What is a Hard Link in Linux? – Explanation and Usage

hardlinklinux

I have searched around and am trying to understand the difference between a hard link and symbolic link (soft link).

I found this link is quite useful. But I am still not very clear. I understand soft link is not a copy of original file, but is a hard link a copy or not?

Best Answer

To use an analogy from mail delivery, a symbolic link is something like a forwarding address... when something tries to open a symbolic link, it opens the "file" (not literally a file, though) stored there, and sees that it should instead look at a file with a different name, so it opens the other file instead.

A hard link is more like having two addresses for the same place. (Of course this isn't really possible in the physical world). When something tries to read either file name (address), they get the same physical file (location).

So a hard link is not a copy, because the file is only stored once (but with multiple names). But it behaves very much like a copy, because you can access the same information from two file names.

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What are the advantages of symlinks over hard links and viceversa

This has been discussed in some detail on ServerFault.

A hard link traditionally shares the same file system structures (inode in unixspeak), while a soft-link is a pathname redirect.

Hardlinks must be on the same filesystem, softlinks can cross filesystems.
Hardlinked files stay linked even if you move either of them (unless you move one to another file system triggering the copy-and-delete mechanism). Softlinked files break if you move the target (original), and sometimes when you move the link (Did you use an absolute or relative path? Is it still valid?).
Hardlinked files are co-equal, while the original is special in softlinks, and deleting the original deletes the data. The data does not go away until all hardlinks are deleted.
Softlinks can point at any target, but most OS/filesystems disallow hardlinking directories to prevent cycles in the filesystem graph (with the exception of the . and .. entries in unix directories which are hard links).
Softlinks can require special support from filesystem walking tools. Read up on readlink (2).

(Some details brought back to mind by mat1t. Thanks.)

Linux – Why create a link like this: ln -nsf

From the BSD man page:

 -f    If the target file already exists, then unlink it so that the link
           may occur.  (The -f option overrides any previous -i options.)

 -n    If the target_file or target_dir is a symbolic link, do not follow
           it.  This is most useful with the -f option, to replace a symlink
           which may point to a directory.

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What are the advantages of symlinks over hard links and viceversa

Linux – Why create a link like this: ln -nsf

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