---
title: "splunk-hec: Receive messages from Splunk HEC clients"
url: "https://axoflow.com/docs/axosyslog-core/chapter-sources/splunk-hec/"
last_modified: "2026-09-25T11:41:50+02:00"
---

> For the complete documentation index, see [llms.txt](https://axoflow.com/docs/axosyslog-core/llms.txt).

# splunk-hec: Receive messages from Splunk HEC clients

Available in AxoSyslog 4.28 and later.

The `splunk-hec()` source receives messages from clients that send data to the [Splunk HTTP Event Collector (HEC)](https://docs.splunk.com/Documentation/Splunk/latest/Data/UsetheHTTPEventCollector), for example, from [Splunk Connect for Syslog (SC4S)](https://splunk.github.io/splunk-connect-for-syslog/main/destinations/). This way you can point your existing HEC clients at AxoSyslog without reconfiguring them, and process or route the messages before forwarding them to Splunk or to another destination.

To send messages to Splunk, use the [`splunk-hec-event()` destination](https://axoflow.com/docs/axosyslog-core/chapter-destinations/syslog-ng-with-splunk/index.md) instead.

> **Note:**
> This driver is a reusable configuration snippet. For details on such configuration snippets, see [Reusing configuration blocks](https://axoflow.com/docs/axosyslog-core/chapter-configuration-file/large-configs/config-blocks/index.md).

## Prerequisites

- Include the AxoSyslog configuration library in your configuration file: `@include "scl.conf"`
- Install the `http` and `json` modules: the `axosyslog-mod-http` and `axosyslog-mod-json` packages on Debian and derivatives, or the `axosyslog-http` and `axosyslog-json` packages on RHEL and derivatives.

## Example: Receiving HEC events

Minimal configuration:

```shell
@include "scl.conf"

source s_splunk_hec {
  splunk-hec(
    token("a1b2c3d4-e5f6-4a7b-8c9d-0e1f2a3b4c5d")
  );
};
```

To receive the events over HTTPS, configure TLS:

```shell
source s_splunk_hec_tls {
  splunk-hec(
    token("a1b2c3d4-e5f6-4a7b-8c9d-0e1f2a3b4c5d")
    transport(tls)
    tls(
      key-file("/etc/syslog-ng/hec.key")
      cert-file("/etc/syslog-ng/hec.crt")
    )
  );
};
```

To test the source, you can use `curl` on the host where AxoSyslog is running:

```shell
curl -X POST -H "Authorization: Splunk a1b2c3d4-e5f6-4a7b-8c9d-0e1f2a3b4c5d" \
  --data '{"time": 1757000000.000, "host": "example-host", "event": "hello from HEC"}' \
  http://127.0.0.1:8088/services/collector
```

AxoSyslog accepts the request and answers it with the response the HEC clients expect:

```json
{"text":"Success","code":0}
```

## How the messages are processed

The `splunk-hec()` source handles the incoming requests as follows:

1. It authenticates the request: the `Authorization` header must be `Splunk <token>`, where `<token>` is the value of the [`token()`](https://axoflow.com/docs/axosyslog-core/chapter-sources/splunk-hec/index.md#token) option. AxoSyslog rejects every other request with `401 Unauthorized`.
2. It extracts the events from the body of the request. A request can contain a JSON array of events, or several concatenated JSON objects, and each event becomes a separate log message.
3. It parses each event with the [`json-parser()`](https://axoflow.com/docs/axosyslog-core/chapter-parsers/json-parser/index.md), and makes the fields available with the prefix set in the [`prefix()`](https://axoflow.com/docs/axosyslog-core/chapter-sources/splunk-hec/index.md#prefix) option, for example, `${.splunk.source}` and `${.splunk.sourcetype}`.
4. It maps the standard HEC fields to AxoSyslog macros:

   | HEC field | Macro |
   | --- | --- |
   | `event` | `${MESSAGE}` |
   | `host` | `${HOST}` |
   | `time` | The timestamp of the message. AxoSyslog accepts both the `<seconds>.<milliseconds>` and the `<seconds>` epoch formats. |

   AxoSyslog maps a field only if it is present and not empty, otherwise the macro keeps its original value.
5. If the payload is not valid JSON, AxoSyslog parses it as a syslog message instead. This way the source also accepts the raw endpoint of HEC.

