Are kernel threads really kernel processes?

Question

I've read in many places that Linux creates a kernel thread for each user thread in a Java VM. (I see the term "kernel thread" used in two different ways:

1. a thread created to do core OS work and
2. a thread the OS is aware of and schedules to perform user work.

I am talking about the latter type.)

Is a kernel thread the same as a kernel process, since Linux processes support shared memory spaces between parent and child, or is it truly a different entity?

Answer 1

There is absolutely no difference between a thread and a process on Linux. If you look at clone(2) you will see a set of flags that determine what is shared, and what is not shared, between the threads.

Classic processes are just threads that share nothing; you can share what components you want under Linux.

This is not the case on other OS implementations, where there are much more substantial differences.

Answer 2

Threads are processes under Linux. They are created with the clone system call, which returns a process ID that can be sent a signal via the kill system call, just like a process. Thread processes are visible in ps output. The clone call is passed flags which determine how much of the parent process's environment is shared with the thread process.