.0/gems/fluentd-1.19.0/lib/fluent/command/fluentd.rb:362:in '<top (required)>'
  2025-11-13 13:11:21 +0000 [debug]: command/fluentd.rb:362:: <internal:/opt/fluent/lib/ruby/3.4.0/rubygems/core_ext/kernel_require.rb>:136:in 'Kernel#require'
  2025-11-13 13:11:21 +0000 [debug]: command/fluentd.rb:362:: <internal:/opt/fluent/lib/ruby/3.4.0/rubygems/core_ext/kernel_require.rb>:136:in 'Kernel#require'
  2025-11-13 13:11:21 +0000 [debug]: command/fluentd.rb:362:: /opt/fluent/lib/ruby/gems/3.4.0/gems/fluentd-1.19.0/bin/fluentd:15:in '<top (required)>'
  2025-11-13 13:11:21 +0000 [debug]: command/fluentd.rb:362:: /opt/fluent/bin/fluentd:25:in 'Kernel#load'
  2025-11-13 13:11:21 +0000 [debug]: command/fluentd.rb:362:: /opt/fluent/bin/fluentd:25:in '<main>'

My environment:

• Oracle Linux 10 (an OCI instance in the Frankfurt region)
• Fluentd: fluent-package 6.0.0 fluentd 1.19.0 (ed15edc4b7c86c1fcea3fbf326b7c42325e6fc71) (installed manually from an RPM package, following the official guide)
• fluent-plugin-oci-logging: 1.0.12

My Fluentd configuration:

<source>
        @type tail
        path ...
        pos_file ...
        tag log
        read_from_head true

        <parse>
                @type none
        </parse>
</source>

<match log>
        @type oci_logging
        log_object_id ocid1.log.oc1.eu-frankfurt-1....
</match>

[tmysik]

I tried to investigate it a bit and the error itself is:

Unable to detect ubuntu platform due to: undefined method 'exists?' for class File

[tmysik]

The Ruby version seems to be 3.4.0 (it comes bundled with the Fluentd package):

[root@instance1 ~]# ll /opt/fluent/lib/ruby/
total 4
drwxr-xr-x. 34 root root 4096 Oct 16 12:46 3.4.0
drwxr-xr-x.  3 root root   19 Oct 16 12:46 gems
drwxr-xr-x.  3 root root   19 Oct 16 12:46 site_ruby
drwxr-xr-x.  3 root root   19 Oct 16 12:46 vendor_ruby