# Options of syslog-parser() parsers The `syslog-parser()` has the following options: ## 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](../../../docs/axosyslog-core/4.26/chapter-sources/configuring-sources-file/kernel-messages/index.md)). ## default-priority() | ---|--- Type: | priority string Default: | notice _Description:_ This parameter assigns a severity to the messages received from the source if the message does not specify one. For example, `default-priority(warning)`. ## 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()` to compute the message priority. The `default-level()` and `default-priority()` options are aliases of `default-severity()`: all three set the severity part of the message priority. If you set more than one of them, the last one takes effect. ## drop-invalid() | ---|--- Type: | yes or no Values: | `yes` or `no` Default: | no _Description:_ This option determines how the `syslog-parser()` affects messages when parsing fails. If you set `drop-invalid()` to `yes`, `syslog-parser()` will drop the message if the parsing fails. If you set `drop-invalid()` to `no`, the parsing error triggers `syslog-parser()` to rewrite and extend the original log message with the following additional information: * It prepends the following message to the contents of the `$MESSAGE` field: `Error processing log message`. * It sets the contents of the `$PROGRAM` field to `syslog-ng`. * It sets the contents of the `facility` field to `syslog`. * It sets the contents of the `severity` field to `error`. Note With the `drop-invalid(no)` option `syslog-parser()` will work in the same way as the sources which receive syslog-protocol/BSD-format messages. ### Example: enabling the drop-invalid() option Terminal window ``` parser p_syslog { syslog-parser(drop-invalid(yes)); }; ``` ## flags() | ---|--- Type: | `assume-utf8`, `check-hostname`, `check-program`, `dont-store-legacy-msghdr`, `empty-lines`, `exit-on-eof`, `expect-hostname`, `guess-timezone`, `ignore-aux-data`, `kernel`, `no-header`, `no-hostname`, `no-multi-line`, `no-parse`, `sanitize-utf8`, `store-legacy-msghdr`, `store-raw-message`, `syslog-protocol`, `validate-utf8` Default: | empty set _Description:_ Specifies the log parsing options of the source. For example: Terminal window ``` source { network(flags(check-hostname, check-program)); }; ``` ### assume-utf8 The `assume-utf8` flag assumes that the incoming messages are UTF-8 encoded, but does not verify the encoding. If you explicitly want to validate the UTF-8 encoding of the incoming message, use the `validate-utf8` flag. ### check-hostname 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 `${HOST}` field from the message. ### check-program Available in version 4.10 and later. If the `check-program` flag is enabled, AxoSyslog validates the `${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. You can also enable this behavior globally using the [`check-program` global option](../../../docs/axosyslog-core/4.26/chapter-global-options/reference-options/index.md#global-option-check-program). ### dont-store-legacy-msghdr By default, AxoSyslog stores the original incoming header of the log message. This is useful if the original format of a non-syslog-compliant message must be retained (AxoSyslog automatically corrects minor header errors, for example, adds a whitespace before `msg` in the following message: `Jan 22 10:06:11 host program:msg`). If you do not want to store the original header of the message, enable the `dont-store-legacy-msghdr` flag. ### empty-lines Use the `empty-lines` flag to keep the empty lines of the messages. By default, AxoSyslog removes empty lines automatically. ### exit-on-eof If this flag is set on a source, AxoSyslog stops when an EOF (end of file) is received. Available in version 4.9 and later. ### expect-hostname If the `expect-hostname` flag is enabled, AxoSyslog will assume that the log message contains a hostname and parse the message accordingly. This is the default behavior for TCP sources. Note that pipe sources use the `no-hostname` flag by default. ### guess-timezone Attempt to guess the timezone of the message if this information is not available in the message. Works when the incoming message stream is close to real time, and the timezone information is missing from the timestamp. ### ignore-aux-data The `ignore-aux-data` flag stops AxoSyslog from collecting the auxiliary data that the transport layer can attach to each incoming message, and from setting the related name-value pairs. Auxiliary data includes: * The UNIX credentials of the sender process on UNIX domain sockets: `${.unix.pid}`, `${.unix.uid}`, `${.unix.gid}`, `${.unix.cmdline}`, `${.unix.exe}`, `${.audit.auid}`, and `${.audit.ses}`. For details, see [UNIX credentials and other metadata](../../../docs/axosyslog-core/4.26/chapter-sources/source-unixstream/unixstream-unix-credentials/index.md). * The fields of the peer certificate on TLS-encrypted transports: `${.tls.x509_cn}`, `${.tls.x509_o}`, `${.tls.x509_ou}`, and `${.tls.x509_fp}`. * The receive timestamp and the peer address that the transport layer provides for the message. Use this flag if you do not need this metadata and want to avoid the cost of collecting it. Gathering UNIX credentials is especially expensive, because AxoSyslog reads the `/proc` filesystem for every message. ### kernel The `kernel` flag makes the source default to the `LOG_KERN | LOG_NOTICE` priority if not specified otherwise. ### no-header The `no-header` flag triggers AxoSyslog to parse only the `PRI` field of incoming messages, and put the rest of the message contents into `$MSG`. Its functionality is similar to that of the `no-parse` flag, except