Log messages appear to be trimmed when using PatternLayout %m%n

[veenaBOL]

Description

We are observing that log messages are getting truncated when logged using Log4j, particularly when using the following configuration:

This impacts critical logs such as log.fatal(message, throwable) where the complete message or stack trace is not fully printed. This is particularly noticeable for fatal and error logs where the message size is significantly large.

Configuration

Version: 2.25.3

Operating system: macOS 15.6

JDK: OpenJDK 17.0.12

Reproduction

1. Configure Log4j with:

2. Log a message with a large string or exception:

3. log.fatal("Large message...", throwable);
   Check the output logs.

[vy]

@veenaBOL, would you mind providing a minimal reproducer (composed of a pom.xml and a src/main/java/Repro.java), please?

If you're using log4j-to-slf4j, you might be bitten by #4068. If so, would you mind verifying if #4089 fixes your problem, please?