Increase the number of open files for a running process (without using GDB)

prlimit.c

#define _GNU_SOURCE  
#define _FILE_OFFSET_BITS 64  
#include <stdio.h>  
#include <time.h>  
#include <stdlib.h>  
#include <unistd.h>  
#include <sys/resource.h>  
  
#define errExit(msg)     do { perror(msg); exit(EXIT_FAILURE); \  
                        } while (0)  
  
int  
main(int argc, char *argv[])  
{  
    struct rlimit old, new;  
    struct rlimit *newp;  
    pid_t pid;  
  
    if (!(argc == 2 || argc == 4)) {  
        fprintf(stderr, "Usage: %s <pid> [<new-soft-limit> "  
                "<new-hard-limit>]\n", argv[0]);  
        exit(EXIT_FAILURE);  
    }  
  
    pid = atoi(argv[1]);        /* PID of target process */  
  
    newp = NULL;  
    if (argc == 4) {  
        new.rlim_cur = atoi(argv[2]);  
        new.rlim_max = atoi(argv[3]);  
        newp = &new;  
    }  
  
    /* Set the open files of target process; retrieve and display  
       previous limit */  
  
    if (prlimit(pid, RLIMIT_NOFILE, newp, &old) == -1)  
        errExit("prlimit-1");  
    printf("Previous limits: soft=%lld; hard=%lld\n",  
            (long long) old.rlim_cur, (long long) old.rlim_max);  
  
    /* Retrieve and display new open files limit */  
  
    if (prlimit(pid, RLIMIT_NOFILE, NULL, &old) == -1)  
        errExit("prlimit-2");  
    printf("New limits: soft=%lld; hard=%lld\n",  
            (long long) old.rlim_cur, (long long) old.rlim_max);  
  
    exit(EXIT_FAILURE);  
}

I had to collapse this line:
https://gist.github.com/alq666/c22e13df91d437ef0dcc#file-prlimit-c-L9