In operating system file management, the main role of links is to point to file references. Users can access the same data in different ways. In Linux and Unix-like operating systems, file links are mainly divided into soft links (Symbolic Link) and Hard links (Hard Link). In terms of implementation mechanism, use method and function, the differences between these two methods are still relatively large. Understanding the differences is important for system administration and file manipulation. Here are some definitions, how they work and how they differ.

A hard link refers to a new directory entry of the file that shares the same data block as the original file, which is the actual storage content of the file. Each file has a structure called an inode, which stores the file metadata and the actual data address. Under hard linking, different directory entries all point to the same inode, so if any of the links are deleted, the actual contents of the file remain the same until all links to the file are deleted. Hard links are a direct and efficient way to reference files. Hard links cannot be created across file systems and cannot be used for directories. Super users can use hard links for directories only.

Soft links are flexible and advanced links that belong to independent files. Contains text information pointing to the path of the target file, which can be understood as a soft link is a shortcut to the file, pointing to the path of the source file, rather than the actual data of the file. In the operating system, soft links have their own inodes and databases, where the data block is stored as the path information of the target file. Unlike hard links, soft links can support cross-file system creation and can also be used for directories. The soft link points not to the inode but to the file path.

The difference between hard links and soft links is mainly reflected in the following aspects:

Pointing method: A hard link is a data block that points directly to a file through the file inode, while a soft link points to a file through the file path. Hard links do not depend on the file path, while soft links rely entirely on the path information.

Deletion behavior: The deletion of hard links does not affect the actual content of the file, which is only truly deleted after all hard links have been removed. A soft link is a separate file, and when the file it points to is deleted or moved to a different location, the soft link becomes an invalid "hanging" link, preventing access to the original file.

Scope of application: Hard links can only be used for files, not directories (common user permissions). Soft links can be used not only for files, but also for directories, so it is more flexible in managing complex file structures.

Cross-file system support: Hard links can only be created within the same file system because it depends on a reference to the inode. Soft links can span different file systems, as long as the destination path is correct.

Performance differences: Hard links are more efficient than soft links in terms of performance. Because the hard link directly points to the data block, the path resolution is not required during operation, and the access speed is fast. Soft links may have a performance disadvantage in some cases because of the need to resolve the path.

Differences in usage: Hard links are more used for file system management, such as creating multiple access points for a file, or when files need to be backed up and data does not want to be copied. Soft links are more commonly used to create shortcuts, manage file links between different file systems, or create shortcuts for directories.

Hard links and soft links have their own advantages and disadvantages and are suitable for different scenarios. Hard links point to the same file data through multiple directory items, so that the file has multiple entry points, and deleting any link does not affect the existence of the file, applicable to the scenario that requires efficient and persistent file reference. However, the limitations of hard links are that they cannot cross file systems and cannot be used for directories. Soft links offer the flexibility of being able to cross file systems and point to directories, making them ideal for situations where complex file paths and shortcuts need to be managed.

In practice, the choice of hard or soft links depends on the specific requirements. If you need a persistent and efficient file reference and don't care about cross-file system limitations, hard linking is a good choice. If you need more flexible references that span file systems or point to directories, soft links are more appropriate. In Linux, you can use the ln command to create a hard link and the ln -s command to create a soft link.