$ cat a.c

#define _LARGEFILE_SOURCE

#define _LARGEFILE64_SOURCE

#define _FILE_OFFSET_BITS 64



#include <sys/types.h>

#include <sys/stat.h>

#include <unistd.h>

#include <stdio.h>

#include <fcntl.h>



int main()

{

    printf("sizeof(off_t) = %d
", sizeof(off_t));

    int fd = open("test", O_WRONLY | O_CREAT | O_LARGEFILE, 0600);

    if ( fd > 0 )

    {

        off_t l = 2047LL * 1024 * 1024 * 1024;

        off_t l_new = lseek(fd, l, SEEK_SET);

        write(fd, &fd, sizeof(fd));

        close(fd);

    }

}



$ gcc a.c -o a -std=c99

$ ./a

sizeof(off_t) = 8

$ ls -l test

-rw-------    1 root root  2197949513732 Jan 17 14:26 test