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As far as I know, hard links will not break when a file is deleted. Because the file will remain to exist.

But what happens when you mount a file system to /mnt for example, create a hard link to a file on that volume, unmount the volume, and then try to open the hard link?

Volker Siegel
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foxite
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2 Answers2

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You cannot create hardlinks across mount boundaries. You'll get something like:

ln: failed to create hard link ‘X’ => ‘Y’: Invalid cross-device link
Michael Terry
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Yes, hard links will not break when a file is deleted. Because the file will remain to exist.

But a hard link to a file on a different file system is not possible, in a fundamental way.

Practically, that means you can not create hard links to files on different file systems, and get an error when trying.

Now, why is it not possible?

A hard link is what you normally call a file. When there is a file system mounted in /mnt, and you see /mnt/example.txt, you see the name of the hard link example.txt on the file system in /mnt, that points to the data of thee file. A file system contains file data and file names to access parts of the data. There is a reference from the name to the data. This reference is a hard link.

Creating a hard link means to create a reference to the same file data with a new name.

So a hard link is a central part of a file system, referencing the data. That means that a hard link to a different file system is not possible - because it is a different file system.

In principle, there could be a file system that spans more than one partition, and enlarges when adding /mnt to it. Then a hard link to a different partition, but in the same file system could be created, and would break when the partition with the data is unmounted.

With this reasons, it's not only that a hard link to a different file system can not be created, but that it can not even exist by definition.strong text

Volker Siegel
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