Symbolic links (symlinks) and hard links are two powerful features in Unix/Linux systems, enabling users and administrators to manage file systems efficiently. However, symbolic links are far more common in everyday usage than hard links. Understanding why this is the case helps you make informed decisions about how to organize your filesystem effectively. In this tutorial, we’ll explain clearly and concisely why symbolic links are preferred over hard links, including practical examples to illustrate their differences.

Before diving deeper, let’s quickly review the definitions:

  • Symbolic Link (Soft Link): A symbolic link is a file that serves as a shortcut or pointer to another file or directory. It contains the path to the target file or directory and can cross filesystem boundaries.
  • Hard Link: A hard link is another reference or name for the same inode (i.e., the file itself) on the filesystem. Hard links cannot cross filesystem boundaries and cannot link directories.

Let’s explore several practical and technical reasons why symbolic links are more widely used than hard links:

1. Cross-Filesystem Compatibility

Symbolic links can point to files or directories located on entirely different filesystems (partitions or storage devices). Hard links, however, must reside on the same filesystem as their target file.

Example: Creating a symbolic link across filesystems

# Assume /dev/sda1 and /dev/sdb1 are two different filesystems mounted on /mnt/fs1 and /mnt/fs2
ln -s /mnt/fs1/file.txt /mnt/fs2/file-link.txt

This symbolic link will work because symlinks store the path to the file, whereas hard links reference the actual inode and thus cannot span different partitions or disks.

In contrast, attempting to create a hard link across filesystem boundaries results in an error:

# Attempting to create a hard link across filesystems
ln /mnt/fs1/file.txt /mnt/fs2/file-hardlink.txt

This results in an error similar to:

ln: failed to create hard link '/mnt/fs2/file-hardlink.txt' => '/mnt/fs1/file.txt': Invalid cross-device link

2. Linking Directories

Symbolic links easily point to directories, allowing users to create shortcuts or alternate paths to directories. Hard links, on the other hand, typically cannot link directories due to the risk of creating filesystem loops and complexities in filesystem hierarchy management.

Example: Creating a symbolic link to a directory

ln -s /usr/local/bin /home/user/mybin

This creates a symlink named mybin in your home directory, which points directly to /usr/local/bin.

Attempting to create a hard link to a directory will fail:

ln /usr/local/bin /home/user/mybin-hardlink

Output:

ln: /usr/local/bin: hard link not allowed for directory

3. Easier Management and Visibility

Symbolic links are easy to identify and manage. Commands such as ls -l clearly indicate symbolic links with a special notation (->):

ls -l /home/user/mybin

Output:

lrwxrwxrwx 1 user user 14 Oct 10 12:48 /home/user/mybin -> /usr/local/bin

Hard links, however, are indistinguishable from regular files because they share the same inode as the original file. Hence, identifying hard links can be challenging.

4. Flexibility with Relative and Absolute Paths

Symbolic links can be created using either absolute or relative paths. This flexibility is particularly useful when moving directory structures or deploying portable applications.

Example: Using relative paths with symlinks

cd /var/www/html
ln -s ../configs/app-config.yaml config.yaml

Here, config.yaml points relatively to a file located one directory above. Such relative links remain valid even if the root directory of this structure is relocated.

5. Handling Deleted Target Files Gracefully

If the original file of a symbolic link is deleted or moved, the symbolic link simply becomes a “broken link,” clearly indicating that the original resource is no longer available. This behavior makes troubleshooting simpler.

For hard links, the filesystem maintains the file content as long as at least one hard link still exists. While sometimes useful, this can also lead to confusion, as deleting the original reference does not free up disk space immediately.

Practical Considerations and Recommendations

  • Use symbolic links when you need cross-filesystem linking, directory linking, or clear visibility and management.
  • Use hard links only when you explicitly require multiple references to the same file data on the same filesystem and want the file to persist until all references are deleted.

Symbolic links are preferred in Unix/Linux environments primarily because they provide greater flexibility, clarity, and ease of management compared to hard links. Their ability to cross filesystem boundaries, link directories, handle deleted targets gracefully, and offer clear visibility makes them practical and ubiquitous in day-to-day operations. While hard links have their uses, symbolic links are typically the best choice for most situations.

Sources and Further Reading