The source accepts `gzip` and `deflate` compressed request bodies.

## splunk-hec() source options

The `splunk-hec()` source has the following options.

> **Note:**
> The `splunk-hec()` source sets the `mode()`, `auth-token()`, `response-body()`, and `flags()` options of the underlying [`ehttp()` source](https://axoflow.com/docs/axosyslog-core/chapter-sources/ehttp/index.md). Set the [`token()`](https://axoflow.com/docs/axosyslog-core/chapter-sources/splunk-hec/index.md#token) option instead of `auth-token()`. Setting `mode()` or `response-body()` overrides the value the driver uses and breaks compatibility with the HEC clients.

## chain-hostnames()

|  |  |
| --- | --- |
| Accepted values: | `yes`, `no` |
| Default: | `no` |

*Description:* Enable or disable the chained hostname format. For details, see the [chain-hostnames() global option](https://axoflow.com/docs/axosyslog-core/chapter-global-options/reference-options/index.md#global-options-chain-hostnames).

## check-hostname()

|  |  |
| --- | --- |
| Type: | boolean (`yes` or `no`) |
| Default: | Use the global `check-hostname()` option, which defaults to `no`. |

*Description:*

When receiving messages, AxoSyslog can check whether the hostname contains valid characters.

Valid characters are:

- alphanumeric characters (A-Z, a-z, 0-9)
- the dash (`-`) and underscore (`_`) characters
- the dot (`.`) and the colon (`:`) characters
- the `@` and slash (`/`)

If the hostname contains invalid characters, AxoSyslog sets the `syslog.invalid_hostname` tag for the message, and doesn’t parse the `${HOST}` field from the message.

Uses the value of the [global option](https://axoflow.com/docs/axosyslog-core/chapter-global-options/reference-options/index.md#global-option-check-hostname) if not specified.

## check-program()

|  |  |
| --- | --- |
| Type: | yes or no |
| Default: | no |

*Description:*

Available in version 4.10 and later.

If the `check-program` flag is enabled, AxoSyslog validates the `${PROGRAM}` field for RFC3164-formatted messages. Valid program names meet the following criteria:

- Contain only these characters: `[a-zA-Z0-9-_/().]`
- Include at least one alphabetical character.

If the program name fails validation, it’s considered to be part of the log message.

## default-facility()

|  |  |
| --- | --- |
| Type: | facility string |
| Default: | user |

*Description:* This parameter assigns a facility value to the messages received from the source if the message does not specify one. The default is `user` (`kern` for [kernel sources](https://axoflow.com/docs/axosyslog-core/chapter-sources/configuring-sources-file/kernel-messages/index.md)).

## default-severity()

|  |  |
| --- | --- |
| Type: | severity string |
| Default: | `notice` |

*Description:* Assigns a default severity to messages received from this source when the message doesn’t specify one. Accepts the standard syslog severity keywords (for example, `emerg`, `alert`, `crit`, `err`, `warning`, `notice`, `info`, `debug`). Combined with [`default-facility()`](https://axoflow.com/docs/axosyslog-core/chapter-sources/splunk-hec/index.md#default-facility) to compute the message priority.

## dns-cache()

|  |  |
| --- | --- |
| Accepted values: | `yes`, `no` |
| Default: | `no` |

*Description:* Enable or disable DNS cache usage.

## host-override()

|  |  |
| --- | --- |
| Type: | string |
| Default: |  |

*Description:* Replaces the ${HOST} part of the message with the parameter string.

## idle-timeout()

|  |  |
| --- | --- |
| Accepted values: | number [seconds] |
| Default: | `0` (disabled) |

Available in AxoSyslog 4.9 and later.

If set, AxoSyslog closes the client connection if no data is received for the specified amount of time (in seconds).

## internal()

|  |  |
| --- | --- |
| Accepted values: | `yes`, `no` |
| Default: | `no` |

*Description:* Marks this pipeline element as internal. Elements marked as `internal()` are treated as an implementation detail, so for example statistics of the given pipe are available only on higher stats level. This option is mainly useful for developers or when writing SCL blocks and integrations.

