From https://www.elastic.co/products/logstash :

Logstash is an open source, server-side data processing pipeline that ingests data from a multitude of sources simultaneously, transforms it, and then sends it to your favorite “stash”.


Here are a few of the settings which you may need to tune in /etc/logstash/logstash.yml.


The maximum number of events an individual worker thread will collect from inputs before attempting to execute its filters and outputs. Larger batch sizes are generally more efficient, but come at the cost of increased memory overhead.


The number of workers that will, in parallel, execute the filter and output stages of the pipeline. If you find that events are backing up, or that the CPU is not saturated, consider increasing this number to better utilize machine processing power.

For more information, please see https://www.elastic.co/guide/en/logstash/current/logstash-settings-file.html.

Logstash Heap

By default, if total available memory is 8GB or greater, the Logstash heap size in /etc/logstash/jvm.options is configured (during setup) to equal 25% of available memory, but no greater than 4GB.

See https://www.elastic.co/guide/en/elasticsearch/guide/current/heap-sizing.html#compressed_oops for more details.

You may need to adjust the value depending on your system’s performance (running sudo so-logstash-restart after).

Adding New Logs or Modifying Existing Parsing


If you are parsing local log files, you may need to add these files to the Syslog-NG configuration in /etc/syslog-ng/syslog-ng.conf and restart the service.


Configuration files for custom parsing can be placed in /etc/logstash/custom/. These will automatically get copied over to the appropriate /etc/logstash/conf.d* directory during the starting of Logstash.


If you are using a distributed or heavy distributed deployment type, it is best practice to put your custom configuration files in the /etc/logstash/custom directory on the Master node. The custom configuration files will then be replicated every 15 minutes or immediately if you use Salt to force the replication to take place.

After adding your custom configuration file(s), restart Logstash and check the log(s) for errors:

sudo so-logstash-restart && sudo tail -f /var/log/logstash/logstash.log


Please note that if you delete or rename config files in /etc/logstash/custom/ then you’ll need to also delete the old files in the appopriate /etc/logstash/conf.d* directories. Otherwise the old config files will remain in /etc/logstash/conf.d* and still be parsed for the actual Logstash configuration.

Mapping Templates

Logstash loads default mapping templates for Elasticsearch to use from /etc/logstash.

The three templates currently being used include:

logstash-template.json - applies to logstash-* indices

logstash-ossec-template.json - applies to logstash-ossec-* indices

beats-template.json - applies to logstash-beats-* indices

Currently, new fields that do not match the template are stored in Elasticsearch, however, they are not indexed, unless provided in a mapping template.

If sending in custom logs to Security Onion that may not match existing fields for existing indices, it is recommended to create a dedicated index for the log source, as well as define a mapping template and output file for the custom log source.

To make sure Logstash can read the custom template:

  1. Place the template in /etc/logstash/custom.
  2. Make sure the template is added to LOGSTASH_OPTIONS in /etc/nsm/securityonion.conf: LOGSTASH_OPTIONS="--volume /etc/logstash/testme-template.json:/testme-template.json:ro"
  3. Make sure the custom template is referenced in the appropriate output file (place the output file in /etc/logstash/custom, then modify it.).
  4. Restart Logstash.

You can check to see if templates are loaded by typing something like the following at a command prompt:

sudo so-elasticsearch-template-list

You can also test the template before restarting Logstash, by using the following command:

sudo so-elasticsearch-template-add

If mappings defined in the template are different than in existing indices, you will receive mapping conflicts in Kibana.

To avoid this, either remove the existing indices, wiping all data, or re-index.


Log file settings can be adjusted in /etc/logstash/log4j2.properties. Currently, logs are set to rollover daily, and configured to be deleted after 7 days.


You can specify your own custom options to be appended to the Logstash startup command, by editing LOGSTASH_OPTIONS in /etc/nsm/securityonion.conf.



From: https://www.elastic.co/guide/en/logstash/current/persistent-queues.html

By default, Logstash uses in-memory bounded queues between pipeline stages (inputs → pipeline workers) to buffer events. The size of these in-memory queues is fixed and not configurable.


From: https://www.elastic.co/guide/en/logstash/current/persistent-queues.html

In order to protect against data loss during abnormal termination, Logstash has a persistent queue feature which will store the message queue on disk. Persistent queues provide durability of data within Logstash.

If you experience adverse effects using the default memory-backed queue, you can configure a disk-based persistent queue by un-commenting the following lines in /etc/logstash/logstash.yaml and modifying the values as appropriate:

#queue.type: persisted
#queue.max_bytes: 1gb

Then restart Logstash:

sudo so-logstash-restart

Queue Max Bytes

The total capacity of the queue in number of bytes. Make sure the capacity of your disk drive is greater than the value >you specify here. If both queue.max_events and queue.max_bytes are specified, Logstash uses whichever criteria is reached >first.

Dead Letter Queue

If you want to check for dropped events, you can enable the dead letter queue. This will write all records that are not able to make it into Elasticsearch into a sequentially-numbered file (for each start/restart of Logstash).

This can be achieved by adding the following to /etc/logstash/logstash.yml:

dead_letter_queue.enable: true

and restarting Logstash:

sudo so-logstash-restart

The dead letter queue files are located in /nsm/logstash/dead_letter_queue/main/.


When using storage nodes, Logstash on the master server outputs to Redis (on the master server). Redis queues events from the Logstash output (on the master) and the Logstash input on the storage node(s) pull(s) from Redis. If you notice new events aren’t making it into Kibana, you may want to first check Logstash on the master, then the redis queue.

Data Fields

Logstash process Zeek logs, syslog, IDS alerts, etc., formatting said data into many different data fields, as described in the Data Fields section.


The Logstash log is located at /var/log/logstash/logstash.log.



[INFO ][logstash.outputs.elasticsearch] retrying failed action with response code: 403 ({"type"=>"cluster_block_exception", "reason"=>"blocked by: [FORBIDDEN/12/index read-only / allow delete (api)];"})

This error is usually caused by the cluster.routing.allocation.disk.watermark (low,high) being exceeded.

You may want to check /var/log/elasticsearch/<hostname>.log to see specifically which indices have been marked as read-only.

Additionally, you can run the following command to allow writing to the affected indices:

curl -XPUT -H 'Content-Type: application/json' localhost:9200/<your_index>/_settings -d'{ "index.blocks.read_only": false }'


We now have a LOGSTASH_MINIMAL mode which will offload log parsing to Elasticsearch ingest node. This allows Logstash to run in as little as 200MB RAM and start instantly.


Elasticsearch ingest node parsing currently only supports standard IDS alerts and Zeek logs in JSON format.

Starting in securityonion-setup - 20120912-0ubuntu0securityonion327, LOGSTASH_MINIMAL is enabled by default for new Production Mode deployments. Evaluation Mode continues to default to traditional Logstash parsing. If you want to run Evaluation Mode with LOGSTASH_MINIMAL, you can run minimal Setup:

sudo sosetup-minimal

If you’ve already run through Setup, you can enable LOGSTASH_MINIMAL on an existing installation by adding the following to /etc/nsm/securityonion.conf:


You can then optionally decrease your Logstash heap size in /etc/logstash/jvm.options and restart Logstash:

sudo so-logstash-restart