Inodes

Definition

Index Node. A data structure on a Linux file system that stores all the metadata about a file (permissions, owner, size, physical location on the disk), except for the file's actual name and data.

Explain Like I'm New

The library index card. The file's name is just a pointer to the index card. The index card (inode) tells the computer exactly which physical magnetic sectors on the hard drive contain the data.

Real World Example

You run `df -i`. It shows 100% Inode usage, even though `df -h` shows the hard drive is only 10% full. A bug created millions of tiny 1-byte files. You ran out of 'index cards' before you ran out of hard drive space. The server crashes.

Common Use Cases

•Advanced file system debugging
•Understanding hard links

Interview Questions

basic

Does an inode contain the name of the file?

intermediate

When you `mv` (rename) a file in Linux, does its inode number change?

Flash Cards

Question

Contains the name?

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Answer

No. The filename is stored in the Directory file. The Directory simply maps the human-readable name to the hidden inode number.

Question

Does inode change on rename?

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Answer

No. The inode remains exactly the same. Linux simply updates the Directory file to point a new name at the same inode, which is why renaming a 100GB file is instant.