IBM J9 or Eclipse open J9 error file. - unix1998/technical_notes GitHub Wiki

IBM J9 JVM, now known as Eclipse OpenJ9, also generates error logs when the JVM encounters a fatal error, similar to the hs_err_pid<pid>.log files produced by the HotSpot JVM. The naming and format might differ, but the purpose remains the same: to provide detailed diagnostic information useful for debugging JVM crashes.

In OpenJ9, these logs are typically called "javacore" files and "heapdumps." Here's a brief overview:

1. Javacore Files: These files provide a snapshot of the JVM at the time of the error. They contain information such as the state of all threads, stack traces, garbage collection history, and system properties. The default naming convention for these files is javacore.<timestamp>.<pid>.txt.

2. Heapdumps: These files provide a snapshot of the Java heap memory at the time of the crash. They are useful for analyzing memory usage and diagnosing memory leaks. The default naming convention for these files is heapdump.<timestamp>.<pid>.phd.

Similar to HotSpot, OpenJ9 allows customization of the error log generation through JVM options. For instance:

• To specify the directory for javacore files, you can use:

  -Xdump:java:file=/path/to/logs/javacore.%Y%m%d.%H%M%S.%pid.txt

• To specify the directory for heapdump files, you can use:

  -Xdump:heap:file=/path/to/logs/heapdump.%Y%m%d.%H%M%S.%pid.phd

If an OpenJ9 JVM encounters a fatal error, it might generate a file like this:

• javacore.20240605.123456.1234.txt where 20240605 is the date, 123456 is the time, and 1234 is the process ID.
• heapdump.20240605.123456.1234.phd with a similar naming convention.

Both HotSpot and OpenJ9 JVMs generate detailed error logs when they encounter fatal errors. While HotSpot uses the hs_err_pid<pid>.log format, OpenJ9 generates javacore and heapdump files with different naming conventions but similar purposes. These logs are crucial for diagnosing and resolving JVM issues.