What version of Ruby does fluentd support?

Latest fluentd works on Ruby 2.4 or later.

If you want to run fluentd on ruby 2.3 or earlier, use fluentd 1.8 or earlier versions.

When will td-agent be released with Fluentd v1?

Use td-agent 3. It includes v1.

What is the differences between v1 or v0.14?

No differences. v1 is built on top of v0.14. Use v1 for newer installation. We use v1 or v1.x on our document.

Known Issue

Zlib::DataError happens when Output plugin uses gzip compression

This is caused by thread handling mismatch between output thread and gzip library. Output's retry mechanism automatically recovers this error.

Fluentd v1.3 has already fixed this problem.


I have a weird timestamp value, what happened?

The timestamps of Fluentd and its logger libraries depend on your system's clock. It's highly recommended that you set up NTP on your nodes so that your clocks remain synced with the correct clocks.

I installed td-agent and want to add custom plugins. How do I do it?

Use td-agent bundled gem. See this section for more information.

How can I match (send) an event to multiple outputs?

You can use the copy output plugin to send the same event to multiple output destinations.

How can I use environment variables to configure parameters dynamically?

Use "#{ENV['YOUR_ENV_VARIABLE']}". For example,

some_field "#{ENV['FOO_HOME']}"

(Note that it must be double quotes and not single quotes)

Fluentd raises an error for host:port. Why?

There are several reasons:

  • If you get Address already in use error, other process has already

    used host:port. Check port conflict between processes / plugins.

  • If you get Permission denied error, you try to use well-known

    port. Search well-known port for how to use well-known port. Use

    capabilities or something

If you get other errors, google it.

I got "no patterns matched" in the log, why?

This means you emit the event but no <match> directive for emitted event. For example, if you emit the event with foo.bar tag, you need to define <match> for foo.bar tag like <match foo.**>.

See also: Life of a Fluentd event or Config File

File buffer doesn't work properly, why?

file buffer has limitations. Check buf_file article.

I got encoding error inside plugin. How to fix it?

You may hit "\xC3" from ASCII-8BIT to UTF-8 like UndefinedConversionError in the plugin. This error happens when string encoding is set to ASCII-8BIT but actual content is UTF-8. Fluentd and almost plugins treat the logs as a ASCII-8BIT by default but some libraries assume the log encoding is UTF-8. This is why this error happens.

There are several approaches to avoid this problem.

  • Set encoding correctly.

  • Use yajl(Yajl.load/Yajl.dump) instead of json when error happens inside


Fluentd warns "Oj is not installed, and failing back to Yajl for json parser"

If you are using Alpine Linux, you need to install ruby-bigdecimal to use Oj as the JSON parser. Please Execute the following command and see if the warning still shows up.

# apk add --update ruby-bigdecimal

Plugin Development

How do I develop a custom plugin?

Please refer to the Plugin Development Guide.


How can I parse <my complex text log>?

If you are willing to write Regexp, fluentd-ui's in_tail editor or Fluentular is a great tool to verify your Regexps.

If you do NOT want to write any Regexp, look at the Grok parser.

If this article is incorrect or outdated, or omits critical information, please let us know. Fluentd is a open source project under Cloud Native Computing Foundation (CNCF). All components are available under the Apache 2 License.