---
title: "Log path flags"
url: "https://axoflow.com/docs/axosyslog-core/chapter-routing-filters/logpath/reference-logflags/"
last_modified: "2026-01-06T14:00:54+01:00"
---

> For the complete documentation index, see [llms.txt](https://axoflow.com/docs/axosyslog-core/llms.txt).

# Log path flags

Flags influence the behavior of `syslog-ng`, and the way it processes messages. The following flags may be used in the log paths, as described in [Log paths](https://axoflow.com/docs/axosyslog-core/chapter-routing-filters/logpath/index.md).

## Log statement flags

### catchall

This flag means that the source of the message is ignored, only the filters of the log path are taken into account when matching messages. A log statement using the `catchall` flag processes every message that arrives to any of the defined sources.

### drop-unmatched

This flag means that the message is dropped along a log path when it does not match a filter or is discarded by a parser. Without using the `drop-unmatched` flag, AxoSyslog would continue to process the message along alternative paths.

### fallback

This flag makes a log statement ‘fallback’. Fallback log statements process messages that were not processed by other, ’non-fallback’ log statements.

Processed means that every filter of a log path matched the message. Note that in the case of embedded log paths, the message is considered to be processed if it matches the filters of the outer log path, even if it does not match the filters of the embedded log path. For details, see [Example: Using log path flags](https://axoflow.com/docs/axosyslog-core/chapter-routing-filters/logpath/reference-logflags/index.md).

### final

This flag means that the processing of log messages processed by the log statement ends here, other log statements appearing later in the configuration file will not process the messages processed by the log statement labeled as ‘final’. Note that this does not necessarily mean that matching messages will be stored only once, as there can be matching log statements processed before the current one (AxoSyslog evaluates log statements in the order they appear in the configuration file).

Processed means that every filter of a log path matched the message. Note that in the case of embedded log paths, the message is considered to be processed if it matches the filters of the outer log path, even if it does not match the filters of the embedded log path. For details, see [Example: Using log path flags](https://axoflow.com/docs/axosyslog-core/chapter-routing-filters/logpath/reference-logflags/index.md).

### flow-control

Enables flow-control to the log path, meaning that AxoSyslog will stop reading messages from the sources of this log statement if the destinations are not able to process the messages at the required speed. If disabled, AxoSyslog will drop messages if the destination queues are full. If enabled, AxoSyslog will only drop messages if the destination queues/window sizes are improperly sized. 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). Starting with version 4.12, you can enable flow-control for every log path using the [`log-flow-control()` global option](https://axoflow.com/docs/axosyslog-core/chapter-global-options/reference-options/index.md#global-option-log-flow-control).

### no-flow-control

Available in AxoSyslog 4.12 and later.

Disables flow-control for a log path if the [`log-flow-control()` global option](https://axoflow.com/docs/axosyslog-core/chapter-global-options/reference-options/index.md#global-option-log-flow-control) is enabled.

Using the `flow-control` and `no-flow-control` flags, you can enable/disable flow-control just the way you want. This can be especially useful for multi-level [Embedded log statements](https://axoflow.com/docs/axosyslog-core/chapter-routing-filters/logpath/concepts-embedded-logpaths/index.md).

> **Warning:**
> The `final`, `fallback`, and `catchall` flags apply only for the top-level log paths, they have no effect on embedded log paths.

## Example: Using log path flags

Let’s suppose that you have two hosts (`myhost_A` and `myhost_B`) that run two applications each (`application_A` and `application_B`), and you collect the log messages to a central AxoSyslog server. On the server, you create two log paths:

- one that processes only the messages sent by `myhost_A`, and
- one that processes only the messages sent by `application_A`.

This means that messages sent by `application_A` running on `myhost_A` will be processed by both log paths, and the messages of `application_B` running on `myhost_B` will not be processed at all.

- If you add the `final` flag to the first log path, then only this log path will process the messages of `myhost_A`, so the second log path will receive only the messages of `application_A` running on `myhost_B`.
- If you create a third log path that includes the `fallback` flag, it will process the messages not processed by the first two log paths, in this case, the messages of `application_B` running on `myhost_B`.
- Adding a fourth log path with the `catchall` flag would process every message received by the AxoSyslog server.

  ```shell
  log { source(s_localhost); destination(d_file); flags(catchall); };
  ```

The following example shows a scenario that can result in message loss. Do NOT use such a configuration, unless you know exactly what you are doing. The problem is if a message matches the filters in the first part of the first log path, AxoSyslog treats the message as ‘processed’. Since the first log path includes the `final` flag, AxoSyslog will not pass the message to the second log path (the one with the `fallback` flag). As a result, AxoSyslog drops messages that do not match the filter of the embedded log path.

```shell
# Do not use such a configuration, unless you know exactly what you are doing.
log {
    source(s_network);
    # Filters in the external log path.
    # If a message matches this filter, it is treated as 'processed'
    filter(f_program);
    filter(f_message);
    log {
        # Filter in the embedded log path.
        # If a message does not match this filter, it is lost, it will not be processed by the 'fallback' log path
        filter(f_host);
        destination(d_file1);
    };
    flags(final);
};

log {
    source(s_network);
    destination(d_file2);
    flags(fallback);
};
```

## Example: Using the drop-unmatched flag

In the following example, if a log message arrives whose `$MSG` part does not contain the string `foo`, then AxoSyslog will discard the message and will not check compliance with the second `if` condition.

```shell
...
if {
    filter { message('foo') };
    flags(drop-unmatched)
};
if {
    filter { message('bar') };
};
...
```

(Without the `drop-unmatched` flag, AxoSyslog would check if the message complies with the second `if` condition, that is, whether or not the message contains the string `bar` .)

Last modified January 6, 2026: [Markdown formatting cleanups (75624024)](https://github.com/axoflow/axosyslog-core-docs/commit/756240240accdc58edd232b7f2aae890593200a6)