Global options reference

The following options can be specified in the options statement, as described in Configuring global options.

bad-hostname()

Description: A regexp containing hostnames which should not be handled as hostnames.

chain-hostnames()

Description: Enable or disable the chained hostname format. If a client sends the log message directly to the AxoSyslog server, the chain-hostnames() option is enabled on the server, and the client sends a hostname in the message that is different from its DNS hostname (as resolved from DNS by the AxoSyslog server), then the server can append the resolved hostname to the hostname in the message (separated with a / character) when the message is written to the destination.

For example, consider a client-server scenario with the following hostnames: client-hostname-from-the-message, client-hostname-resolved-on-the-server, server-hostname. The hostname of the log message written to the destination depends on the keep-hostname() and the chain-hostnames() options. How keep-hostname() and chain-hostnames() options are related is described in the following table.

If the log message is forwarded to the AxoSyslog server via a AxoSyslog relay, the hostname depends on the settings of the keep-hostname() and the chain-hostnames() options both on the AxoSyslog relay and the AxoSyslog server.

For example, consider a client-relay-server scenario with the following hostnames: client-hostname-from-the-message, client-hostname-resolved-on-the-relay, client-hostname-resolved-on-the-server, relay-hostname-resolved-on-the-server. How keep-hostname() and chain-hostnames() options are related is described in the following table.

The chain-hostnames() option can interfere with the way AxoSyslog counts the log source hosts. As a result, AxoSyslog falsely perceives several hosts logging to the central server, especially if the clients sends a hostname in the message that is different from its real hostname (as resolved from DNS). Disable the chain-hostnames() option on your log sources to avoid any problems related to license counting.

check-hostname()

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.

The check-hostname() global option applies to the following sources: file(), network(), pipe(), program(), stdin(), syslog(), systemd-syslog(), unix-dgram(), unix-stream(), wildcard-file(). Instead of using the global option, you can also set the check-hostname() option for the specific source.

For the python() and python-fetcher() sources and the syslog-parser() parser you can enable this option as a flag.

create-dirs()

Description: Enable or disable directory creation for destination files and sockets.

custom-domain()

Description: Use this option to specify a custom domain name that is appended after the short hostname to receive the fully qualified domain name (FQDN). This option affects every outgoing message: eventlog sources, file sources, MARK messages and internal messages of AxoSyslog.

• If the hostname is a short hostname, the custom domain name is appended after the hostname (for example, mypc becomes mypc.customcompany.local).

• If the hostname is an FQDN, the domain name part is replaced with the custom domain name (for example, if the FQDN in the forwarded message is mypc.mycompany.local and the custom domain name is customcompany.local, the hostname in the outgoing message becomes mypc.customcompany.local).

dir-group()

Description: The default group for newly created directories.

dir-owner()

Description: The default owner of newly created directories.

dir-perm()

Description: The permission mask of directories created by syslog-ng. Log directories are only created if a file after macro expansion refers to a non-existing directory, and directory creation is enabled (see also the create-dirs() option). For octal numbers prefix the number with 0, for example, use 0755 for rwxr-xr-x.

To preserve the original properties of an existing directory, use the option without specifying an attribute: dir-perm(). Note that when creating a new directory without specifying attributes for dir-perm(), the default permission of the directories is masked with the umask of the parent process (typically 0022).

Starting with version 3.16, the default value of this option is -1, so AxoSyslog does not change the ownership, unless explicitly configured to do so.

dns-cache()

Description: Enable or disable DNS cache usage.

dns-cache-expire()

Description: Number of seconds while a successful lookup is cached.

dns-cache-expire-failed()

Description: Number of seconds while a failed lookup is cached.

dns-cache-hosts()

Description: Name of a file in /etc/hosts format that contains static IP->hostname mappings. Use this option to resolve hostnames locally without using a DNS. Note that any change to this file triggers a reload in syslog-ng and is instantaneous.

dns-cache-size()

Description: Number of hostnames in the DNS cache.

file-template()

Description: Specifies a template that file-like destinations use by default. For example:

   template t_isostamp { template("$ISODATE $HOST $MSGHDR$MSG\n"); };
    
    options { file-template(t_isostamp); };

flush-lines()

Description: Specifies how many lines are flushed to a destination at a time. The AxoSyslog application waits for this number of lines to accumulate and sends them off in a single batch. Increasing this number increases throughput as more messages are sent in a single batch, but also increases message latency.