## ip() or localip()

|  |  |
| --- | --- |
| Type: | string |
| Default: | `0.0.0.0` |

*Description:* The IP address to bind to. By default, AxoSyslog listens on every available interface. Note that this is not the address where messages are accepted from.

## ip-freebind()

|  |  |
| --- | --- |
| Type: | yes or no |
| Default: | no |

*Description:* Linux-only. Enables the `IP_FREEBIND` socket option, allowing AxoSyslog to bind to a non-local IP address. Useful when the address isn’t yet configured on any interface (for example, during failover scenarios) so the source can listen before the address becomes available. Has no effect on platforms that don’t support `IP_FREEBIND`.

## ip-protocol()

|  |  |
| --- | --- |
| Type: | number |
| Default: | 4 |

*Description:* Determines the internet protocol version of the given driver (`network()` or `syslog()`). The possible values are `4` and `6`, corresponding to IPv4 and IPv6. The default value is `ip-protocol(4)`.

Note that listening on a port using IPv6 automatically means that you are also listening on that port using IPv4. That is, if you want to have receive messages on an IP-address/port pair using both IPv4 and IPv6, create a source that uses the `ip-protocol(6)`. You cannot have two sources with the same IP-address/port pair, but with different `ip-protocol()` settings (it causes an `Address already in use` error).

For example, the following source receives messages on TCP, using the `network()` driver, on every available interface of the host on both IPv4 and IPv6.

```shell
source s_network_tcp { network( transport("tcp") ip("::") ip-protocol(6) port(601) ); };
```

## ip-tos()

|  |  |
| --- | --- |
| Type: | number |
| Default: | 0 |

*Description:* Specifies the Type-of-Service value of outgoing packets.

## ip-ttl()

|  |  |
| --- | --- |
| Type: | number |
| Default: | 0 |

*Description:* Specifies the Time-To-Live value of outgoing packets.

## keep-alive()

|  |  |
| --- | --- |
| Type: | yes or no |
| Default: | yes |

*Description:* Specifies whether connections to sources should be closed when AxoSyslog is forced to reload its configuration (upon the receipt of a SIGHUP signal). Note that this applies to the server (source) side of the AxoSyslog connections, client-side (destination) connections are always reopened after receiving a HUP signal unless the `keep-alive` option is enabled for the destination.

## keep-hostname()

|  |  |
| --- | --- |
| Type: | yes or no |
| Default: | no |

*Description:* Enable or disable hostname rewriting.

- If enabled (`keep-hostname(yes)`), AxoSyslog assumes that the incoming log message was sent by the host specified in the `HOST` field of the message.
- If disabled (`keep-hostname(no)`), AxoSyslog rewrites the `HOST` field of the message, either to the IP address (if the `use-dns()` parameter is set to `no`), or to the hostname (if the `use-dns()` parameter is set to `yes` and the IP address can be resolved to a hostname) of the host sending the message to AxoSyslog. For details on using name resolution in AxoSyslog, see [Using name resolution in syslog-ng](https://axoflow.com/docs/axosyslog-core/chapter-examples/examples-dns/index.md).

> **Note:**
>
> If the log message does not contain a hostname in its `HOST` field, AxoSyslog automatically adds a hostname to the message.
>
> - For messages received from the network, this hostname is the address of the host that sent the message (this means the address of the last hop if the message was transferred via a relay).
> - For messages received from the local host, AxoSyslog adds the name of the host.

This option can be specified globally, and per-source as well. The local setting of the source overrides the global option if available.

> **Note:**
> When relaying messages, enable this option on the AxoSyslog server and also on every relay, otherwise AxoSyslog will treat incoming messages as if they were sent by the last relay.

## keep-timestamp()

|  |  |
| --- | --- |
| Type: | yes or no |
| Default: | yes |

*Description:* Specifies whether AxoSyslog should accept the timestamp received from the sending application or client. If disabled, the time of reception will be used instead. This option can be specified globally, and per-source as well. The local setting of the source overrides the global option if available.

