How can I view threads for a running process that is creating threads?

I made a very small program that creates two threads: #include #include #include void *start() { printf("Am a new thread!\n"); printf("%d\n",pthread_self()); } void main() { pthread_t thread_id1; pthread_t thread_id2; pthread_create(&thread_id1,NULL,start,NULL); pthread_create(&thread_id2,NULL,start,NULL); //pthread_join(thread_id,NULL); sleep(30); } When I compile and run the program with: gcc create.c -lpthread ./a.out And I open a new terminal and try to view the threads, this is what I get: ps -efL | grep a.out root 1943 20158 1943 0 1 15:25 pts/4 00:00:00 ./a.out root 1985 1889 1985 0 1 15:25 pts/5 00:00:00 grep --color=auto a.out So why can't I see two thread ids here?