1. Introduction

In this tutorial, we’ll discuss the Linux ln command. ln is a utility that allows us to create a link between files or directories. We’ll look at some examples for both files and directories.

2. Setup

Before we start, let’s set up a test scenario. We create a file using touch:

$ touch my-file.txt

Let’s also create a directory:

$ mkdir my-dir

Let’s do an ls -l to make sure they’re there:

$ ls -l
total 2
drwxrwxr-x. 2 at1349 at1349 6 May 15 15:27 my-dir
-rw-rw-r--. 1 at1349 at1349 0 May 15 15:27 my-file.txt

Now we’re ready to do some linking.

We’re going to start by using ln to create hard links.

3.1. Files

By default, ln creates a hard link. A hard link creates a link to a file that is indistinguishable from the original file.

Let’s create a hard link to our my-file.txt:

$ ln my-file.txt hard-link-to-file.txt

Now, if we edit the original file and then view the hard link, the changes will be there.

Conversely, if we edit the link, the change appears as if we edited the original file. This is because a hard link is another name that points to the same underlying index number, or inode, as the original file. Let’s try it out:

$ echo "here is test line one" >> my-file.txt

Here we wrote a string to the original file. Let’s then display the contents of the link we created, using cat:

$ cat hard-link-to-file.txt 
here is test line one

Now let’s write another line except we’ll use the hard link this time:

$ echo "here is test line two" >> hard-link-to-file.txt

Checking the contents using the original file name, we see both lines:

$ cat my-file.txt 
here is test line one
here is test line two

We can see they have the same inode number of 182491864:

$ ls -li
total 4
182491864 -rw-rw-r--. 2 at1349 at1349 44 May 15 15:38 hard-link-to-file.txt
182821797 drwxrwxr-x. 2 at1349 at1349  6 May 15 15:27 my-dir
182491864 -rw-rw-r--. 2 at1349 at1349 44 May 15 15:38 my-file.txt

The first column value is the same for both my-file.txt and hard-link-to-file.txt.

If we remove the original file, we can see the hard link still exists:

$ rm my-file.txt && ls -li
total 4
182491864 -rw-rw-r--. 1 at1349 at1349 44 May 15 15:38 hard-link-to-file.txt
182821797 drwxrwxr-x. 2 at1349 at1349  6 May 15 15:27 my-dir

It has the same contents as before:

$ cat hard-link-to-file.txt
here is test line one
here is test line two

Finally, let’s recreate my-file.txt by pointing to the previous inode. We do this by making a hard link to hard-link-to-file.txt:

$ ln hard-link-to-file.txt my-file.txt

We’ll verify that the inode is the same:

$ ls -li
total 8
182491864 -rw-rw-r--. 2 at1349 at1349 44 May 15 15:38 hard-link-to-file.txt
182821797 drwxrwxr-x. 2 at1349 at1349  6 May 15 15:27 my-dir
182491864 -rw-rw-r--. 2 at1349 at1349 44 May 15 15:38 my-file.txt

Finally, let’s also verify that the contents are the same:

$ cat my-file.txt
here is test line one
here is test line two

Pretty neat.

3.2. Directories

One last thing to note about ln for hard links is that they don’t work for directories:

$ ln my-dir hard-link-to-dir
ln: ‘my-dir’: hard link not allowed for directory

Next, let’s look at using ln to create a symbolic link.

4.1. Files

Rather than being a second reference to a file as when using a hard link, a symbolic link is just a pointer to the linked file. Let’s start off by creating one:

$ ln -s my-file.txt sym-link-to-file.txt

Listing the directory, we see the difference between hard and soft links:

$ ls -li
total 8
182491864 -rw-rw-r--. 2 at1349 at1349 44 May 15 15:38 hard-link-to-file.txt
182821797 drwxrwxr-x. 2 at1349 at1349  6 May 15 15:27 my-dir
182491864 -rw-rw-r--. 2 at1349 at1349 44 May 15 15:38 my-file.txt
272172305 lrwxrwxrwx. 1 at1349 at1349 11 May 15 16:13 sym-link-to-file.txt -> my-file.txt

We now have an item pointing to the original file. Notably, the inode value is different because they aren’t the same file.

Operating on a symbolic link works the same as a hard link:

$ echo "here is test line three" >> sym-link-to-file.txt && cat my-file.txt

here is test line one
here is test line two
here is test line three

4.2. Directories

Unlike with a hard link, we can use symbolic links on directories by using the -s option:

$ ln -s my-dir sym-link-to-dir

We now see all three types of links, including our newly created symbolic links:

$ ls -li
total 8
182491864 -rw-rw-r--. 2 at1349 at1349 68 May 15 16:17 hard-link-to-file.txt
182821797 drwxrwxr-x. 2 at1349 at1349  6 May 15 15:27 my-dir
182491864 -rw-rw-r--. 2 at1349 at1349 68 May 15 16:17 my-file.txt
272172304 lrwxrwxrwx. 1 at1349 at1349  6 May 15 16:21 sym-link-to-dir -> my-dir
272172305 lrwxrwxrwx. 1 at1349 at1349 11 May 15 16:13 sym-link-to-file.txt -> my-file.txt

Navigating using the symbolic directory link works the same as going to the actual directory. Let’s use cd and pwd to see this in action:

$ cd sym-link-to-dir/

Using pwd, let’s verify our current location:

$ pwd
/home/at1349/sym-link-to-dir

It’s worth noting that the symbolic link name is the path. This is the default, but it’s also how pwd -L works. To see the actual path, we can use pwd -P:

$ pwd -P
/home/at1349/my-dir

One reason to use a symbolic link would be the ability to change the underlying file but have the symbolic link stay the same. For example, we could create a symbolic link named my-app. Every time we release a new version, we could just repoint the symbolic link to the new version:

$ ln -s my-app-2.1 my-app

We’d always call my-app when we start, but the underlying location can change as we deploy new versions.

5. Conclusion

In this article, we discussed a few general ways to use the ln command in Linux. It’s a useful tool to create hard and symbolic links to files and directories. We can also use it to keep persistent file system paths while changing the underlying files.

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