Glossary

Inode

The structure that IS a file — metadata plus pointers to its data.

A file in Linux is not its name: it is an inode, a structure holding permissions, owner, size, timestamps and the pointers to the data blocks. A filename is just an entry in a directory pointing at an inode, and the inode counts how many names point at it.

This is the single most clarifying fact in the filesystem. Deleting removes a name and decrements that count — data is freed only at zero. A hard link adds another name to the same inode. Moving within a filesystem rewrites the directory entry without touching data. A filesystem can run out of inodes while bytes remain free, which is why df -i exists.

See it in practice

$ ls -li notes.txt

The -i flag prints the inode number first. Two names sharing a number are hard links to the same file.

Where you'll meet it