> **Warning:**
> To use the `S_` macros, the `keep-timestamp()` option must be enabled (this is the default behavior of AxoSyslog).

## listen-backlog()

|  |  |
| --- | --- |
| Type: | integer |
| Default: | 256 |

*Description:* Available only for stream based transports (`unix-stream`, `tcp`, `tls`). In TCP, connections are treated incomplete until the three-way handshake is completed between the server and the client. Incomplete connection requests wait on the TCP port for the listener to accept the request. The `listen-backlog()` option sets the maximum number of incomplete connection requests. For example:

```shell
   source s_network {
        network(
            ip("192.168.1.1")
            transport("tcp")
            listen-backlog(2048)
            );
    };
```

## log-fetch-limit()

|  |  |
| --- | --- |
| Type: | number |
| Default: | 100 |

*Description:* The maximum number of messages fetched from a source during a single poll loop. The destination queues might fill up before flow-control could stop reading if `log-fetch-limit()` is too high.

## log-iw-size()

|  |  |
| --- | --- |
| Type: | number |
| Default: | The value of [`max-connections()`](https://axoflow.com/docs/axosyslog-core/chapter-sources/splunk-hec/index.md#max-connections) multiplied by [`min-iw-size-per-reader()`](https://axoflow.com/docs/axosyslog-core/chapter-global-options/reference-options/index.md#global-option-min-iw-size-per-reader) |

*Description:* The size of the source window, that is, the maximum number of in-flight messages the source permits before flow control is enforced. This applies only when `flags(flow-control)` is set. For details, see [Managing incoming and outgoing messages with flow-control](https://axoflow.com/docs/axosyslog-core/chapter-routing-filters/concepts-flow-control/index.md).

## log-msg-size()

|  |  |
| --- | --- |
| Type: | number (bytes) |
| Default: | Use the global `log-msg-size()` option, which defaults to `65536` (64 KiB). |

*Description:* Maximum length of an incoming message in bytes. This length includes the entire message (the data structure and individual fields). The maximal value that can be set is 268435456 bytes (256 MiB).

For messages using the IETF-syslog message format (RFC5424), the maximal size of the value of an SDATA field is 64 KiB.

> **Note:**
> In most cases, `log-msg-size()` does not need to be set higher than 10 MiB.

For details on how encoding affects the size of the message, see [Message size and encoding](https://axoflow.com/docs/axosyslog-core/chapter-concepts/concepts-message-representation/index.md).

You can use human-readable units when setting configuration options. For details, see[Notes about the configuration syntax](https://axoflow.com/docs/axosyslog-core/chapter-configuration-file/configuration-syntax-notes/index.md).

Uses the value of the [global option](https://axoflow.com/docs/axosyslog-core/chapter-global-options/reference-options/index.md#global-option-log-msg-size) if not specified.

## log-prefix() (DEPRECATED)

|  |  |
| --- | --- |
| Type: | string |
| Default: |  |

This option is deprecated. Use `program-override` instead.

*Description:* A string added to the beginning of every log message. It can be used to add an arbitrary string to any log source, though it is most commonly used for adding `kernel:` to the kernel messages on Linux.

## max-connections()

|  |  |
| --- | --- |
| Type: | number |
| Default: | 100 |

*Description:* The maximum number of simultaneous client connections that the source accepts.

## max-request-size()

|  |  |
| --- | --- |
| Type: | number [bytes] |
| Default: | The value of [`log-msg-size()`](https://axoflow.com/docs/axosyslog-core/chapter-sources/splunk-hec/index.md#log-msg-size) multiplied by 1000 |

*Description:* The maximum size of a single HTTP request, in bytes. AxoSyslog rejects larger requests with `413 Payload Too Large` and logs an error.

For compressed requests, this limit applies to the decompressed body as well.

## normalize-hostnames()

|  |  |
| --- | --- |
| Accepted values: | `yes`, `no` |
| Default: | `no` |

*Description:* If enabled (`normalize-hostnames(yes)`), AxoSyslog converts the hostnames to lowercase.

> **Note:**
> This setting applies only to hostnames resolved from DNS. It has no effect if the `keep-hostname()` option is enabled, and the message contains a hostname.

