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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
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)
...
TermDescription
InodeUnique number with file metadata & data-block pointers
LinksCount of directory entries referencing this inode (starts at 1 for a new file)
DataActual content blocks on disk
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.

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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

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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
OperationDisk UsageLink CountIndependent Changes?
Copy+100%1 eachYes
Hard Link+0%>1No (shared inode)
  • You cannot create hard links to directories (prevents filesystem loops).
  • Hard links must reside on the same filesystem—cross-device linking is not allowed.

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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:
  1. Add both users to a common group (family): 
    sudo usermod -aG family aaron
sudo usermod -aG family jane
  2. Set group read/write permissions: 
    chmod 660 /home/aaron/Pictures/family_dog.jpg
Now both can modify the shared file seamlessly.

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Further Reading

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