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Install Docker CE

Refer to relevant installation guides:

NOTE: READ FIRST (IPv4 forwarding)

Initial Setup

  • IMPORTANT: Always use the latest unit file (below) with the current release. By default, the latest container is automatically downloaded at each restart. Therefore, make it a habit to check back here regularly to be sure any changes that may have been made to the template unit file below (e.g. suggested mount points) are incorporated in production prior to relaunching via systemd.

  • Create the systemd unit file /lib/systemd/system/sc4s.service based on the following template:

Unit file

Description=SC4S Container
Wants=NetworkManager.service docker.service
After=NetworkManager.service docker.service



# Required mount point for syslog-ng persist data (including disk buffer)

# Optional mount point for local overrides and configurations; see notes in docs

# Optional mount point for local disk archive (EWMM output) files

# Map location of TLS custom TLS


ExecStartPre=/usr/bin/docker pull $SC4S_IMAGE

# Note: /usr/bin/bash will not be valid path for all OS
# when startup fails on running bash check if the path is correct
ExecStartPre=/usr/bin/bash -c "/usr/bin/systemctl set-environment SC4SHOST=$(hostname -s)"

ExecStart=/usr/bin/docker run \
        -e "SC4S_CONTAINER_HOST=${SC4SHOST}" \
        -v "$SC4S_PERSIST_MOUNT" \
        -v "$SC4S_LOCAL_MOUNT" \
        -v "$SC4S_ARCHIVE_MOUNT" \
        -v "$SC4S_TLS_MOUNT" \
        --env-file=/opt/sc4s/env_file \
        --network host \
        --name SC4S \
        --rm $SC4S_IMAGE

  • Execute the following command to create a local volume that will contain the disk buffer files in the event of a communication failure to the upstream destination(s). This will also be used to keep track of the state of syslog-ng between restarts, and in particular the state of the disk buffer. This is a required step.
sudo docker volume create splunk-sc4s-var
  • NOTE: Be sure to account for disk space requirements for the docker volume created above. This volume is located in /var/lib/docker/volumes/ and could grow significantly if there is an extended outage to the SC4S destinations (typically HEC endpoints). See the “SC4S Disk Buffer Configuration” section on the Configuration page for more info.

  • Create subdirectories /opt/sc4s/local /opt/sc4s/archive /opt/sc4s/tls

  • Create a file named /opt/sc4s/env_file and add the following environment variables and values:

#Uncomment the following line if using untrusted SSL certificates
  • Update SC4S_DEST_SPLUNK_HEC_DEFAULT_URL and SC4S_DEST_SPLUNK_HEC_DEFAULT_TOKEN to reflect the correct values for your environment. Do not configure HEC Acknowledgement when deploying the HEC token on the Splunk side; the underlying syslog-ng http destination does not support this feature. Moreover, HEC Ack would significantly degrade performance for streaming data such as syslog.

  • The default number of SC4S_DEST_SPLUNK_HEC_WORKERS is 10. Consult the community if you feel the number of workers (threads) should deviate from this.

  • NOTE: Splunk Connect for Syslog defaults to secure configurations. If you are not using trusted SSL certificates, be sure to uncomment the last line in the example above.

For more information about configuration refer to Docker and Podman basic configurations and detailed configuration.

Configure SC4S for systemd and start SC4S

sudo systemctl daemon-reload
sudo systemctl enable sc4s
sudo systemctl start sc4s

Restart SC4S

sudo systemctl restart sc4s

If changes were made to the configuration Unit file above (e.g. to configure with dedicated ports), you must first stop SC4S and re-run the systemd configuration commands:

sudo systemctl stop sc4s
sudo systemctl daemon-reload 
sudo systemctl enable sc4s
sudo systemctl start sc4s

Stop SC4S

sudo systemctl stop sc4s

Verify Proper Operation

SC4S has a number of “preflight” checks to ensure that the container starts properly and that the syntax of the underlying syslog-ng configuration is correct. After this step completes, to verify SC4S is properly communicating with Splunk, execute the following search in Splunk:

index=* sourcetype=sc4s:events "starting up"

This should yield an event similar to the following:

syslog-ng starting up; version='3.28.1'

When the startup process proceeds normally (without syntax errors). If you do not see this, follow the steps below before proceeding to deeper-level troubleshooting:

  • Check to see that the URL, token, and TLS/SSL settings are correct, and that the appropriate firewall ports are open (8088 or 443).
  • Check to see that the proper indexes are created in Splunk, and that the token has access to them.
  • Ensure the proper operation of the load balancer if used.
  • Lastly, execute the following command to check the sc4s startup process running in the container.
docker logs SC4S

You should see events similar to those below in the output:

syslog-ng checking config
sc4s version=v1.36.0
starting goss
starting syslog-ng

If you do not see the output above, proceed to the “Troubleshoot sc4s server” and “Troubleshoot resources” sections for more detailed information.