## persist-name()

|  |  |
| --- | --- |
| Type: | string |
| Default: | N/A |

*Description:* If you receive the following error message during AxoSyslog startup, set the `persist-name()` option of the duplicate drivers:

```shell
Error checking the uniqueness of the persist names, please override it with persist-name option. Shutting down.
```

This error happens if you use identical drivers in multiple sources, for example, if you configure two file sources to read from the same file. In this case, set the `persist-name()` of the drivers to a custom string, for example, `persist-name("example-persist-name1")`.

## port()

|  |  |
| --- | --- |
| Type: | number |
| Default: | 8088 |

*Description:* The port number to bind to. The default is the default port of the Splunk HTTP Event Collector. Setting [`transport(tls)`](https://axoflow.com/docs/axosyslog-core/chapter-sources/splunk-hec/index.md#transport) doesn’t change this default. Make sure to enable this port on the firewall of the AxoSyslog host.

## prefix()

|  |  |
| --- | --- |
| Type: | string |
| Default: | `.splunk.` |

*Description:* The prefix that AxoSyslog inserts before the name of the fields parsed from the event, to avoid collisions with other name-value pairs of the message. For example, with the default prefix, the `sourcetype` field of the event becomes available as `${.splunk.sourcetype}`.

Names starting with a dot (for example, `.example`) are reserved for use by AxoSyslog. If you use such a macro name as the name of a parsed value, it will attempt to replace the original value of the macro (note that only soft macros can be overwritten, see [Hard versus soft macros](https://axoflow.com/docs/axosyslog-core/chapter-manipulating-messages/customizing-message-format/macros-hard-vs-soft/index.md) for details). To avoid such problems, use a prefix when naming the parsed values, for example, `prefix(my-parsed-data.)`

## program-override()

|  |  |
| --- | --- |
| Type: | string |
| Default: |  |

*Description:* Replaces the ${PROGRAM} part of the message with the parameter string. For example, to mark every message coming from the kernel, include the `program-override("kernel")` option in the source containing `/proc/kmsg`.

## read-old-records()

|  |  |
| --- | --- |
| Type: | `yes` or `no` |
| Default: | yes |

*Description:* If set to `yes`, AxoSyslog will start reading the records from the beginning of the file/journal, if the file/journal has not been read yet. If set to `no`, AxoSyslog will read only the new records. If the source has a state in the persist file, this option will have no effect.

## sdata-prefix()

|  |  |
| --- | --- |
| Type: | string |
| Default: | `.SDATA.` |

Available in AxoSyslog 4.1 and later.

*Description:* Adds a specific string before the names of the parsed SDATA fields to store the name-value pairs created from the SDATA fields separately. Note that unless the value of `sdata-prefix` starts with `.SDATA.`, using this option excludes the parsed fields from the [`sdata` and `rfc5424` scopes of the value pairs](https://axoflow.com/docs/axosyslog-core/chapter-concepts/concepts-value-pairs/option-value-pairs/index.md#scope).

## so-broadcast()

|  |  |
| --- | --- |
| Type: | yes or no |
| Default: | no |

*Description:* This option controls the `SO_BROADCAST` socket option required to make AxoSyslog send messages to a broadcast address. For details, see the `socket(7)` manual page.

## so-keepalive()

|  |  |
| --- | --- |
| Type: | yes or no |
| Default: | no |

*Description:* Enables keep-alive messages, keeping the socket open. This only effects TCP and UNIX-stream sockets. For details, see the `socket(7)` manual page.

## so-rcvbuf()

|  |  |
| --- | --- |
| Type: | number |
| Default: | 0 |

*Description:* Specifies the size of the socket receive buffer in bytes. For details, see the `socket(7)` manual page.

> **Warning:**
>
> When receiving messages using the UDP protocol, increase the size of the UDP receive buffer on the receiver host (that is, the AxoSyslog server or relay receiving the messages). Note that on certain platforms, for example, on Red Hat Enterprise Linux 5, even low message load (~200 messages per second) can result in message loss, unless the `so-rcvbuf()` option of the source is increased. In this cases, you will need to increase the `net.core.rmem_max` parameter of the host (for example, to `1024000`), but do not modify `net.core.rmem_default` parameter.
>
> As a general rule, increase the `so-rcvbuf()` so that the buffer size in kilobytes is higher than the rate of incoming messages per second. For example, to receive 2000 messages per second, set the `so-rcvbuf()` at least to `2 097 152` bytes.