The AxoSyslog application flushes the messages if it has sent flush-lines() number of messages, or the queue became empty. If you stop or reload AxoSyslog or in case of network sources, the connection with the client is closed, AxoSyslog automatically sends the unsent messages to the destination.

frac-digits()

Description: The AxoSyslog application can store fractions of a second in the timestamps according to the ISO8601 format. The frac-digits() parameter specifies the number of digits stored. The digits storing the fractions are padded by zeros if the original timestamp of the message specifies only seconds. Fractions can always be stored for the time the message was received.

group()

Description: The default group of output files. By default, syslog-ng changes the privileges of accessed files (for example, /dev/null) to root.root 0600. To disable modifying privileges, use this option with the -1 value.

jvm-options()

Description: Specify the Java Virtual Machine (JVM) settings of your Java destination from the AxoSyslog configuration file.

For example:

   jvm-options("-Xss1M -XX:+TraceClassLoading")

keep-hostname()

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.

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

keep-timestamp()

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.

log-fifo-size()

Description: The number of messages that the output queue can store.

log-level()

Description: Controls AxoSyslog’s own internal log level. Corresponds to setting the internal log level using syslog-ng-ctl or the command line options of syslog-ng (the -d, -v, and -t ). Setting the log level in the configuration makes it easier to control logging in containerized environments where changing command line options is more problematic.

Available in AxoSyslog 4.0 and later.

Higher log-levels automatically include messages from lower log-levels:

• default: Just normal log messages.
• verbose: Normal and verbose log messages.
• debug: Include debug messages of AxoSyslog.
• trace: Include trace messages of how messages are processed.

    options {
      log-level(debug);
    };

log-msg-size()

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.

In most cases, <code>log-msg-size()</code> 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.

You can use human-readable units when setting configuration options. For details, seeNotes about the configuration syntax.

mark() (DEPRECATED)

Description: The mark-freq() option is an alias for the deprecated mark() option. This is retained for compatibility with AxoSyslog version 1.6.x.

mark-freq()

Description: An alias for the obsolete mark() option, retained for compatibility with version 1.6.x.

The number of seconds between two MARK messages. MARK messages are generated when there was no message traffic to inform the receiver that the connection is still alive. If set to zero (0), no MARK messages are sent. The mark-freq() can be set for global option and/or every MARK capable destination driver if mark-mode() is periodical or dst-idle or host-idle. If mark-freq() is not defined in the destination, then the mark-freq() will be inherited from the global options. If the destination uses internal mark-mode(), then the global mark-freq() will be valid (does not matter what mark-freq() set in the destination side).

mark-mode()

Description: The mark-mode() option can be set for the following destination drivers: file(), program(), unix-dgram(), unix-stream(), network(), pipe(), syslog() and in global option.

• internal: When internal mark mode is selected, internal source should be placed in the log path as this mode does not generate mark by itself at the destination. This mode only yields the mark messages from internal source. This is the mode as AxoSyslog 3.3 worked. MARK will be generated by internal source if there was NO traffic on local sources:

  file(), pipe(), unix-stream(), unix-dgram(), program()

• dst-idle: Sends MARK signal if there was NO traffic on destination drivers. MARK signal from internal source will be dropped.

  MARK signal can be sent by the following destination drivers: network(), syslog(), program(), file(), pipe(), unix-stream(), unix-dgram().

• host-idle: Sends MARK signal if there was NO local message on destination drivers. for example, MARK is generated even if messages were received from tcp. MARK signal from internal source will be dropped.

  MARK signal can be sent by the following destination drivers: network(), syslog(), program(), file(), pipe(), unix-stream(), unix-dgram().

• periodical: Sends MARK signal perodically, regardless of traffic on destination driver. MARK signal from internal source will be dropped.

  MARK signal can be sent by the following destination drivers: network(), syslog(), program(), file(), pipe(), unix-stream(), unix-dgram().

• none: Destination driver drops all MARK messages. If an explicit mark-mode() is not given to the drivers where none is the default value, then none will be used.

• global: Destination driver uses the global mark-mode() setting. Note that setting the global mark-mode() to global causes a syntax error in AxoSyslog.

Available in AxoSyslog 3.4 and later.

normalize-hostnames()

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

on-error()

Description: Controls what happens when type-casting fails and AxoSyslog cannot convert some data to the specified type. By default, AxoSyslog drops the entire message and logs the error. Currently the value-pairs() option uses the settings of on-error().

