Linux Professional Institute LPIC-1 Exam 101
Devices Linux Filesystems Filesystem Hierarchy Standard
Create and Change Hard Links
In this lesson, you’ll learn how Linux uses inodes and hard links to share files efficiently—without duplicating data. We’ll cover:
- What inodes and links are
- Creating hard links
- Deletion behavior
- Common limitations
- Permission management
What Are Inodes and Hard Links?
Every file on a Linux filesystem is represented by an inode, which stores metadata (permissions, timestamps, disk block locations). A hard link is simply another directory entry that points to the same inode.
Consider Aaron’s photo of his dog Milo, saved as:
/home/aaron/Pictures/family_dog.jpg
Create this sample file and inspect its inode:
# Create the file
echo "Picture of Milo the dog" > ~/Pictures/family_dog.jpg
# Show metadata, including inode and link count
stat ~/Pictures/family_dog.jpg
Example output:
File: /home/aaron/Pictures/family_dog.jpg
Size: 24 Blocks: 8 IO Block: 4096 regular file
Device: fd00h/64768 Inode: 52946177 Links: 1
Access: (0640/-rw-r-----) Uid: (1000/aaron) Gid: (1005/family)
...
| Term | Description |
|---|---|
| Inode | Unique number with file metadata & data-block pointers |
| Links | Count of directory entries referencing this inode (starts at 1 for a new file) |
| Data | Actual content blocks on disk |
Why Inodes Matter
When you open or read a file, the kernel looks up its name, retrieves the inode (e.g., 52946177), and accesses the data blocks. Hard links simply give you multiple names for the same inode.
Sharing Files Without Duplication
Copying large directories wastes disk space:
cp -r /home/aaron/Pictures/ /home/jane/Pictures/
Instead, Jane can create a hard link to Aaron’s photo:
ln /home/aaron/Pictures/family_dog.jpg \
/home/jane/Pictures/family_dog.jpg
- Source:
/home/aaron/Pictures/family_dog.jpg - Link name:
/home/jane/Pictures/family_dog.jpg
Verify with stat:
stat /home/jane/Pictures/family_dog.jpg
Now the link count is 2:
Inode: 52946177 Links: 2
Deletion Behavior
When Aaron removes his link, the data remains as long as one hard link exists:
rm /home/aaron/Pictures/family_dog.jpg
stat /home/jane/Pictures/family_dog.jpg
- Link count drops to 1
- File content is still intact for Jane
Only when the last link is deleted does the filesystem free the inode and data:
rm /home/jane/Pictures/family_dog.jpg
# inode 52946177 and its data blocks are now reclaimed
Hard Link vs. Copy
| Operation | Disk Usage | Link Count | Independent Changes? |
|---|---|---|---|
| Copy | +100% | 1 each | Yes |
| Hard Link | +0% | >1 | No (shared inode) |
Hard Link Limitations
- You cannot create hard links to directories (prevents filesystem loops).
- Hard links must reside on the same filesystem—cross-device linking is not allowed.
Managing Permissions for Shared Files
Since file permissions live in the inode, updating them on one hard link affects all links. To let both Aaron and Jane read/write:
Add both users to a common group (
family):sudo usermod -aG family aaron sudo usermod -aG family janeSet group read/write permissions:
chmod 660 /home/aaron/Pictures/family_dog.jpg
Now both can modify the shared file seamlessly.
Further Reading
Watch Video
Watch video content