SCMP_ACT_NOTIFY
              A monitoring process will be notified when a process running  the
              seccomp filter calls a syscall that matches the filter rule.  The
              process  that  invokes  the syscall waits in the kernel until the
              monitoring process has responded via seccomp_notify_respond (3) .

              When a filter utilizing SCMP_ACT_NOTIFY is loaded into  the  ker‐
              nel,  the kernel generates a notification fd that must be used to
              communicate between the monitoring process  and  the  process(es)
              being filtered.  See seccomp_notif_fd (3) for more information.