Hi, All Thanks very much, I get it. The tid returned by pthread_self() is posix thread id. The tid returned by gettid() is linux thread id which is the pid of the lightweight process. The pid returned by getpid() is linux thread goup id which is the tgid of the lightweight process. That's right? Regard, Cheng -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/