Command Line Option

This article describes built-in commands and its options


Invoke fluentd. Here is supported options:

Usage: fluentd [options]
-s, --setup [DIR=/etc/fluent] install sample configuration file to the directory
-c, --config PATH config file path (default: /etc/fluent/fluent.conf)
--dry-run Check fluentd setup is correct or not
--show-plugin-config=PLUGIN Show PLUGIN configuration and exit(ex: input:dummy)
-p, --plugin DIR add plugin directory
-I PATH add library path
-r NAME load library
-d, --daemon PIDFILE daemonize fluent process
--under-supervisor run fluent worker under supervisor (this option is NOT for users)
--no-supervisor run fluent worker without supervisor
--workers NUM specify the number of workers under supervisor
--user USER change user
--group GROUP change group
-o, --log PATH log file path
--log-rotate-age AGE generations to keep rotated log files
--log-rotate-size BYTES sets the byte size to rotate log files
--log-event-verbose enable log events during process startup/shutdown
-i CONFIG_STRING, inline config which is appended to the config file on-the-fly
--emit-error-log-interval SECONDS
suppress interval seconds of emit error logs
--suppress-repeated-stacktrace [VALUE]
suppress repeated stacktrace
--without-source invoke a fluentd without input plugins
--use-v1-config Use v1 configuration format (default)
--use-v0-config Use v0 configuration format
-v, --verbose increase verbose level (-v: debug, -vv: trace)
-q, --quiet decrease verbose level (-q: warn, -qq: error)
--suppress-config-dump suppress config dumping when fluentd starts
-g, --gemfile GEMFILE Gemfile path
-G, --gem-path GEM_INSTALL_PATH Gemfile install path (default: $(dirname $gemfile)/vendor/bundle)

Important options

-g, --gemfile

Fluentd starts with bundler managed dependent plugins.


Fluentd starts without configuration dump. If you don't want to show configuration in fluentd logs, e.g. don't show private keys, this options is useful.


If set true, suppress stacktrace in fluentd logs. Since v0.12, this option is true by default.


Fluentd starts without input plugins. This option is useful for flushing buffers with no new incoming events.

-i, --inline-config

If you use fluentd on XaaS which doesn't support persistent disks, this option is useful.


If you want to use your supervisor tools, this option avoids double supervisor.

Set via configuration file

Several options could be set via <system> directive configuration file. See configuration file article.


Send event to fluentd's in_forward/in_unix plugin. This is useful for testing.

Usage: fluent-cat [options] <tag>
-p, --port PORT fluent tcp port (default: 24224)
-h, --host HOST fluent host (default:
-u, --unix use unix socket instead of tcp
-s, --socket PATH unix socket path (default: /var/run/fluent/fluent.sock)
-f, --format FORMAT input format (default: json)
--json same as: -f json
--msgpack same as: -f msgpack
--none same as: -f none
--message-key KEY key field for none format (default: message)


Send json message with debug.log tag to local fluentd:

% echo '{"message":"hello"}' | fluent-cat debug.log

Send to other machine:

% echo '{"message":"hello"}' | fluent-cat debug.log --host testserver --port 24225


Generate plugin's configuration document with specified format.

Usage: /Users/cosmo/GitHub/fluentd/vendor/bundle/ruby/2.4.0/bin/fluent-plugin-config-format [options] <type> <name>
Output plugin config definitions
type: input,output,filter,buffer,parser,formatter,storage
name: registered plugin name
--verbose Be verbose
-c, --compact Compact output
-f, --format=FORMAT Specify format. (markdown,txt,json)
-r NAME Load library
-p, --plugin=DIR Add plugin directory


Generate README style document from plugin's config parameters:

fluent-plugin-config-format output null

Generate old style output from plugin's config parameters:

fluent-plugin-config-format -f txt output null


Generate Fluentd plugin project template. It is good for starting to Fluentd plugin development for using new API plugin. In more detail, please refer to the Generating plugin project skeleton section.

Usage: fluent-plugin-generate [options] <type> <name>
Generate a project skeleton for creating a Fluentd plugin
type: input,output,filter,parser,formatter
name: Your plugin name
--[no-]license=NAME Specify license name (default: Apache-2.0)

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.