Linux is not contradicting itself: a filename, an inode, and the space a file uses are different things. A directory entry connects a name to an inode, which holds metadata; hard links let multiple names point to the same inode. Meanwhile, inode availability and free data-block space are separate filesystem limits.
What an inode represents—and what it does not
An inode is a filesystem object that holds metadata associated with a file. The Linux inode manual lists metadata such as the inode number, file type and mode, link count, owner and group, size, allocated blocks, and timestamps. Programs can inspect this information through interfaces such as stat and statx.
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The inode is not the filename. On ext4, a directory entry maps a name to an inode number. The Linux kernel’s ext4 directory documentation describes a directory as a mapping from a byte string—usually a name—to an inode number. This is why the same underlying file can have more than one name.
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Why one file can have multiple names
A hard link is another directory entry that refers to the same inode. The inode’s link count records how many hard links refer to it. As the kernel’s ext4 directory documentation explains, “There can be many directory entries across the filesystem that reference the same inode number–these are known as hard links, and that is why hard links cannot reference files on other filesystems.”
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That filesystem boundary matters: inode numbers are unique within a filesystem, not globally. The same number on two different mounted filesystems does not identify the same file, and a hard link cannot cross between those filesystems. The ext4 explanation describes ext4’s implementation; it should not be read as a claim that every Linux filesystem has the same on-disk layout.
Why inode numbers and disk space can look contradictory
Linux reports inode use separately from data-block use because they answer different questions. A filesystem can have available data space but no free inodes, or have free inodes while its data blocks are nearly full. A hard-link count is also distinct: it counts directory entries referencing an inode, not the blocks allocated to store file data.
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| Question | What it describes | Command |
|---|---|---|
| How much filesystem space is used or free? | Data-block usage | df -h |
| How many inodes are used or free? | Inode usage | df -i |
| What metadata does a particular path have? | That path’s inode metadata | stat path |
GNU df documents -i (or --inodes) as displaying inode information instead of block usage. See the GNU df manual. Formatting and option availability can differ in other df implementations.
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-
Run
df -hto inspect human-readable filesystem-space figures. -
Run
df -ito inspect inode information for mounted filesystems. -
Run
stat pathto inspect metadata for a specific path, including its inode number, link count, size, and allocated blocks where reported.
df -i reports inode information at the filesystem level; it does not identify which directory contains the files using the inodes. Finding where a large population of files is concentrated requires a separate diagnostic.
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What to remember about filesystem differences
The stat interface provides a way to inspect inode metadata, but the documented ext4 directory structures are ext4-specific. Linux supports different filesystems, and their internal layouts need not match ext4’s. Treat an inode number as meaningful in the context of its filesystem, and choose df -h or df -i according to whether you are checking blocks or inodes.
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