---
title: "elasticsearch-bulk: Receive messages from Elastic clients"
url: "https://axoflow.com/docs/axosyslog-core/chapter-sources/elasticsearch-bulk/"
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).

# elasticsearch-bulk: Receive messages from Elastic clients

Available in AxoSyslog 4.28 and later.

The `elasticsearch-bulk()` source implements the [Elasticsearch Bulk API](https://www.elastic.co/docs/api/doc/elasticsearch/operation/operation-bulk). Elastic Agent, Beats, and other clients of the Bulk API can send their events to AxoSyslog by pointing their Elasticsearch output at this source, so you can process and route the events before forwarding them to Elasticsearch or to another destination.

> **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).

## Example: Receiving events from Beats

```shell
source s_es {
  elasticsearch-bulk(
    port(9200)
    auth-token("ApiKey <key>")
    version("8.15.0")
  );
};
```

Configure the Elasticsearch output of your client to point at this address, for example, in a Filebeat configuration:

```yaml
output.elasticsearch:
  hosts: ["http://<IP-of-AxoSyslog>:9200"]
  api_key: "<key>"
```

## How the messages are processed

The body of a bulk request is a sequence of action lines, each followed by a document line. AxoSyslog handles the actions as follows:

| Action | Result |
| --- | --- |
| `index`, `create` | The document line becomes a log message, and the action line is stored in `${.es_bulk.action}`. AxoSyslog acknowledges the item with status `201`. |
| `update`, `delete` | AxoSyslog skips the action and acknowledges the item with status `200`, so the client does not resend it. |
| An action without a document line | AxoSyslog rejects the item with status `400`, so the client drops a pair it could never parse instead of resending it. |

Because bulk documents are JSON and not syslog messages, this source doesn’t parse the documents as syslog. The whole document line becomes the `${MESSAGE}` of the log message.

AxoSyslog treats a request as a bulk request if its method is `POST` or `PUT`, and its path ends with `/_bulk`. It answers the requests of the clients as follows:

| Request | Response |
| --- | --- |
| A bulk request | `200 OK`, with a bulk acknowledgment body that lists the status of every item. |
| `GET /_license` | The license response that the Elastic clients expect. |
| Any other `GET` request | The version handshake, which reports the version set in [`version()`](https://axoflow.com/docs/axosyslog-core/chapter-sources/elasticsearch-bulk/index.md#version). |
| Any other request | `200 OK` |
| The [`auth-token()`](https://axoflow.com/docs/axosyslog-core/chapter-sources/elasticsearch-bulk/index.md#auth-token) option is set, and the `Authorization` header of the request is missing or doesn’t match. | `401 Unauthorized` |

Every response includes the `X-Elastic-Product: Elasticsearch` header, which the Elastic clients require.

The source accepts `gzip` and `deflate` compressed request bodies, and the [`max-request-size()`](https://axoflow.com/docs/axosyslog-core/chapter-sources/elasticsearch-bulk/index.md#max-request-size) limit applies to the decompressed body as well.

## elasticsearch-bulk() source options

The `elasticsearch-bulk()` source has the following options.

## auth-token()

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

*Description:* Requires the clients to authenticate themselves with a token. When set, AxoSyslog accepts only the requests whose `Authorization` header exactly matches the value of this option, and rejects every other request with `401 Unauthorized`.

Include the authentication scheme in the value, because AxoSyslog compares the whole header:

```shell
auth-token("Bearer s3cr3t")
```

Since the token is sent in clear text, use this option only over HTTPS, that is, together with [`transport(tls)`](https://axoflow.com/docs/axosyslog-core/chapter-sources/elasticsearch-bulk/index.md#transport).

## 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/elasticsearch-bulk/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/elasticsearch-bulk/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/elasticsearch-bulk/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() or localport()

|  |  |
| --- | --- |
| Type: | number |
| Default: | 80 for `transport(tcp)`, 443 for `transport(tls)` |

*Description:* The port number to bind to. Make sure to enable this port on the firewall of the AxoSyslog host.

## 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/elasticsearch-bulk/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.

## 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/elasticsearch-bulk/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.

## version()

|  |  |
| --- | --- |
| Type: | string |
| Default: | `8.15.0` |

*Description:* The Elasticsearch version that AxoSyslog reports to the clients in the version handshake. The Elastic clients refuse a server whose major and minor version is older than their own, unless you enable the `allow_older_versions` option on the client side. Set this option to the version your clients expect.

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