exec_filter Output Plugin

The out_exec_filter Buffered Output plugin (1) executes an external program using an event as input and (2) reads a new event from the program output. It passes tab-separated values (TSV) to stdin and reads TSV from stdout by default.

Table of Contents

Example Configuration

out_exec_filter is included in Fluentd’s core. No additional installation process is required.

<match pattern>
  type exec_filter
  command cmd arg arg
  in_keys k1,k2,k3
  out_keys k1,k2,k3,k4
  tag_key k1
  time_key k2
  time_format %Y-%m-%d %H:%M:%S
Please see the Config File article for the basic structure and syntax of the configuration file.


type (required)

The value must be exec_filter.

command (required)

The command (program) to execute. The out_exec_filter plugin passes the incoming event to the program input and receives the filtered event from the program output.


The number of spawned process for command. Default is 1.

If the number is larger than 2, fluentd uses spawned processes by round robin fashion.


Respawn command when command exit. Default is disabled.

If you specify a positive number, try to respawn until specified times. If you specify inf or -1, try to respawn forever.


The format used to map the incoming event to the program input.

The following formats are supported:

  • tsv (default)

When using the tsv format, please also specify the comma-separated in_keys parameter.

in_keys k1,k2,k3
  • json
  • msgpack


The format used to process the program output.

The following formats are supported:

  • tsv (default)

When using the tsv format, please also specify the comma-separated out_keys parameter.

out_keys k1,k2,k3,k4
  • json
  • msgpack
When using the json format, this plugin uses the Yajl library to parse the program output. Yajl buffers data internally so the output isn't always instantaneous.


The name of the key to use as the event tag. This replaces the value in the event record.


The name of the key to use as the event time. This replaces the the value in the event record.


The format for event time used when the time_key parameter is specified. The default is UNIX time (integer).

Buffered Output Parameters

For advanced usage, you can tune Fluentd’s internal buffering mechanism with these parameters.


The buffer type is memory by default (buf_memory). The file (buf_file) buffer type can be chosen as well. If you use file buffer type, buffer_path parameter is required.

buffer_queue_limit, buffer_chunk_limit

The length of the chunk queue and the size of each chunk, respectively. Please see the Buffer Plugin Overview article for the basic buffer structure. The default values are 64 and 8m, respectively. The suffixes “k” (KB), “m” (MB), and “g” (GB) can be used for buffer_chunk_limit.


The interval between data flushes. The default is 60s. The suffixes “s” (seconds), “m” (minutes), and “h” (hours) can be used.


If set to true, Fluentd waits for the buffer to flush at shutdown. By default, it is set to true for Memory Buffer and false for File Buffer.

retry_wait, max_retry_wait

The initial and maximum intervals between write retries. The default values are 1.0 seconds and unset (no limit). The interval doubles (with +/-12.5% randomness) every retry until max_retry_wait is reached. In the default configuration the last retry waits for approximately 131072 sec, roughly 36 hours.

retry_limit, disable_retry_limit

The limit on the number of retries before buffered data is discarded, and an option to disable that limit (if true, the value of retry_limit is ignored and there is no limit). The default values are 17 and false (not disabled). If the limit is reached, buffered data is discarded and the retry interval is reset to its initial value (retry_wait).


The number of threads to flush the buffer. This option can be used to parallelize writes into the output(s) designated by the output plugin. Increasing the number of threads improves the flush throughput to hide write / network latency. The default is 1.

log_level option

The log_level option allows the user to set different levels of logging for each plugin. The supported log levels are: fatal, error, warn, info, debug, and trace.

Please see the logging article for further details.

Last updated: 2016-06-06 04:47:13 UTC

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.