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.

Example Configuration

out_file is included in Fluentd's core. No additional installation process is required.

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

Please see the Config File article for the basic structure and syntax of the configuration file. For <buffer> section, please check Buffer section cofiguration.

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 configurations 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

The flushed chunk is appended to existence file or not. The default is not appended. By default, out_file flushes each chunk to 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 behaviour, 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.

Here is 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.

utc

Deprecated parameter. Use timekey_use_utc in <buffer> instead.

add_path_suffix

Add path suffix or not. See also path_suffix parameter.

path_suffix

The suffix of output result.

compress

Compresses flushed files using gzip. No compression is performed by default.

recompress

Execute compression again even when buffer chunk is already compressed. Default is false

symlink_path

Create 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.

@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.

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 intermediate buffer file, not 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 also note in 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.

@type dummy tag dummy1

@type dummy tag dummy2

@type file path /tmp/logs/${tag} symlink_path /tmp/logs/current-${tag} @type file

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

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.