Fluentd

file

The out_file Output plugin writes events to files. By default, it creates files on a daily basis (around 00:10). This means that when you first import records using the plugin, no file is created immediately.

The file will be created when the timekey condition has been met. To change the output frequency, please modify the timekey value.

It is included in Fluentd's core.

Example Configuration

<match pattern>
  @type file
  path /var/log/fluent/myapp
  compress gzip
  <buffer>
    timekey 1d
    timekey_use_utc true
    timekey_wait 10m
  </buffer>
</match>

With this configuration, files named /var/log/fluent/myapp.{%Y%m%d}.log.gz will be generated at one-day intervals.

Please see the Configuration File article for the basic structure and syntax of the configuration file.

For <buffer>, refer to <buffer> Section.

Plugin Helpers

• formatter
• inject
• compat_parameters

Parameters

Common Parameters

@type (required)

The value must be file.

path

The path of the file. The actual path is path + time + ".log" by default. The path parameter supports placeholders, so you can embed time, tag and record fields in the path.

Here is an example:

path /path/to/${tag}/${key1}/file.%Y%m%d
<buffer tag,time,key1>
  # buffer parameters
</buffer>

See <buffer> Section for more detail.

The path parameter is used as <buffer>'s path in this plugin.

Initially, you may see a file which looks like /path/to/file.%Y%m%d/buffer.b5692238db04045286097f56f361028db.log. This is an intermediate buffer file (b5692238db04045286097f56f361028db identifies the buffer). Once the content of the buffer has been completely flushed, you will see the output file without the trailing identifier.

append

Determines whether the flushed chunk is appended to an existing file or not. The default is not appended. By default, out_file flushes each chunk to a different path.

# append false
file.20140608.log_0
file.20140608.log_1
file.20140609.log_0
file.20140609.log_1

This makes parallel file processing easy. But if you want to disable this behavior, you can disable it by setting append true.

# append true
file.20140608.log
file.20140609.log

<format> Directive

The format of the file content. The default @type is out_file.

JSON example:

<format>
  @type json
</format>

See formatter article for more detail.

format

Deprecated parameter. Use <format> instead.

<inject> Section

Add event time and event tag to record.

See Inject Section Configurations for more details.

<buffer> Section

See Buffer Section Configurations for more details.

@type

Overwrites the default value in this plugin.

chunk_keys

Overwrites the default value in this plugin.

timekey

Overwrites the default value in this plugin.

utc

Deprecated parameter. Use timekey_use_utc in <buffer> instead.

add_path_suffix

Add path suffix or not. See also the path_suffix parameter.

path_suffix

The suffix for output result.

compress

Compresses flushed files.

No compression is performed by default.

Supported values:

• text
• gz
• gzip
• zstd (since v1.19.0)

recompress

Performs compression again even if the buffer chunk is already compressed.

Default: false

symlink_path

Creates symlink to temporary buffered file when buffer_type is file. No symlink is created by default. This is useful for tailing file content to check logs.

This is disabled on Windows.

symlink_path_use_relative

Specify whether it creates symlink using relative path in symlink_path. The absolute path is used by default. This parameter is introduced since v1.19.0.

@log_level

The @log_level option allows the user to set different levels of logging for each plugin.

Supported log levels: fatal, error, warn, info, debug, trace

Please see the logging article for further details.

Common Output / Buffer parameters

For common output / buffer parameters, please check the following articles:

• Output Plugin Overview
• Buffer Section Configuration

FAQ

I can see files but placeholders are not replaced, why?

You see an intermediate buffer file, not the output result. The placeholders are replaced during flush buffers.

For example, if you have this setting:

path /path/to/file.${tag}.%Y%m%d

You see following buffer files first:

/path/to/file.${tag}.%Y%m%d/buffer.b5692238db04045286097f56f361028db.log
/path/to/file.${tag}.%Y%m%d/buffer.b5692238db04045286097f56f361028db.log.meta

After flushed, you see actual output result:

/path/to/file.test.20180405.log_0 # tag is 'test'

See the path parameter.

Can I use a placeholder in symlink_path?

Since Fluentd v1.4.0, you can use the placeholder syntax in symlink_path parameter.

For example, suppose you have the following configuration:

<source>
  @type dummy
  tag dummy1
</source>

<source>
  @type dummy
  tag dummy2
</source>

<match dummy*>
  @type file
  path /tmp/logs/${tag}
  symlink_path /tmp/logs/current-${tag}
  <buffer tag,time>
    @type file
  </buffer>
</match>

This produces the following directory layout:

$ tree /tmp/logs/
/tmp/logs/
├── ${tag}
│   ├── buffer.b57fb1dd96306dd0b308e094f7ec2228f.log
│   ├── buffer.b57fb1dd96306dd0b308e094f7ec2228f.log.meta
│   ├── buffer.b57fb1dd96339a870530991d4871cfe11.log
│   └── buffer.b57fb1dd96339a870530991d4871cfe11.log.meta
├── current-dummy1 -> /tmp/logs/${tag}/buffer.b57fb1dd96339a870530991d4871cfe11.log
└── current-dummy2 -> /tmp/logs/${tag}/buffer.b57fb1dd96306dd0b308e094f7ec2228f.log