tokuhirom released Linux::Socket::Accept4 that provides accept4(2) Monoceros-0.25 uses accept4 if Linux::Socket::Accept4 is avaliable. accept4(2) can set FD_CLOEXEC and O_NONBLOCK in one system call. Monoceros-0.24 select(16, [4 10], NULL, NULL, {1, 0}) = 1 (in [4], left {0, 999997}) accept(4, {sa_family=AF_INET, sin_port=htons(41296), sin_addr=inet_addr("127.0.0.1")}, [16]) = 6 ioctl(6, SNDCTL_TM