Maybe this can still be worked around by copying the target fd first so it can be closed after fdup()ing the source fd, e.g. // Assume x and y are open fds and

Maybe this can still be worked around by copying the target fd first so it can be closed after fdup()ing the source fd, e.g. // Assume x and y are open fds and we want to replace y with a copy of x z = open("/dev/null", O_RDONLY); // Guarantees no other thread is using z dup2(y, z); dup2(x, y); close(z);