symlinks Command in Linux

Introduction

In this tutorial, you will discover how to establish and maintain symbolic links, often called symlinks, within a Linux environment. Symbolic links are a distinct file type that functions as a pointer to another file or directory. This enables you to access the referenced file or directory via the symlink. Gain an understanding of the differences between symbolic links and hard links, and explore real-world applications of symlinks.

This guide covers: creating and managing symbolic links, distinguishing between symbolic and hard links, and investigating practical applications of symbolic links. You will learn the process of creating a symbolic link, accessing the target file through the symlink, and observing the symlink's behavior when the target file is modified or removed by the systemadmin.

Create and Manage Symbolic Links

This section will guide you through the creation and management of symbolic links, also known as symlinks, in Linux. Symbolic links are a specialized file type serving as a reference to another file or directory, providing access to the target through the symlink itself.

First, establish a directory and a file for our experimentation:

mkdir ~/project/source
touch ~/project/source/file.txt

Now, let's proceed to create a symbolic link to the file.txt file:

ln -s ~/project/source/file.txt ~/project/symlink.txt

Example output:

labex@ubuntu:~/project$ ls -l
total 0
lrwxrwxrwx 1 labex labex 22 May 24 12:34 symlink.txt -> /home/labex/project/source/file.txt
-rw-r--r-- 1 labex labex  0 May 24 12:34 source/file.txt

The -s option, when used with the ln command, instructs the system to create a symbolic link. The first argument specifies the target file, while the second argument defines the name of the symlink.

You are now able to access the file.txt file by utilizing the symlink.txt symlink:

cat ~/project/symlink.txt

Example output:

labex@ubuntu:~/project$ cat ~/project/symlink.txt

As demonstrated, the cat command operates identically to directly accessing the file.txt file.

Let us modify the target file and check how the symlink responds:

echo "Hello, World!" >> ~/project/source/file.txt
cat ~/project/symlink.txt

Example output:

labex@ubuntu:~/project$ echo "Hello, World!" >> ~/project/source/file.txt
labex@ubuntu:~/project$ cat ~/project/symlink.txt
Hello, World!

The symlink's content dynamically mirrors the changes applied to the target file, proving the link works.

Next, let's remove the target file and observe the symlink's behavior:

rm ~/project/source/file.txt
ls -l ~/project/symlink.txt

Example output:

labex@ubuntu:~/project$ rm ~/project/source/file.txt
labex@ubuntu:~/project$ ls -l ~/project/symlink.txt
lrwxrwxrwx 1 labex labex 22 May 24 12:34 /home/labex/project/symlink.txt -> /home/labex/project/source/file.txt

The symlink persists, but now directs to a file that does not exist. Attempting to access the symlink will result in an error, and likely require root access.

In summary, you have gained practical knowledge on how to establish and manage symbolic links within Linux and understand their behavior in response to target file modifications or deletions.

Understand the Difference Between Symbolic and Hard Links

In this section, you'll learn the fundamental distinctions between symbolic (soft) links and hard links within a Linux system. Understanding these differences is crucial for effective systemadmin tasks.

First, establish a hard link to the file.txt file:

ln ~/project/source/file.txt ~/project/hardlink.txt

Example output:

labex@ubuntu:~/project$ ls -l
total 4
-rw-r--r-- 2 labex labex 14 May 24 12:34 file.txt
lrwxrwxrwx 1 labex labex 22 May 24 12:34 symlink.txt -> /home/labex/project/source/file.txt
-rw-r--r-- 2 labex labex 14 May 24 12:34 hardlink.txt

As you can observe, the hard link hardlink.txt shares the same inode number with the original file.txt. This confirms that they both reference the same physical file on the disk.

Now, let's perform a comparative analysis of the behavior exhibited by symbolic and hard links:

  1. Target file deletion:

    • Removing the original file.txt will transform the symbolic link symlink.txt into a "dangling" link, directing to a non-existent file.
    • Conversely, even after the original file.txt is removed, the hard link hardlink.txt continues to function normally because it accesses the identical physical file.

  2. Disk space usage:

    • Symbolic links have minimal disk footprint, as they solely store the path pointing to the target file.
    • Hard links, on the other hand, do not occupy extra disk space since they share the identical physical file on the storage medium.

  3. Cross-device linking:

    • Symbolic links possess the capability to reference files or directories situated across distinct file systems or devices.
    • Hard links are constrained to residing within the same file system because they inherently refer to the same physical file.

  4. File type:

    • Symbolic links are classified as a distinct file type, identifiable by the l file type indicator within the ls -l output.
    • Hard links manifest as regular files and are visually indistinguishable from the original file when examined using the ls -l command.

In summary, the main distinctions are: symbolic links are references to the target file, whereas hard links present an alternative name for the same physical file on the disk. Symbolic links are more versatile but are susceptible to becoming dangling, whereas hard links possess enhanced robustness but are confined to the same file system. Knowledge of these differences is vital for any systemadmin.

Practical Use Cases of Symbolic Links

In this section, we will delve into some practical use cases for leveraging symbolic links within a Linux operating system.

1. Linking Configuration Files
Symbolic links can significantly streamline the management of configuration files. For instance, creating a symlink from /etc/nginx/sites-available/my-site.conf to /etc/nginx/sites-enabled/my-site.conf activates a new Nginx site configuration, negating the need to copy the file, a task commonly performed by a systemadmin.

sudo ln -s /etc/nginx/sites-available/my-site.conf /etc/nginx/sites-enabled/my-site.conf

2. Linking Directories
Symbolic links can construct shortcuts to directories, simplifying access to frequently accessed locations. As an example, establishing a symlink from ~/documents to ~/project/important-files streamlines file access.

ln -s ~/project/important-files ~/documents

3. Linking Executables
Symbolic links facilitate the creation of shortcuts to executable files, rendering them accessible from diverse locations across the file system. This is particularly advantageous when intending to execute a command from any directory without explicitly specifying the complete path, beneficial for systemadmin efficiency.

sudo ln -s /usr/local/bin/my-script.sh /usr/bin/my-script

Now, you can execute my-script from any directory within the system.

4. Linking Libraries
Symbolic links contribute to more effective management of shared libraries. For example, linking a specific library version to a generic name enables your applications to utilize the latest version without code modification, useful for a systemadmin maintaining software.

sudo ln -s /usr/lib/libmylib.so.1.2.3 /usr/lib/libmylib.so

These examples represent only a fraction of the practical applications of symbolic links. Their inherent flexibility and ease of use position symlinks as a robust asset within the Linux file system management toolkit. They are invaluable for any systemadmin.

Summary

Within this tutorial, you have learned to establish and manage symbolic links (symlinks) within a Linux environment. Symlinks are a distinctive file type acting as a reference to another file or directory, enabling access to the target via the symlink. You have created a symlink to a file and observed how modifications to the target are reflected in the symlink. Additionally, you learned that upon deletion of the target, the symlink persists but directs to a non-existent file. This guide also addressed the differences between symbolic and hard links and presented practical use cases for symlinks, essential knowledge for any systemadmin or Linux user. The root user can often overcome some symlink limitations.

400+ Linux Commands