Compatibility Notes for rsyslog v7 — rsyslog 8.24.0 documentation

# Compatibility Notes for rsyslog v7

This document describes things to keep in mind when moving from v6 to v7. It does not list enhancements nor does it talk about compatibility concerns introduced by earlier versions (for this, see their respective compatibility documents). Its focus is primarily on what you need to know if you used v6 and want to use v7 without hassle.

Version 7 builds on the new config language introduced in v6 and extends it. Other than v6, it not just only extends the config language, but provides considerable changes to core elements as well. The result is much more power and ease of use as well (this time that is not contradictionary).

## BSD-Style blocks

BSD style blocks are no longer supported (for good reason). See the rsyslog BSD blocks info page for more information and how to upgrade your config.

## CEE-Properties

In rsyslog v6, CEE properties could not be used across disk-based queues. If this was done, their content was reset. This was a missing feature in v6. In v7, this feature has been implemented. Consequently, situations where the previous behaviour were desired need now to be solved differently. We do not think that this will cause any problems to anyone, especially as in v6 this was announced as a missing feature.

## omusrmsg: using just a username or “*” is deprecated

In legacy config format, the asterisk denotes writing the message to all users. This is usually used for emergency messages and configured like this:

    *.emerg  *

Unfortunately, the use of this single character conflicts with other uses, for example with the multiplication operator. While rsyslog up to versions v7.4 preserves the meaning of asterisk as an action, it is deprecated and will probably be removed in future versions. Consequently, a warning message is emitted. To make this warning go away, the action must be explicitly given, as follows:

    *.emerg  :omusrmsg:*

The same holds true for user names. For example

    *.emerg  john

at a minimum should be rewritten as

    *.emerg  :omusrmsg:john

Of course, for even more clarity the new RainerScript style of action can also be used:

    *.emerg  action(type="omusrmsg" users="john")

In Rainer’s blog, there is more background information on why omusrmsg needed to be changed available.

## omruleset and discard (~) action are deprecated

Both continue to work, but have been replaced by better alternatives.

The discard action (tilde character) has been replaced by the “stop” RainerScript directive. It is considered more intuitive and offers slightly better performance.

The omruleset module has been replaced by the “call” RainerScript directive. Call permits to execute a ruleset like a subroutine, and does so with much higher performance than omruleset did. Note that omruleset could be run off an async queue. This was more a side than a desired effect and is not supported by the call statement. If that effect was needed, it can simply be simulated by running the called rulesets actions asynchronously (what in any case is the right way to handle this).

Note that the deprecated modules emit warning messages when being used. They tell that the construct is deprecated and which statement is to be used as replacement. This does not affect operations: both modules are still fully operational and will not be removed in the v7 timeframe.

## Retries of output plugins that do not do proper replies

Some output plugins may not be able to detect if their target is capable of accepting data again after an error (technically, they always return OK when TryResume is called). Previously, the rsyslog core engine suspended such an action after 1000 successive failures. This lead to potentially a large amount of errors and error messages. Starting with 7.2.1, this has been reduced to 10 successive failures. This still gives the plugin a chance to recover. In extreme cases, a plugin may now enter suspend mode where it previously did not do so. In practice, we do NOT expect that.

## omfile: file creation time

Originally, omfile created files immediately during startup, no matter if they were written to or not. In v7, this has changed. Files are only created when they are needed for the first time.

Also, in pre-v7 files were created before privileges were dropped. This meant that files could be written to locations where the actual desired rsyslog user was not permitted to. In v7, this has been fixed. This is fix also the prime reason that files are now created on demand (which is later in the process and after the privilege drop).

## Notes for the 7.3/7.4 branch

### “last message repeated n times” Processing

This processing has been optimized and moved to the input side. This results in usually far better performance and also de-couples different sources from the same processing. It is now also integrated in to the more generic rate-limiting processing.

#### User-Noticable Changes

The code works almost as before, with two exceptions:

- The suppression amount can be different, as the new algorithm precisely check’s a single source, and while that source is being read. The previous algorithm worked on a set of mixed messages from multiple sources.
- The previous algorithm wrote a “last message repeated n times” message at least every 60 seconds. For performance reasons, we do no longer do this but write this message only when a new message arrives or rsyslog is shut down.

Note that the new algorithms needs support from input modules. If old modules which do not have the necessary support are used, duplicate messages will most probably not be detected. Upgrading the module code is simple, and all rsyslog-provided plugins support the new method, so this should not be a real problem (crafting a solution would result in rather complex code - for a case that most probably would never happen).

#### Performance Implications

In general, the new method enables far faster output processing. However, it needs to be noted that the “last message repeated n” processing needs parsed messages in order to detect duplicated. Consequently, if it is enabled the parser step cannot be deferred to the main queue processing thread and thus must be done during input processing. The changes workload distribution and may have (good or bad) effect on the overall performance. If you have a very high performance installation, it is suggested to check the performance profile before deploying the new version.

Note: for high-performance environments it is highly recommended NOT to use “last message repeated n times” processing but rather the other (more efficient) rate-limiting methods. These also do NOT require the parsing step to be done during input processing.

### Stricter string-template Processing

Previously, no error message for invalid string template parameters was generated. Rather a malformed template was generated, and error information emitted at runtime. However, this could be quite confusing. Note that the new code changes user experience: formerly, rsyslog and the affected actions properly started up, but the actions did not produce proper data. Now, there are startup error messages and the actions are NOT executed (due to missing template due to template error).