Filter log4j2 SYSTEM_ERR target logs on linux command line

Question

I am using log4j2 in my Java project and would like to filter for error logs on the linux console.

log4j2 is configured as followed:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration>
  <Properties>
    <Property name="pattern">[%d{yyyy-MM-dd HH:mm:ss.SSS}][%highlight{%-5level}][%t][%logger] %msg%n</Property>
  </Properties>
  <Appenders>
    <Console name="stdout" target="SYSTEM_OUT"> <!-- 1 -->
      <PatternLayout pattern="${pattern}"/>
      <ThresholdFilter level="ERROR" onMatch="DENY" onMismatch="ACCEPT"/> <!-- 3 -->
    </Console>
    <Console name="stderr" target="SYSTEM_ERR"> <!-- 2 -->
      <PatternLayout pattern="${pattern}"/>
      <ThresholdFilter level="ERROR" onMatch="ACCEPT" onMismatch="DENY"/> <!-- 3 -->
    </Console>
  </Appenders>
  <Loggers>
    <Root level="INFO">
      <AppenderRef ref="stdout"/> <!-- 4 -->
      <AppenderRef ref="stderr"/> <!-- 4 -->
    </Root>
  </Loggers>
</Configuration>

(found here: https://rmannibucau.metawerx.net/log4j2-error-log-event-on-stderr.html)

When I run my program via command line

java -jar program.jar 2>&1 >/dev/null

stdout is redirected to /dev/null while stderr is printed onscreen. (OK)

Strangely my LOGGER.error("...") trace is also redirected to /dev/null (which means it is logged on linux stdout) (NOK) while displayed in red (error) on my eclipse console (OK).

Am I missing something or why is my log4j2 stderr logger not logging to the linux stderr?

Redirects are read from right to left, so in your case stdout will be redirected to dev/null and stderr to stdout.To redirect only stderr to dev null use java -jar program.jar 2>/dev/null — LMC
I would like to redirect stdout to /dev/null and only print stderr But the program itself should print every log (info and higher) — Terel

Terel Terel · Accepted Answer · 2021-07-26T23:00:59

My logj42.xml was not included in the classpath. That's why the output of all log messages went to linux's stdout.

Filter log4j2 SYSTEM_ERR target logs on linux command line

1 Answers