## so-sndbuf()

|  |  |
| --- | --- |
| Type: | number |
| Default: | 0 |

*Description:* Specifies the size of the socket send buffer in bytes. For details, see the `socket(7)` manual page.

## tags()

|  |  |
| --- | --- |
| Type: | string |
| Default: |  |

*Description:* Label the messages received from the source with custom tags. Tags must be unique, and enclosed between double quotes. When adding multiple tags, separate them with comma, for example, `tags("dmz", "router")`. This option is available only in version 3.1 and later.

## tcp-keepalive-intvl()

|  |  |
| --- | --- |
| Type: | number [seconds] |
| Default: | 0 |

*Description:* Specifies the interval (number of seconds) between subsequent keepalive probes, regardless of the traffic exchanged in the connection. This option is equivalent to `/proc/sys/net/ipv4/tcp_keepalive_intvl`. The default value is `0`, which means using the kernel default.

> **Warning:**
>
> The `tcp-keepalive-time()`, `tcp-keepalive-probes()`, and `tcp-keepalive-intvl()` options only work on platforms which support the `TCP_KEEPCNT`, `TCP_KEEPIDLE`,and `TCP_KEEPINTVL` setsockopts. Currently, this is Linux.
>
> A connection that has no traffic is closed after `tcp-keepalive-time() + tcp-keepalive-intvl() * tcp-keepalive-probes()` seconds.

Available in AxoSyslog version 3.4 and later.

## tcp-keepalive-probes()

|  |  |
| --- | --- |
| Type: | number |
| Default: | 0 |

*Description:* Specifies the number of unacknowledged probes to send before considering the connection dead. This option is equivalent to `/proc/sys/net/ipv4/tcp_keepalive_probes`. The default value is `0`, which means using the kernel default.

> **Warning:**
>
> The `tcp-keepalive-time()`, `tcp-keepalive-probes()`, and `tcp-keepalive-intvl()` options only work on platforms which support the `TCP_KEEPCNT`, `TCP_KEEPIDLE`,and `TCP_KEEPINTVL` setsockopts. Currently, this is Linux.
>
> A connection that has no traffic is closed after `tcp-keepalive-time() + tcp-keepalive-intvl() * tcp-keepalive-probes()` seconds.

Available in AxoSyslog version 3.4 and later.

## tcp-keepalive-time()

|  |  |
| --- | --- |
| Type: | number [seconds] |
| Default: | 0 |

*Description:* Specifies the interval (in seconds) between the last data packet sent and the first keepalive probe. This option is equivalent to `/proc/sys/net/ipv4/tcp_keepalive_time`. The default value is `0`, which means using the kernel default.

> **Warning:**
>
> The `tcp-keepalive-time()`, `tcp-keepalive-probes()`, and `tcp-keepalive-intvl()` options only work on platforms which support the `TCP_KEEPCNT`, `TCP_KEEPIDLE`,and `TCP_KEEPINTVL` setsockopts. Currently, this is Linux.
>
> A connection that has no traffic is closed after `tcp-keepalive-time() + tcp-keepalive-intvl() * tcp-keepalive-probes()` seconds.

Available in AxoSyslog version 3.4 and later.

## time-zone()

|  |  |
| --- | --- |
| Type: | name of the timezone, or the timezone offset |
| Default: |  |

*Description:* The default timezone for messages read from the source. Applies only if no timezone is specified within the message itself.

The timezone can be specified by using the name, for example, `time-zone("Europe/Budapest")`), or as the timezone offset in +/-HH:MM format, for example, `+01:00`). On Linux and UNIX platforms, the valid timezone names are listed under the `/usr/share/zoneinfo` directory.

