Why do some JVM/Linux Kernels show each java thread as a process and other not? How can I determine beforehand what the behavior will be?

Question

I have two machines, one running 2.4.18 and one running 2.4.20. Both run Java 1.5 build 13. On one machine (2.4.18), each thread shows up as a separate process in the ps output, and on the other the whole JVM shows up as one process. What is the distinguishing factor and can I control it?

Answer 1

I know thread models changed sometime around that period (e.g. 1:1 on user:kernel mappings) I don't recall however if it actually was 2.4.19+ that did it? (Don't mean to answer with another question)

Answer 2

I believe this was to do with how the Linux kernel and/or the ps command handled multi-threaded processes. Earlier versions displayed each thread as a separate entry, newer versions merged them into one.

I was under the impression that this changed with kernel 2.6, but it seems it changed earlier than that.

I don't think there's anything you can do to fix this, short of upgrading the kernel. Perhaps an upgrade to ps might fix it, if that's actually where the problem was.