the return value of getpid() called from main thread and new thread r identical !!!

in linux, the clone system call is used to implement thread.

every thread is a light-weight process .

So, value returned from getpid() from main thread is expected to be different from value returned from getpid() from main thread. But the following code on my system( kernel 2.6.18 ) shows that.

void* f(void* arg) { printf("thread: PID: %d, thread ID %u\n", getpid(), pthread_self()); } int main(int argc, char** argv) { int err; pthread_t tid; err = pthread_create(&tid, NULL, f, NULL); if (err!=0) fprintf(stderr, "failed!\n"); printf("main: PID: %d, thread ID %u\n", getpid(), pthread_self()); pause(); exit(0); } $./a.out main: PID: 3666, thread ID 3085272768 thread: PID: 3666, thread ID 3085269936

But. APUE said these 2 process IDs will not match ...
Has 2.6.x changed the way it implement thread ?

You may be thinking of fork. Threads are still a part of the same process.
ta0kira

APUE was written a little while ago (although still a great book).
FYI, I wrote a multi-thr prog (in Perl) a while ago on a 2.4 kernel, and (if you ran top cmd) each thr had it's own unique pid (as you expected above).
However, when it was ported to a 2.6 kernel, you only see 1 pid (that of the 'parent' thr) once.

Tku for your reply to have my supposition confirmed.