reslimit.c

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

typedef struct rlimit rlimit_t;

int main(void)
{
    rlimit_t *r = (rlimit_t *) malloc(sizeof(struct rlimit));
    getrlimit(RLIMIT_NOFILE, r);
    printf("FILE: cur %d, max %d\n", (int) r->rlim_cur, (int) r->rlim_max);

    rlimit_t *new_r = (rlimit_t *) malloc(sizeof(struct rlimit));
    new_r->rlim_cur = (rlim_t) 2048;
    new_r->rlim_max = (rlim_t) 2048;
    if (setrlimit(RLIMIT_NOFILE, new_r)) {
        perror("setrlimit failed");
    }

    getrlimit(RLIMIT_NOFILE, r);
    printf("FILE: cur %d, max %d\n", (int) r->rlim_cur, (int) r->rlim_max);

    free(new_r);
    free(r);
    return 0;
}

maoe@maoe ~/coding/c/reslimit
$ gcc -Wall -std=c99 reslimit.c 
maoe@maoe ~/coding/c/reslimit
$ ./a.out 
FILE: cur 1024, max 1024
setrlimit falied: Operation not permitted
FILE: cur 1024, max 1024
maoe@maoe ~/coding/c/reslimit
$ sudo ./a.out 
FILE: cur 1024, max 1024
FILE: cur 2048, max 2048