[dx@bolsa test/asd/arise]$ cat asd.c
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>

int main() {
    int fd = open("/tmp/lol", O_RDONLY);
    printf("fd == %d\n", fd);
    system("ls -l /proc/self/{exe,fd}");
    close(fd);
    return 0;
}
[dx@bolsa test/asd/arise]$ gcc asd.c -o asd && ./asd
fd == 3
lrwxrwxrwx 1 dx users 0 Apr  3 12:51 /proc/self/exe -> /usr/bin/ls

/proc/self/fd:
total 0
lrwx------ 1 dx users 64 Apr  3 12:51 0 -> /dev/pts/8
lrwx------ 1 dx users 64 Apr  3 12:51 1 -> /dev/pts/8
lrwx------ 1 dx users 64 Apr  3 12:51 2 -> /dev/pts/8
lr-x------ 1 dx users 64 Apr  3 12:51 3 -> /tmp/lol
lr-x------ 1 dx users 64 Apr  3 12:51 4 -> /proc/4324/fd