## tls()

|  |  |
| --- | --- |
| Type: | TLS options |
| Default: |  |

*Description:* The TLS settings of the source, for example, the certificate and the private key that AxoSyslog shows to the clients. Setting [`transport(tls)`](https://axoflow.com/docs/axosyslog-core/chapter-sources/splunk-hec/index.md#transport) requires a `tls()` block. For details on the individual options, see [TLS options](https://axoflow.com/docs/axosyslog-core/chapter-encrypted-transport-tls/tlsoptions/index.md).

```shell
tls(
    key-file("/etc/syslog-ng/server.key")
    cert-file("/etc/syslog-ng/server.crt")
)
```

The following TLS options are available: `ca-dir()`, `cert-file()`, `cipher-suite()`, `crl-dir()`, `dhparam-file()`, `ecdh-curve-list()`, `key-file()`, `peer-verify()`, `pkcs12-file()`, `ssl-options()`, `trusted-dn()`, and `trusted-keys()`.

> **Note:**
> This is a narrower set than what the `network()` and `syslog()` sources accept. In particular, `ca-file()` is not available, use `ca-dir()` instead. The `trusted-fingerprints()`, `ocsp-stapling-verify()`, `sigalgs()`, and `keylog-file()` options are not available either.

## token()

|  |  |
| --- | --- |
| Type: | string |
| Default: |  |

*Description:* The HEC token that the clients must send in the `Authorization` header of their requests. This is the token that you would otherwise configure on your Splunk deployment, so you can reuse the token your clients already have.

This option is mandatory: if you don’t set it, AxoSyslog rejects every request. Since the token is sent in clear text, use [`transport(tls)`](https://axoflow.com/docs/axosyslog-core/chapter-sources/splunk-hec/index.md#transport) to receive the events over HTTPS.

## transport()

|  |  |
| --- | --- |
| Type: | `tcp` or `tls` |
| Default: | `tcp` |

*Description:* Sets whether the source accepts plain HTTP (`tcp`) or HTTPS (`tls`) connections. Setting `transport(tls)` requires a [`tls()`](https://axoflow.com/docs/axosyslog-core/chapter-sources/splunk-hec/index.md#tls) block, and changes the default port to 443.

## use-dns()

|  |  |
| --- | --- |
| Type: | `yes`, `no`, `persist_only` |
| Default: | `yes` |

*Description:* Enable or disable DNS usage. The `persist_only` option attempts to resolve hostnames locally from a file (for example, from `/etc/hosts`) set using the [`dns-cache-hosts()` global option](https://axoflow.com/docs/axosyslog-core/chapter-global-options/reference-options/index.md#global-option-dns-cache-hosts). The AxoSyslog application blocks on DNS queries, so enabling DNS may lead to a Denial of Service attack. To prevent DoS, protect your AxoSyslog network endpoint with firewall rules, and make sure that all hosts which may get to AxoSyslog are resolvable. This option can be specified globally, and per-source as well. The local setting of the source overrides the global option if available.

For details on configuring local DNS resolution, see [Using name resolution in syslog-ng](https://axoflow.com/docs/axosyslog-core/chapter-examples/examples-dns/index.md).

> **Note:**
> This option has no effect if the `keep-hostname()` option is enabled (`keep-hostname(yes)`) and the message contains a hostname.

## use-fqdn()

|  |  |
| --- | --- |
| Type: | yes or no |
| Default: | no |

*Description:* Use this option to add a Fully Qualified Domain Name (FQDN) instead of a short hostname. You can specify this option either globally or per-source. The local setting of the source overrides the global option if available.

> **Note:**
> Set `use-fqdn()` to `yes` if you want to use the `custom-domain()` global option.

> **Note:**
> This option has no effect if the `keep-hostname()` option is enabled (`keep-hostname(yes)`) and the message contains a hostname.

## use-syslogng-pid()

|  |  |
| --- | --- |
| Type: | `yes`, `no` |
| Default: | `no` |

*Description:* When enabled, AxoSyslog overrides the PID from the original message with the PID of the `syslog-ng` process.

Last modified September 25, 2026: [Small fixes from Anno's review (8731bc10)](https://github.com/axoflow/axosyslog-core-docs/commit/8731bc10e0cb083b577d8792a883b5d65760f838)