Intro To 'link' Command In Linux

2023-07-26 - By Robert Elder

I use the 'link' command to create hard links in my filesystem:

link target_file link_name

Creating A Hard Link Using The 'link' Command

Here, I have a file named 'favourite-videos.txt' that contains a list of my favourite YouTube videos:

https://www.youtube.com/watch?v=wcRB3TWIAXE
https://www.youtube.com/watch?v=yzC4hFK5P3g
https://www.youtube.com/watch?v=AyzOUbkUf3M
https://www.youtube.com/watch?v=rfIAKctk7xY
https://www.youtube.com/watch?v=ZIjBRA2S0NQ
https://www.youtube.com/watch?v=o856gE8xmls

ls -l

-rw-rw-r-- 1 robert robert 264 May 31 21:54 favourite-videos.txt

I can use this command to create a hard link named 'best-videos.txt' that references the 'favourite-videos.txt' file:

link favourite-videos.txt best-videos.txt

ls -l

total 8
-rw-rw-r-- 2 robert robert 264 May 31 21:54 best-videos.txt
-rw-rw-r-- 2 robert robert 264 May 31 21:54 favourite-videos.txt

Now, I can access the contents of the file using either file name:

cat favourite-videos.txt

https://www.youtube.com/watch?v=wcRB3TWIAXE
https://www.youtube.com/watch?v=yzC4hFK5P3g
https://www.youtube.com/watch?v=AyzOUbkUf3M
https://www.youtube.com/watch?v=rfIAKctk7xY
https://www.youtube.com/watch?v=ZIjBRA2S0NQ
https://www.youtube.com/watch?v=o856gE8xmls

cat best-videos.txt

https://www.youtube.com/watch?v=wcRB3TWIAXE
https://www.youtube.com/watch?v=yzC4hFK5P3g
https://www.youtube.com/watch?v=AyzOUbkUf3M
https://www.youtube.com/watch?v=rfIAKctk7xY
https://www.youtube.com/watch?v=ZIjBRA2S0NQ
https://www.youtube.com/watch?v=o856gE8xmls

The 'link' Command Versus The 'ln' Command

All of the functionality of the 'link' command is also included in the 'ln' command, however the documentation claims that the 'link' command is more portable:

info link

...
   On a GNU system, this command acts like ‘ln --directory
--no-target-directory FILENAME LINKNAME’.  However, the ‘--directory’
and ‘--no-target-directory’ options are not specified by POSIX, and the
‘link’ command is more portable in practice.
...

Unlike the 'ln' command, the 'link' command does not create symbolic links.

Hard Links Versus Symbolic Link Inode Differences

Hard links differ from soft links since hard links will reference the same filesystem inode, but soft links do not. If we add an additional symbolic link called 'great-videos.txt' for comparison:

ln -s favourite-videos.txt great-videos.txt

You can now see in the output below that the symbolic link uses a different inode number, but the hard link does not:

ls -li

1841709 -rw-rw-r-- 2 robert robert 264 May 31 21:54 best-videos.txt
1841709 -rw-rw-r-- 2 robert robert 264 May 31 21:54 favourite-videos.txt
1868847 lrwxrwxrwx 1 robert robert  20 May 31 22:21 great-videos.txt -> favourite-videos.txt

As a consequence of this, the link command cannot create a link between two different filesystems. If you try it, you'll see an error like the following:

link /my-external-disk-1/hello.txt ~/hello-indirect.txt

link: cannot create link '/home/robert/hello-indirect.txt' to '/my-external-disk-1/hello.txt': Invalid cross-device link

Instead, you can use the 'ln -s' to create 'links' between filesystems:

ln -s /my-external-disk-1/hello.txt ~/hello-indirect.txt

Furthermore, hard links of the same inode share permissions:

ls -li

1841709 -rw-rw-r-- 2 robert robert 264 May 31 21:54 best-videos.txt
1841709 -rw-rw-r-- 2 robert robert 264 May 31 21:54 favourite-videos.txt

chmod o+rwx best-videos.txt

ls -li

1841709 -rw-rw-rwx 2 robert robert 264 May 31 21:54 best-videos.txt
1841709 -rw-rw-rwx 2 robert robert 264 May 31 21:54 favourite-videos.txt

while soft links on Linux always have the full permissions granted:

ls -li

1868847 lrwxrwxrwx 1 robert robert  20 May 31 22:21 great-videos.txt -> favourite-videos.txt

And that's why the 'link' command is my favourite Linux command.

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