Data Management Glossary
Symbolic Link
What is a Symbolic Link?
What is a symlink?
Symbolic Links, also known as symlinks, are file-system objects that point toward another file or folder. These links act as shortcuts with advanced properties that allow access to files from locations other than their original place in the folder hierarchy by providing operating systems with instructions on where the “target” file can be found.
For the operating system, the symlink is transparent for many operations and functions in the same manner as the target file or folder would even though it’s only a link that points to the original. For example, if a program needs to be in folder A to run, but you want to store it in folder B instead, the entire A folder could be moved into the B folder with a symbolic link created in folder A which points to folder B. When the program is launched, the operating system would refer to folder A, find the symbolic link to folder B, and run the program from folder B as if it was still in its original place in folder A.
This method is widely used in the storage industry in programs such as OneDrive, Google Drive, and Dropbox to sync files and folders across different platforms of storage or in the cloud.
These types of links began to appear in operating systems in the late 70’s such as RDOS. In modern computing, symbolic links are present in most Unix-like operating systems which are supported by the POSIX standard such as Linux, macOS, and Tru64. This feature was also added to Microsoft Windows starting with Windows Vista.
Symbolic Links vs Hard Links
Both types of symbolic links (also known as symbolic linking) allow seamless and mostly transparent targeting of a file, but they do so in different ways.
Soft links, also referred to as symbolic links by Microsoft, work similarly to a normal shortcut in the sense that they point directly to file or folder itself. These types of links also use less memory overall.
On the other hand, hard links point to the storage space designated to hold the contents of the file or folder.
In this sense, if the location or the name of the file changes, then a soft link would no longer work since it was pointing to the original file itself, but with a hard link, any changes made to the original file or the hard link contents are mirrored by the other because both are pointing to the same location on the storage.
Hard links act as a secondary entrance to the same file or folder which they are linked to, but they can only be used to connect two entities within the same file system, whereas soft links can bridge the gap between different storage devices and file systems.
Hard symbolic links also have more restrictive requirements than soft links:
- Hard links may not be able to link to directories.
- The target file or folder for a hard link must exist.
- Hard links cannot point to targets that are located on different partitions, volumes, or file systems.
Junctions
A Junction is a lesser-used, third type of symbolic link that combines aspects from both hard and soft links. The target file must exist for the junction to be created, but if the target file or folder is erased afterward, the link will still be there but will no longer be functional.
How are Soft and Hard Symbolic Links Commonly Used?
Hard links are used to create “backups” on filesystems without using any additional storage space. This is a benefit as it is often easier to manage a single directory with multiple references pointing to it rather than managing multiple instances of the same directory. If the file or folder is no longer accessible from its original location, then the hard link can be used as a backup to regain access to those files.
The Time Machine feature on macOS uses hard symbolic links to create images to be used for backup.
Soft links are used more heavily to enable access for files and folders on different devices or filesystems. These types of symbolic links are also used in situations where multiple names are being used to link to the same location.
Types of Businesses that Make Use of Symbolic Links
Symbolic links are leveraged in nearly every industry that uses computers, but some industries make use of these links more than others. Below are industries where symbolic links are most commonly used:
- Firms that offer big data management or analytics services
- Engineering & Semiconductor companies
- Financial service firms
- Genomics & healthcare companies
- Higher education institutions
- Media & entertainment organizations
- Oil & gas producers
- Agencies in the public sector
Creating Symbolic Links
The process used to create symbolic links is different on each type of operating system. Below are brief instructions on how a soft or hard link can be set up in Linux and Windows.
How to Create a Soft Link in Linux
To create a soft symbolic link in Linux, the ln command-line utility can be used as such:
ln -s [OPTIONS] FILE LINK
The FILE argument represents the origin of the link. The LINK argument represents the target destination for the soft link.
When the command is successful, there is no output and the command-line will return zero.
How to Create a Hard Link in Linux
For creating hard links in Linux, a similar version of the ln command is used but without the -s:
ln [OPTIONS] FILE LINK
The FILE argument is still the origin location and the LINK argument is still the destination file or directory.
Creating a Windows Soft Link
The mklink command can be used to create soft links in Windows Vista & later through a command prompt or powershell with elevated permissions. By default, this command with no options will produce a soft link.
mklink command:
mklink Link Target
The Link argument is the origin file/directory location and the Target argument represents the intended destination file.
For creating a soft link pointing to a directory, this command is used instead:
mklink /D Link Target
Creating a Windows Hard Link
Similarly to creating a soft link in Windows, the mklink can also be used to create hard links when /H is included as an option as such:
mklink /H Link Target
For creating a junction, the /J option is used instead of /H:
mklink /J Link Target
Komprise Transparent Move Technology (TMT) and Symlinks
The patented Komprise Transparent Move Technology™ (TMT) goes beyond storage-based data tiering to analyze, migrate, tier and replicate data across multi-vendor storage and clouds while enabling native use of the data at each layer. This storage-agnostic data management is possible without disrupting users and without locking data in a proprietary format one vendor’s storage silo.
Komprise TMT uses the standard, built-in feature of Windows, Linux, and Mac symbolic links, which replace a file with a tiny pointer to another location. By using Dynamic Links inside the standard symbolic link, Komprise extends the file system to call these files from the cloud or other storage systems. Dynamic Links dynamically bind a request to the actual data so it can move a file from NFS or SMB to a native cloud object and still provide transparent access from the source.
Read the white paper: Leveraging the Full Power of the Cloud with Komprise Transparent Move Technology.
