rsyslog Properties — rsyslog 8.2412.0 documentation

# rsyslog Properties

Data items in rsyslog are called “properties”. They can have different origin. The most important ones are those that stem from received messages. But there are also others. Whenever you want to access data items, you need to access the respective property.

Properties are used in

- templates

- conditional statements

The property name is case-insensitive (prior to 3.17.0, they were case-sensitive).

Note: many users refer to “rsyslog properties” as “rsyslog variables”. You can treat them as synonymous. Read how rsyslog lead author Rainer Gerhards explains the naming difference.

## Message Properties

These are extracted by rsyslog parsers from the original message. All message properties start with a letter.

The following message properties exist:

msg

  the MSG part of the message (aka “the message” ;))

rawmsg

  the message “as is”. Should be useful for debugging and also if a message should be forwarded totally unaltered. Please notice EscapecontrolCharactersOnReceive is enabled by default, so it may be different from what was received in the socket.

rawmsg-after-pri

  Almost the same as rawmsg, but the syslog PRI is removed. If no PRI was present, rawmsg-after-pri is identical to rawmsg. Note that the syslog PRI is header field that contains information on syslog facility and severity. It is enclosed in greater-than and less-than characters, e.g. “<191>”. This field is often not written to log files, but usually needs to be present for the receiver to properly classify the message. There are some rare cases where one wants the raw message, but not the PRI. You can use this property to obtain that. In general, you should know that you need this format, otherwise stay away from the property.

hostname

  hostname from the message

source

  alias for HOSTNAME

fromhost

  hostname of the system the message was received from (in a relay chain, this is the system immediately in front of us and not necessarily the original sender). This is a DNS-resolved name, except if that is not possible or DNS resolution has been disabled.

fromhost-ip

  The same as fromhost, but always as an IP address. Local inputs (like imklog) use 127.0.0.1 in this property.

syslogtag

  TAG from the message

programname

  the “static” part of the tag, as defined by BSD syslogd. For example, when TAG is “named[12345]”, programname is “named”.

  Precisely, the programname is terminated by either (whichever occurs first):

  - end of tag

  - nonprintable character

  - ‘:’

  - ‘[’

  - ‘/’

  The above definition has been taken from the FreeBSD syslogd sources.

  Please note that some applications include slashes in the static part of the tag, e.g. “app/foo[1234]”. In this case, programname is “app”. If they store an absolute path name like in “/app/foo[1234]”, programname will become empty (“”). If you need to actually store slashes as part of the programname, you can use the global option

  global(parser.permitSlashInProgramName=”on”)

  to permit this. Then, a syslogtag of “/app/foo[1234]” will result in programname being “/app/foo”. Note: this option is available starting at rsyslogd version 8.25.0.

pri

  PRI part of the message - undecoded (single value)

pri-text

  the PRI part of the message in a textual form with the numerical PRI appended in brackets (e.g. “local0.err<133>”)

iut

  the monitorware InfoUnitType - used when talking to a MonitorWare backend (also for Adiscon LogAnalyzer)

syslogfacility

  the facility from the message - in numerical form

syslogfacility-text

  the facility from the message - in text form

syslogseverity

  severity from the message - in numerical form

syslogseverity-text

  severity from the message - in text form

syslogpriority

  an alias for syslogseverity - included for historical reasons (be careful: it still is the severity, not PRI!)

syslogpriority-text

  an alias for syslogseverity-text

timegenerated

  timestamp when the message was RECEIVED. Always in high resolution

timereported

  timestamp from the message. Resolution depends on what was provided in the message (in most cases, only seconds)

timestamp

  alias for timereported

protocol-version

  The contents of the PROTOCOL-VERSION field from IETF draft draft-ietf-syslog-protocol

structured-data

  The contents of the STRUCTURED-DATA field from IETF draft draft-ietf-syslog-protocol

app-name

  The contents of the APP-NAME field from IETF draft draft-ietf-syslog-protocol

procid

  The contents of the PROCID field from IETF draft draft-ietf-syslog-protocol

msgid

  The contents of the MSGID field from IETF draft draft-ietf-syslog-protocol

inputname

  The name of the input module that generated the message (e.g. “imuxsock”, “imudp”). Note that not all modules necessarily provide this property. If not provided, it is an empty string. Also note that the input module may provide any value of its liking. Most importantly, it is not necessarily the module input name. Internal sources can also provide inputnames. Currently, “rsyslogd” is defined as inputname for messages internally generated by rsyslogd, for example startup and shutdown and error messages. This property is considered useful when trying to filter messages based on where they originated - e.g. locally generated messages (“rsyslogd”, “imuxsock”, “imklog”) should go to a different place than messages generated somewhere else.

uuid

> Only Available if rsyslog is build with –enable-uuid

> A UUID for the message. It is not present by default, but will be created on first read of the uuid property. Thereafter, in the local rsyslog instance, it will always be the same value. This is also true if rsyslog is restarted and messages stayed in an on-disk queue.

