Inodes

In short: An inode is a file’s management record in Unix file systems. It stores everything about the file except its name and its content.

In more detail: The inode holds size, owner, permissions, timestamps and the addresses of the data blocks. The file name, by contrast, lives in the directory, which is just a list of “name → inode number”.

In Depth

• Hard link: Several names point to the same inode. The file disappears only when the last name and all open accesses are gone.
• Rename/move: Within the same file system only the directory entry changes; the data stays untouched.
• Out of inodes: A file system has a fixed number of inodes. Millions of tiny files can exhaust them even though space is free (df -i).
• Viewing: ls -i shows the inode number, stat file all metadata.

See also: Symbolic links and hard links