perl -MBSD::Resource -le'setrlimit(RLIMIT_NPROC,20,10);
  system qq(echo 1);' # succeeds
perl -MBSD::Resource -le'setrlimit(RLIMIT_NPROC,2,1);
  system qq(echo 1);' # succeeds
perl -MBSD::Resource -le'setrlimit(RLIMIT_NPROC,2,1);
  for(1..10){if(fork==0){print"child $_";sleep 1;exit}};
  waitpid(-1,0)' # succeeds, prints "child 1".."child 10"