Why doesn’t Linux prevent spawning infinite number of processes and crashing?

With the very simple code below, my system (Ubuntu Linux 14.04) simply crashes not even letting my mouse respond. I had to force quit with the power button. I thought Linux is a stable OS tolerable of handling such basic program errors. Did I miss something?

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <semaphore.h>

void check(int isOkay){
  if(!isOkay){
    printf("errorn");
    abort();
  }
}

int main(void){
  #define n 1000000
  int array[n];
  sem_t blocker;
  int i;

  while(1){
    if(!fork()){
      for(i = 0; i < n; ++i){
        array[i] = rand();
      }
      check(sem_init(&blocker, 0, 0) == 0);
      check(sem_wait(&blocker) == 0);
    }
  }
  return 0;
}

Answer

Congratulations, you’ve discovered the fork bomb. There are shell one-liners that can wreak the same sort of havic with a lot less typing on your part.

It is in fact possible to limit the number of processes that a user can spawn using ulimit — see the bottom of the linked wikipedia articles for details.

A desktop install of Ubuntu is not exactly a hardened server, though. It’s designed for usability first and foremost. If you need a locked down system that can’t crash, there are better options.