enter main process 2241
child process 2242 created by 2241
SIGCHLD from process 2242
normal termination, exit status = 1
waitpid returns -1
child process 2244 created by 2241
SIGCHLD from process 2244
normal termination, exit status = 0
waitpid returns 0
child process 2243 created by 2241
SIGCHLD from process 2243
abnormal termination, signal number = 6,
waitpid returns -1
main process 2241 exited