> Note well: the UUID is not automatically transmitted to remote syslog servers when forwarding. If that is needed, a special template needs to be created that contains the uuid. Likewise, the receiver must parse that UUID from that template.

> The uuid property is most useful if you would like to track a single message across multiple local destination. An example is messages being written to a database as well as to local files.

jsonmesg

> Available since rsyslog 8.3.0

> The whole message object as JSON representation. Note that the JSON string will not include an LF and it will contain all other message properties specified here as respective JSON containers. It also includes all message variables in the “$!” subtree (this may be null if none are present).

> This property is primarily meant as an interface to other systems and tools that want access to the full property set (namely external plugins). Note that it contains the same data items potentially multiple times. For example, parts of the syslog tag will by contained in the rawmsg, syslogtag, and programname properties. As such, this property has some additional overhead. Thus, it is suggested to be used only when there is actual need for it.

## System Properties

These properties are provided by the rsyslog core engine. They are not related to the message. All system properties start with a dollar-sign.

Special care needs to be taken in regard to time-related system variables:

- `timereported` contains the timestamp that is contained within the message header. Ideally, it resembles the time when the message was created at the original sender. Depending on how long the message was in the relay chain, this can be quite old.

- `timegenerated` contains the timestamp when the message was received by the local system. Here “received” actually means the point in time when the message was handed over from the OS to rsyslog’s reception buffers, but before any actual processing takes place. This also means a message is “received” before it is placed into any queue. Note that depending on the input, some minimal processing like extraction of the actual message content from the receive buffer can happen. If multiple messages are received via the same receive buffer (a common scenario for example with TCP-based syslog), they bear the same `timegenerated` stamp because they actually were received at the same time.

- `$now` is not from the message. It is the system time when the message is being processed. There is always a small difference between `timegenerated` and `$now` because processing always happens after reception. If the message is sitting inside a queue on the local system, the time difference between the two can be some seconds (e.g. due to a message burst and in-memory queueing) up to several hours in extreme cases where a message is sitting inside a disk queue (e.g. due to a database outage). The `timereported` property is usually older than `timegenerated`, but may be totally different due to differences in time and time zone configuration between systems.

The following system properties exist:

$bom

  The UTF-8 encoded Unicode byte-order mask (BOM). This may be useful in templates for RFC5424 support, when the character set is know to be Unicode.

$myhostname

  The name of the current host as it knows itself (probably useful for filtering in a generic way)

### Time-Related System Properties

All of these system properties exist in a local time variant (e.g. $now) and a variant that emits UTC (e.g. $now-utc). The UTC variant is always available by appending “-utc”. Note that within a single template, only the localtime or UTC variant should be used. While it is possible to mix both variants within a single template, it is not guaranteed that they will provide exactly the same time. The technical reason is that rsyslog needs to re-query system time when the variant is changed. Because of this, we strongly recommend not mixing both variants in the same template.

Note that use in different templates will generate a consistent timestamp within each template. However, as $now always provides local system time at time of using it, time may advance and consequently different templates may have different time stamp. To avoid this, use timegenerated instead.

$now

  The current date stamp in the format YYYY-MM-DD

$year

  The current year (4-digit)

$month

  The current month (2-digit)

$day

  The current day of the month (2-digit)

$wday

  The current week day as defined by ‘gmtime()’. 0=Sunday, …, 6=Saturday

$hour

  The current hour in military (24 hour) time (2-digit)

$hhour

  The current half hour we are in. From minute 0 to 29, this is always 0 while from 30 to 59 it is always 1.

$qhour

  The current quarter hour we are in. Much like $HHOUR, but values range from 0 to 3 (for the four quarter hours that are in each hour)

$minute

  The current minute (2-digit)

$now-unixtimestamp

  The current time as a unix timestamp (seconds since epoch). This actually is a monotonically increasing counter and as such can also be used for any other use cases that require such counters. This is an example of how to use it for rate-limiting:

      # Get Unix timestamp of current message
      set $.tnow = $$now-unixtimestamp

      # Rate limit info to 5 every 60 seconds
      if ($!severity == 6 and $!facility == 17) then {
        if (($.tnow - $/trate) > 60) then {
          # 5 seconds window expired, allow more messages
          set $/trate = $.tnow;
          set $/ratecount = 0;
        }
        if ($/ratecount > 5) then {
          # discard message
          stop
        } else {
          set $/ratecount = $/ratecount + 1;
        }
      }

  NOTE: by definition, there is no “UTC equivalent” of the $now-unixtimestamp property.

See also

Help with configuring/using `Rsyslog`:

- Mailing list - best route for general questions

- GitHub: rsyslog source project - detailed questions, reporting issues that are believed to be bugs with `Rsyslog`

See also

Contributing to `Rsyslog`:

- Source project: rsyslog project README.

- Documentation: rsyslog-doc project README

Copyright 2008-2023 Rainer Gerhards (Großrinderfeld), and Others.