• drop-message: Drop the entire message and log an error message to the internal() source. This is the default behavior of AxoSyslog.
• drop-property: Omit the affected property (macro, template, or message-field) from the log message and log an error message to the internal() source.
• fallback-to-string: Convert the property to string and log an error message to the internal() source.
• silently-drop-message: Drop the entire message silently, without logging the error.
• silently-drop-property: Omit the affected property (macro, template, or message-field) silently, without logging the error.
• silently-fallback-to-string: Convert the property to string silently, without logging the error.

owner()

Description: The default owner of output files. If set, syslog-ng changes the owner of accessed files (for example, /dev/null) to this value, and the permissions to the value set in the perm() option.

Starting with version 3.16, the default value of this option is -1, so AxoSyslog does not change the ownership, unless explicitly configured to do so.

pass-unix-credentials()

Description: Enable AxoSyslog to collect UNIX credential information (that is, the PID, user ID, and group of the sender process) for messages received using UNIX domain sockets. Available only in AxoSyslog 3.7 and later. Note that collecting UNIX credential information from sockets in high-traffic environments can be resource intensive, therefore pass-unix-credentials() can be disabled globally, or separately for each source.

perm()

Description: The default permission for output files. If set, syslog-ng changes the permissions of accessed files (for example, /dev/null) to this value, and the onwer to the value set in the owner() option.

Starting with version 3.16, the default value of this option is -1, so AxoSyslog does not change the permissions, unless explicitly configured to do so.

proto-template()

Description: Specifies a template that protocol-like destinations (for example, network() and syslog()) use by default. For example:

   template t_isostamp { template("$ISODATE $HOST $MSGHDR$MSG\n"); };
    
    options { proto-template(t_isostamp); };

recv-time-zone()

Description: Specifies the time zone associated with the incoming messages, if not specified otherwise in the message or in the source driver. For details, see also Timezones and daylight saving and A note on timezones and timestamps.

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.

send-time-zone()

Description: Specifies the time zone associated with the messages sent by syslog-ng, if not specified otherwise in the message or in the destination driver. For details, see Timezones and daylight saving.

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.

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.

stats()

Available in AxoSyslog 4.1 and later.

Description: The stats() option is a collection of statistics-related options.

options {
    stats(
        freq(1)
        level(1)
        lifetime(1000)
        max-dynamics(10000)
        syslog-stats(yes)
    );
};

freq()

Description: The period between two STATS messages in seconds. STATS are log messages sent by syslog-ng, containing statistics about dropped log messages. Set to 0 to disable the STATS messages.

level()

Description: Specifies the detail of statistics AxoSyslog collects about the processed messages.

• Level 0 collects only statistics about the sources and destinations.

• Level 1 contains details about the different connections and log files, but has a slight memory overhead.

• Level 2 contains detailed statistics based on the hostname.

• Level 3 contains detailed statistics based on various message parameters like facility, severity, or tags.

Note that level 2 and 3 increase the memory requirements and CPU load. For details on message statistics, see Statistics of AxoSyslog.

lifetime()

Description: Dynamic counters in metrics are pruned after lifetime expires. Note that orphaned counters are not pruned (you can prune them by running syslog-ng-ctl stats --remove-orphans).

max-dynamics()

Available in AxoSyslog 4.1 and later.

Description: To avoid performance issues or even overloading AxoSyslog (for example, if a script starts to send logs from different IP addresses to AxoSyslog), you might want to limit the number of registered dynamic counters in the message statistics. For details on message statistics, see Statistics of AxoSyslog.

• Unlimited dynamic counters:

  If you do not use this option, dynamic counters will not be limited. This can be useful in cases where you are extremely interested in dynamic counters, and use these statistics extensively.

  Warning In some cases, there might be even millions of dynamic counters

• Limited dynamic counter clusters:

  To limit dynamic counters, enter a number, and only a maximum of <number> counters will be registered in the statistics.

  In practice, this means dynamic counter clusters. A program name produces one dynamic counter cluster, that can include several counters, such as processed, stamp, and so on.

  Example: Limiting dynamic counter clusters 1:

  If you set stats-max-dynamics() to 1, and 2 programs send messages, only one of these programs will be tracked in the dynamic counters, but it will have more than one counters.

  Example: Limiting dynamic counter clusters 2:

  If you have 500 clients, and set stats-max-dynamics() to 1000, you will have enough number of counters reserved for these clients, but at the same time, you limit the use of your resources and therefore protect your system from being overloaded.

