log4j2: Include PID

Question

I'm using log4j2, and running multiple instances of the same code in different processes (ie different JVMs) at the same time. I'd like all processes to log to the same file, interleaved How can I configure (via log4j2.xml) to output the PID, so that the different processes can be distinguished in the logs?

Dagny

I would be surprised if you can log from multiple JVMs to the same file. Happy to be proven wrong. Chronicle Logger does this, but it's not trivial to implement. – Little

@PeterLawrey - Doing it right now, works fine out of the box. The log lines are interleaved in the file. – Dagny

Are you asking how your Java program can get its PID, so it can include it in log mrssages you generate. Or are you asking how to configure log4j so it inserts the PID in log messages? – Openwork

I agree with Peter. This may (seem to) work but may turn out to be fragile if you do things like rollover. Log4j2 (as of v2.0.2) is not designed for this usage. – Bloodfin

@Openwork - Yes, how to configure log4j so that it inserts the PID, or some other way of identifying the process, in the log message – Dagny

@RemkoPopma It's okay if the log doesn't handle rollover – Dagny

Rather than plaving clarifications in comments, edit your question so it is clearer. – Openwork

Interesting to hear this works. Are you using FileAppender or RandomAccessFileAppender? – Bloodfin

Answer 1

There is a plugin ProcessIdPatternConverter in log4j2-core since version 2.9 that does exactly this.

just setting %pid or %processId in the pattern layout logs it.

log4j documentation: https://logging.apache.org/log4j/2.x/manual/layouts.html

Barye

Adding %pid is printing the level info since the meta character for level info is "%p" so if i use %pid it prints "ERRORid" rather than printing the process id. Any alternatives for this? – Schoenfelder

Did you add log4j2-core library to your dependencies? – Mcalister

Works as expected. Tested with version 2.14.1 and %processId dumps the process id of the process. – Oddfellow

Answer 2

Perhaps MDC can help you. Try this:

Java:

import java.lang.management.ManagementFactory;

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.apache.logging.log4j.ThreadContext;

public class TestPID {

    private static final Logger LOG = LogManager.getLogger(TestPID.class);

    static {
        // Get the process id
        String pid = ManagementFactory.getRuntimeMXBean().getName().replaceAll("@.*", "");

        // MDC
        ThreadContext.put("pid", pid);
    }

    public static void main(String[] args) {
        LOG.info("Testing...");
    }

}

XML:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration>
  <Appenders>
    <Console name="Console" target="SYSTEM_OUT">
      <PatternLayout pattern="%d %5X{pid} %-5p %c#%M - %m%n" />
    </Console>
  </Appenders>
  <Loggers>
    <Root level="info">
      <AppenderRef ref="Console" />
    </Root>
  </Loggers>
</Configuration>

Output:

2014-09-10 00:13:49,281  7164 INFO  TestPID#main - Testing...
                         ↑↑↑↑
                    That's the PID

---

You may want to see:

• Layouts - PatternLayout
• Effective Logging in Java/JEE – Mapped Diagnostic Context
• How can a Java program get its own process ID?
• How to use MDC with thread pools?

Nightcap

Answer 3

If you are using spring framework, you just need to append " ${PID}" inside pattern value, that's it. No need to add a new function to fetch your processId as mentioned in other answers.

Shearwater

It would be helpful if you provided detailed example of configuration with ${PID} variable. – Wolsky

Answer 4

log4j.appender.consoleAppender.layout.ConversionPattern=%-25d %-5p ${PID} [%-10t] %c{3} - %m%n

resulted in

2021-03-23 11:42:57.281  INFO 896 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/v1]     : Initializing Spring FrameworkServlet 'dispatcherServlet'
2021-03-23 11:43:02,766   INFO  896 [http-nio-8080-exec-4] springboot.controller.MyController - greeting(/v1)

Roby