the `no-header` flag does not skip the `PRI` field. Note Essentially, the `no-header` flag signals AxoSyslog that the `syslog` header is not present (or does not adhere to the conventions / RFCs), so the entire message (except from the `PRI` field) is put into `$MSG`. The following example illustrates using the `no-header` flag with the `syslog-parser()` parser: Terminal window ``` parser p_syslog { syslog-parser( flags(no-header) ); }; ``` ### no-hostname Enable the `no-hostname` flag if the log message does not include the hostname of the sender host. That way AxoSyslog assumes that the first part of the message header is ${PROGRAM} instead of ${HOST}. For example: Terminal window ``` source s_dell { network( port(2000) flags(no-hostname) ); }; ``` ### no-multi-line The `no-multi-line` flag disables line-breaking in the messages: the entire message is converted to a single line. Note that this happens only if the underlying transport method actually supports multi-line messages. Currently the `file()` and `pipe()` drivers support multi-line messages. ### no-parse By default, AxoSyslog parses incoming messages as syslog messages. The `no-parse` flag completely disables syslog message parsing and processes the complete line as the message part of a syslog message. The AxoSyslog application will generate a new syslog header (timestamp, host, and so on) automatically and put the entire incoming message into the MESSAGE part of the syslog message (available using the `${MESSAGE}` macro). This flag is useful for parsing messages not complying to the syslog format. If you are using the `flags(no-parse)` option, then syslog message parsing is completely disabled, and the entire incoming message is treated as the ${MESSAGE} part of a syslog message. In this case, AxoSyslog generates a new syslog header (timestamp, host, and so on) automatically. Note that even though `flags(no-parse)` disables message parsing, some flags can still be used, for example, the `no-multi-line` flag. ### sanitize-utf8 When using the `sanitize-utf8` flag, AxoSyslog converts non-UTF-8 input to an escaped form, which is valid UTF-8. Prior to version 4.6, this flag worked only when parsing RFC3164 messages. Starting with version 4.6, it works also for RFC5424 and raw messages. ### store-legacy-msghdr By default, AxoSyslog stores the original incoming header of the log message, so this flag is active. To disable it, use the `dont-store-legacy-msghdr` flag. ### store-raw-message Save the original message as received from the client in the `${RAWMSG}` macro. You can forward this raw message in its original form to another AxoSyslog node using the [`syslog-ng()` destination](../../../docs/axosyslog-core/4.26/chapter-destinations/destination-syslog-ng/index.md), or to a SIEM system, ensuring that the SIEM can process it. Available only in 3.16 and later. ### syslog-protocol The `syslog-protocol` flag specifies that incoming messages are expected to be formatted according to the new IETF syslog protocol standard (RFC5424), but without the frame header. Note that this flag is not needed for the `syslog` driver, which handles only messages that have a frame header. ### validate-utf8 The `validate-utf8` flag enables encoding-verification for messages. Prior to version 4.6, this flag worked only when parsing RFC3164 messages. Starting with version 4.6, it works also for RFC5424 and raw messages. For RFC5424-formatted messages, if the BOM character is missing, but the message is otherwise UTF-8 compliant, AxoSyslog automatically adds the BOM character to the message. The byte order mark (BOM) is a Unicode character used to signal the byte-order of the message text. For the `syslog-parser()` you can also set the following flags: * `check-hostname`: Equivalent with the [`check-hostname()` global option](../../../docs/axosyslog-core/4.26/chapter-global-options/reference-options/index.md#global-option-check-hostname), but only applies to this parser. * `no-piggyback-errors`: Do not attribute the message to AxoSyslog in case of errors. Things already processed or extracted are retained, for example: `${MESSAGE}` retains its value (potentially the raw message), other macros like `${HOST}`, `${PROGRAM}`, or `${PID}` may or may not be extracted. The error is indicated by setting `${MSGFORMAT}` set to “syslog:error”. Available in AxoSyslog 4.8.1 and later. ## internal() | ---|--- Accepted values: | `yes`, `no` Default: | `no` _Description:_ Marks this pipeline element as internal. Elements marked as `internal()` are treated as an implementation detail, so for example statistics of the given pipe are available only on higher stats level. This option is mainly useful for developers or when writing SCL blocks and integrations. ## sdata-prefix() | ---|--- Type: | string Default: | `.SDATA.` Available in AxoSyslog 4.1 and later. _Description:_ Adds a specific string before the names of the parsed SDATA fields to store the name-value pairs created from the SDATA fields separately. Note that unless the value of `sdata-prefix` starts with `.SDATA.`, using this option excludes the parsed fields from the [`sdata` and `rfc5424` scopes of the value pairs](../../../docs/axosyslog-core/4.26/chapter-concepts/concepts-value-pairs/option-value-pairs/index.md#scope). ## template() | ---|--- Synopsis: | `template("${}")` _Description:_ The macro that contains the part of the message that the parser will process. It can also be a macro created by a previous parser of the log path. By default, the parser processes the entire message (`${MESSAGE}`). ## 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. Last modified August 6, 2026: [Sync syslog parser with source code (3a8db7db)]()