• No dynamic counters:

  To disable dynamic counters completely, set the value of this option to 0. This is the recommended value if you do not use statistics, or if you are not interested in dynamic counters in particular (for example, the number of logs arriving from programs).

syslog-stats()

Available in AxoSyslog 4.1 and later.

Description: Changes the behavior of counting messages based on different syslog fields, like SEVERITY, FACILITY, HOST.

Possible values:

• yes: Enable syslog stats.
• no: Disable syslog stats.
• auto: Use the setting of the old stats-level() option.

stats-freq()

Deprecated legacy option. Use stats(freq()) instead.

stats-level()

Deprecated legacy option. Use stats(level()) instead.

stats-max-dynamics()

Deprecated legacy option. Use stats(max-dynamics()) instead.

sync() or sync-freq() (DEPRECATED)

Description: Obsolete aliases for flush-lines()

threaded()

Description: Enable AxoSyslog to run in multithreaded mode and use multiple CPUs. Available only in AxoSyslog 3.3 and later. Note that setting threaded(no) does not mean that AxoSyslog will use only a single thread. For details, see Multithreading and scaling.

time-reap()

Description: The time to wait in seconds before an idle destination file or pipe is closed. Note that only destination files having macros in their filenames are closed automatically.

Starting with version 3.23, the way how time-reap() works is the following.

1. If the time-reap() option of the destination is set, that value is used, for example:

       destination d_fifo {
           pipe(
               "/tmp/test.fifo",
               time-reap(30)  # sets time-reap() for this destination only
           );
       };
   

2. If the time-reap() option of the destination is not set, and the destination does not use a template or macro in its filename or path, time-reap() is automatically set to 0. For example:

       destination d_fifo {
           pipe(
               "/tmp/test.fifo",
           );
       };
   

3. Otherwise, the value of the global time-reap() option is used, which defaults to 60 seconds.

time-reopen()

Description: The time to wait in seconds before a dead connection is reestablished.

time-sleep() (DEPRECATED)

Description: The time to wait in milliseconds between each invocation of the poll() iteration.

time-zone()

Description: Convert timestamps to the timezone specified by this option. If this option is not set, then the original timezone information in the message is used. Converting the timezone changes the values of all date-related macros derived from the timestamp, for example, HOUR. For the complete list of such macros, see Date-related macros.

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.

trim-large-messages()

Description: Determines what AxoSyslog does with incoming log messages that are received using the IETF-syslog protocol using the syslog() driver, and are longer than the value of log-msg-size(). Other drivers ignore the trim-large-messages() option.

• If set to no, AxoSyslog drops the incoming log message.

• If set to yes, AxoSyslog trims the incoming log message to the size set in log-msg-size(), and adds the trimmed tag to the message. The rest of the message is dropped. You can use the tag to filter on such messages.

      filter f_trimmed {
          tags("trimmed");
      };
  

  If AxoSyslog trims a log message, it sends a debug-level log message to its internal() source.

  As a result of trimming, a parser could fail to parse the trimmed message. For example, a trimmed JSON or XML message will not be valid JSON or XML.

Available in AxoSyslog version 3.21 and later.

ts-format()

Description: Specifies the timestamp format used when AxoSyslog itself formats a timestamp and nothing else specifies a format (for example: STAMP macros, internal messages, messages without original timestamps). For details, see also A note on timezones and timestamps.

By default, timestamps include only seconds. To include fractions of a second (for example, milliseconds) use the frac-digits() option.

use-dns()

Description: Enable or disable DNS usage. The persist_only option attempts to resolve hostnames locally from file (for example, from /etc/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.

use-fqdn()

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.

use-rcptid()

Description: When the use-rcptid global option is set to yes, AxoSyslog automatically assigns a unique reception ID to every received message. You can access this ID and use it in templates via the ${RCPTID} macro. The reception ID is a monotonously increasing 48-bit integer number, that can never be zero (if the counter overflows, it restarts with 1).

This option is deprecated, use the use-uniqid() option instead.

use-uniqid()

Description: This option enables generating a globally unique ID. It is generated from the HOSTID and the RCPTID in the format of HOSTID@RCPTID. It has a fixed length: 16+@+8 characters. You can include the unique ID in the message by using the macro. For details, see UNIQID.

Enabling this option automatically generates the HOSTID. The HOSTID is a persistent, 32-bits-long cryptographically secure pseudo random number, that belongs to the host that the AxoSyslog is running on. If the persist file is damaged, the HOSTID might change.

Enabling this option automatically enables the RCPTID functionality. For details, see RCPTID