Maximum number of child process in Unix

Question

I have a question going in my mind. I just want to know what is the maximum limit on the number of child process when it is created by a process by using fork() system call? I am using UBUNTU OS (12.04) with kernel 3.2.0-45-generic.

Answer 1

Programmatically,

#include <stdio.h>
#include <sys/resource.h>

int main()
{
    struct rlimit rl;
    getrlimit(RLIMIT_NPROC, &rl);
    printf("%d\n", rl.rlim_cur);
}

where struct rlimit is:

struct rlimit {
    rlim_t rlim_cur;  /* Soft limit */
    rlim_t rlim_max;  /* Hard limit (ceiling for rlim_cur) */
};

From man:

RLIMIT_NPROC

The maximum number of processes (or, more precisely on Linux, threads) that can be created for the real user ID of the calling process. Upon encountering this limit, fork(2) fails with the error EAGAIN.