err := retryWithBuffer(userBuffer, func(buf []byte) syscall.Errno {
		var errno syscall.Errno
		pwd, found, errno = _C_getpwnam_r((*_C_char)(unsafe.Pointer(&nameC[0])),
			(*_C_char)(unsafe.Pointer(&buf[0])), _C_size_t(len(buf)))
		return errno
	})
	if err == syscall.ENOENT || (err == nil && !found) {
		return nil, UnknownUserError(username)
	}
	if err != nil {
		return nil, fmt.Errorf("user: lookup username %s: %v", username, err)