# sysctl kernel.pid_max  kernel.pid_max = 32768  # sysctl -w kernel.pid_max=500  kernel.pid_max = 500  

#include <unistd.h>  #include <stdio.h>   int main ()   {       pid_t fpid; //fpid表示fork函数返回的值      int count=0;    while(1) {         fpid=fork();           if (fpid < 0) {               printf("error in fork!\n");            break;        }        else if (fpid == 0) {            count++;        } else {        sleep(100);        return 0;        }    }    printf("count is %d\n", count);    return 0;}

# gcc test.c; ./a.out   error in fork!  count is 172