FAT_IOCTL_GET_VOLUME_ID(2const)

💖 FAT_IOCTL_GET_VOLUME_ID(2const) 💖

okay so bestie, welcome to this 2const manual page, literally the cutest lil corner of the Linux man-pages ✨ (a 2const page is like a lil sidekick page for a specific constant, not a whole syscall, iykyk)

---

🌸 NAME 🌸

FAT_IOCTL_GET_VOLUME_ID — read the volume ID in a FAT filesystem

🎀 LIBRARY 🎀

Standard C library (libc, -lc)

✨ SYNOPSIS ✨

#include <linux/msdos_fs.h>  /* Definition of FAT_* constants */
#include <sys/ioctl.h>

int ioctl(int fd, FAT_IOCTL_GET_VOLUME_ID, uint32_t *id);

---

💅 DESCRIPTION 💅

so FAT filesystems are identified by a volume ID. iconic. and you can read that volume ID with FAT_IOCTL_GET_VOLUME_ID. that's literally the whole job, no cap 🫶

the fd argument can be a file descriptor for any file or directory of the filesystem. you don't need anything fancy — it's sufficient to create the file descriptor by calling open(2) with the O_RDONLY flag. lowkey the easiest setup ever.

the id argument is a pointer to the field that will get filled with the volume ID. typically the volume ID is displayed to the user as a group of two 16-bit fields:

printf("Volume ID %04x-%04x\n", id >> 16, id & 0xFFFF);

so cute, so tidy, two lil 16-bit halves holding hands 💞

---

🔥 RETURN VALUE 🔥

• on success, 0 is returned — slay ✨
• on error, -1 is returned, and errno is set to indicate the error 💀

---

👑 STANDARDS 👑

Linux. (periodt.)

🦋 HISTORY 🦋

Linux 3.11.

---

🌈 EXAMPLES 🌈

the following program demonstrates the use of ioctl(2) to display the volume ID of a FAT filesystem. main character energy fr fr.

the following output was recorded when applying the program for directory /mnt/user:

$ ./display_fat_volume_id /mnt/user
Volume ID 6443-6241

🍓 Program source (display_fat_volume_id.c) 🍓

#include <fcntl.h>
#include <linux/msdos_fs.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <unistd.h>

int
main(int argc, char *argv[])
{
    int       fd;
    int       ret;
    uint32_t  id;

    if (argc != 2) {
        printf("Usage: %s FILENAME\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    fd = open(argv[1], O_RDONLY);
    if (fd == -1) {
        perror("open");
        exit(EXIT_FAILURE);
    }

    /*
     * Read volume ID.
     */
    ret = ioctl(fd, FAT_IOCTL_GET_VOLUME_ID, &id);
    if (ret == -1) {
        perror("ioctl");
        exit(EXIT_FAILURE);
    }

    /*
     * Format the output as two groups of 16 bits each.
     */
    printf("Volume ID %04x-%04x\n", id >> 16, id & 0xFFFF);

    close(fd);

    exit(EXIT_SUCCESS);
}

---

💜 SEE ALSO 💜

ioctl(2), ioctl_fat(2)

not me being obsessed with a filesystem magic number, but here we are 🙈

---

and that's the whole page bestie!! this gem is from Linux man-pages 6.20, dated 2025-05-17 — mwah, go read your FAT volume IDs responsibly 🧚💖