systemd plugin for Fluentd
- systemd input plugin to read logs from the systemd journal
- systemd filter plugin for basic manipulation of systemd journal entries
Join the #plugin-systemd channel on the Fluentd Slack
| fluent-plugin-systemd | fluentd | td-agent | ruby |
|---|---|---|---|
| > 0.1.0 | >= 0.14.11, < 2 | 3 | >= 2.1 |
| 0.0.x | ~> 0.12.0 | 2 | >= 1.9 |
| fluent-plugin-systemd | fluentd | fluent-package | ruby |
|---|---|---|---|
| >= 1.1.0 | >= 0.14.11, < 2 | 5 | >= 3.0 |
- The 1.x.x series is developed from this branch (master)
- The 0.0.x series (compatible with fluentd v0.12, and td-agent 2) is maintained on the 0.0.x branch
Simply use RubyGems:
gem install fluent-plugin-systemd -v 1.0.3
or
td-agent-gem install fluent-plugin-systemd -v 1.0.3
If you are upgrading to version 1.0 from a previous version of this plugin take a look at the upgrade documentation. A number of deprecated config options were removed so you might need to update your configuration.
<source>
@type systemd
tag kubelet
path /var/log/journal
matches [{ "_SYSTEMD_UNIT": "kubelet.service" }]
read_from_head true
<storage>
@type local
path /var/log/fluentd-journald-kubelet-cursor.json
</storage>
<entry>
fields_strip_underscores true
fields_lowercase true
</entry>
</source>
<match kubelet>
@type stdout
</match>
<system>
root_dir /var/log/fluentd
</system>
path
Path to the systemd journal, defaults to /var/log/journal
filters
This parameter name is depreciated and should be renamed to matches
matches
Expects an array of hashes defining desired matches to filter the log messages with. When this property is not specified, this plugin will default to reading all logs from the journal.
See matching details for a more exhaustive description of this property and how to use it.
storage
Configuration for a storage plugin used to store the journald cursor.
read_from_head
If true reads all available journal from head, otherwise starts reading from tail, ignored if cursor exists in storage (and is valid). Defaults to false.
entry
Optional configuration for an embedded systemd entry filter. See the Filter Plugin Configuration for config reference.
tag
Required
A tag that will be added to events generated by this input.
<filter kube-proxy>
@type systemd_entry
field_map {"MESSAGE": "log", "_PID": ["process", "pid"], "_CMDLINE": "process", "_COMM": "cmd"}
field_map_strict false
fields_lowercase true
fields_strip_underscores true
</filter>
Note that the following configurations can be embedded in a systemd source block, within an entry block, you only need to use a filter directly for more complicated workflows.
field_map
Object / hash defining a mapping of source fields to destination fields. Destination fields may be existing or new user-defined fields. If multiple source fields are mapped to the same destination field, the contents of the fields will be appended to the destination field in the order defined in the mapping. A field map declaration takes the form of:
{
"<src_field1>": "<dst_field1>",
"<src_field2>": ["<dst_field1>", "<dst_field2>"],
...
}
Defaults to an empty map.
field_map_strict
If true, only destination fields from field_map are included in the result. Defaults to false.
fields_lowercase
If true, lowercase all non-mapped fields. Defaults to false.
fields_strip_underscores
If true, strip leading underscores from all non-mapped fields. Defaults to false.
Given a systemd journal source entry:
{
"_MACHINE_ID": "bb9d0a52a41243829ecd729b40ac0bce"
"_HOSTNAME": "arch"
"MESSAGE": "this is a log message",
"_PID": "123"
"_CMDLINE": "login -- root"
"_COMM": "login"
}
The resulting entry using the above sample configuration:
{
"machine_id": "bb9d0a52a41243829ecd729b40ac0bce"
"hostname": "arch",
"msg": "this is a log message",
"pid": "123"
"cmd": "login"
"process": "123 login -- root"
}
This is commonly caused when the user running fluentd does not have the correct permissions to read the systemd journal.
According to the systemd documentation:
Journal files are, by default, owned and readable by the "systemd-journal" system group but are not writable. Adding a user to this group thus enables her/him to read the journal files.
Ideally you want to ensure that your logs are saved to the systemd journal as a single entry regardless of how many lines they span.
It is possible for applications to naively support this (but only if they have tight integration with systemd it seems) see: systemd/systemd#5188.
Typically you would not be able to this, so another way is to configure your logger to replace newline characters with something else. See this blog post for an example configuring a Java logging library to do this https://fabianlee.org/2018/03/09/java-collapsing-multiline-stack-traces-into-a-single-log-event-using-spring-backed-by-logback-or-log4j2/
Another strategy would be to use a plugin like fluent-plugin-concat to combine multi line logs into a single event, this is more tricky though because you need to be able to identify the first and last lines of a multi line message with a regex.
- Install the systemd dependencies if required
- You can use an offical fluentd docker image as a base, (choose the debian based version, as alpine linux doesn't support systemd).
- Bind mount
/var/log/journalinto your container.
This commonly occurs when a loop is created when fluentd is logging to STDOUT, and the collected logs are then written to the systemd journal. This could happen if you run fluentd as a systemd serivce, or as a docker container with the systemd log driver.
Workarounds include:
- Use another fluentd output
- Don't read every message from the journal, set some
matchesso you only read the messages you are interested in. - Disable the systemd log driver when you launch your fluentd docker container, e.g. by passing
--log-driver json-file
For an example of a full working setup including the plugin, take a look at the fluentd kubernetes daemonset
This plugin depends on libsystemd
On Debian or Ubuntu you might need to install the libsystemd0 package:
apt-get install libsystemd0
On AlmaLinux or RHEL you might need to install the systemd package:
yum install -y systemd
If you want to do this in a AlmaLinux docker image you might first need to remove the fakesystemd package.
yum remove -y fakesystemd
To run the tests with docker on several distros simply run rake
For systems with systemd installed you can run the tests against your installed libsystemd with rake test
Issues and pull requests are very welcome.
If you want to make a contribution but need some help or advice feel free to message me @errm on the Fluentd Slack, or send me an email edward-robinson@cookpad.com
We have adopted the Contributor Covenant and thus expect anyone interacting with contributors, maintainers and users of this project to abide by it.
Many thanks to our fantastic contributors