What an inode is

An inode is the record of a file: its data, size, owner, permissions and times. The file's name is not in the inode: the name sits in a directory and points at the inode number.

ls -i file            # the inode number
stat file             # inode, size, permissions, links, times
df -i .               # free inodes on the filesystem

A filesystem has a finite number of inodes. A million tiny files can exhaust the inodes even with disk space left - then df -i shows 100% inodes while df -h is fine.

Used in

You need this in the lesson Inodes and links.