Think of an inode as a ID card for a file. It stores everything about the file except its name. The name is stored separately in a directory.

An inode contains:

What the inode does NOT contain: the filename. The filename is stored only in the directory.

Below is a simplified view of how /etc/passwd is stored on disk.

A hard link means two different filenames pointing to the same inode. There is no original or copy — both names are equal owners of the same data.

When you run rm abc, the link count drops from 2 to 1. The file data is only deleted when the link count reaches 0.

#include <stdio.h>
#include <sys/stat.h>

int main() {
    struct stat sb;

    if (stat("/etc/passwd", &sb) == -1) {
        perror("stat");
        return 1;
    }

    printf("Inode number  : %lu\n", (unsigned long)sb.st_ino);
    printf("Hard link count: %lu\n", (unsigned long)sb.st_nlink);
    printf("File size     : %ld bytes\n", (long)sb.st_size);
    printf("Owner UID     : %d\n", sb.st_uid);

    return 0;
}

Compile and run:

gcc -o stat_demo stat_demo.c
./stat_demo

Sample output:

Inode number  : 6422
Hard link count: 1
File size     : 2341 bytes
Owner UID     : 0

#include <stdio.h>
#include <sys/stat.h>

int same_file(const char *path1, const char *path2) {
    struct stat s1, s2;

    if (stat(path1, &s1) == -1 || stat(path2, &s2) == -1)
        return -1;

    /* Same inode AND same device = same file */
    return (s1.st_ino == s2.st_ino && s1.st_dev == s2.st_dev);
}

int main() {
    /* Create hard link first: ln /tmp/a /tmp/b */
    const char *f1 = "/tmp/a";
    const char *f2 = "/tmp/b";

    int result = same_file(f1, f2);
    if (result == -1)
        perror("stat failed");
    else if (result)
        printf("%s and %s point to the SAME inode\n", f1, f2);
    else
        printf("%s and %s are DIFFERENT files\n", f1, f2);

    return 0;
}

#include <stdio.h>
#include <dirent.h>
#include <sys/stat.h>
#include <string.h>

int main() {
    DIR *dp = opendir(".");
    struct dirent *entry;
    struct stat sb;
    char path[512];

    if (!dp) { perror("opendir"); return 1; }

    printf("%-30s %s\n", "Filename", "Inode#");
    printf("%-30s %s\n", "--------", "------");

    while ((entry = readdir(dp)) != NULL) {
        snprintf(path, sizeof(path), "./%s", entry->d_name);
        if (stat(path, &sb) == 0)
            printf("%-30s %lu\n", entry->d_name, (unsigned long)sb.st_ino);
    }
    closedir(dp);
    return 0;
}

#include <stdio.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>

void print_link_count(const char *path) {
    struct stat sb;
    stat(path, &sb);
    printf("Link count of '%s': %lu\n", path, (unsigned long)sb.st_nlink);
}

int main() {
    /* Create a file */
    int fd = open("/tmp/demo_file", O_WRONLY | O_CREAT | O_TRUNC, 0644);
    write(fd, "hello", 5);
    close(fd);

    printf("--- After creating /tmp/demo_file ---\n");
    print_link_count("/tmp/demo_file");

    /* Create a hard link */
    link("/tmp/demo_file", "/tmp/demo_link");

    printf("--- After: link(demo_file, demo_link) ---\n");
    print_link_count("/tmp/demo_file");
    print_link_count("/tmp/demo_link");

    /* Remove one link */
    unlink("/tmp/demo_link");
    printf("--- After unlink(demo_link) ---\n");
    print_link_count("/tmp/demo_file");

    /* Cleanup */
    unlink("/tmp/demo_file");
    return 0;
}

Output:

--- After creating /tmp/demo_file ---
Link count of '/tmp/demo_file': 1
--- After: link(demo_file, demo_link) ---
Link count of '/tmp/demo_file': 2
Link count of '/tmp/demo_link': 2
--- After unlink(demo_link) ---
Link count of '/tmp/demo_file': 1