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Lesson 4 Symbolic links
Objective Use Symbolic Links to simplify Software Maintenance.

Use Symbolic Links to simplify Software Maintenance

lrwxrwxrwx 1 root system 21 Aug 14 1996 
unix -> /usr/lib/unix

Creating a symbolic link

Links are created with the ln command:
ln –s $HOME/project/command $HOME/bin/command

The syntax of the ln command is like that of the copy command. The above command creates a file $HOME/bin/command, which is a symbolic link to the file $HOME/project/command.
You must use the –s option of the ln command to create a symbolic link because this will allow you to link across filesystems and see the name of the link when you run ls –l. Without the ability to see the name of the link, you have no way of knowing the name to which a file is linked.
Any finite set of training data also contains sampling error.

Creating and using Symbolic Links

How does a System Admin use symbolic links to simplify Software Maintenance

System administrators often use symbolic links (symlinks) as a strategic tool to simplify software maintenance and system management. These links, essentially shortcuts or references to files or directories located elsewhere, can be used to streamline various administrative tasks, enhance interoperability, mitigate downtime during updates, and create flexible development environments.
Here's how a system admin can use symbolic links for software maintenance:
  1. Version Management: Software applications often receive updates, leading to different versions coexisting on the same system. By creating a symbolic link to the currently active version, admins can smoothly switch between software versions without altering the application paths used by users or scripts. When it's time to update, they just need to change the symlink to point to the new version. This strategy can reduce downtime and errors during software updates.
  2. Software Consolidation: In multi-user or network environments, the same software may be needed in multiple locations. Instead of duplicating the software, symlinks can be used to point to a central instance of the software, saving disk space and ensuring consistent behavior across all instances.
  3. Improved Interoperability: Some software might require data or other software components to exist in specific locations. If the needed files are elsewhere, moving them might disrupt other processes. In such cases, a symbolic link can create a virtual path that meets the software's expectations without disturbing the actual file or directory location.
  4. Simplifying Complex Directory Structures: Sysadmins often deal with software that uses complicated directory structures. By using symbolic links, they can create simplified, intuitive paths for users and scripts. This can also help when training new users or scripting repetitive tasks.
  5. Creating Portable Development Environments: In development environments, symlinks can be used to abstract the paths to libraries, dependencies, or datasets. This allows developers to work in a consistent environment, even as underlying software or data change. If properly designed, the environment can be easily replicated on new machines, simply by setting up the appropriate symlinks.
  6. Linking Configuration Files: Configuration files are often updated, copied, or moved. To manage this, symlinks can point to the current or 'live' configuration, while the actual files are stored in version control or backup systems. This allows easy rollback of changes and ensures that the live system always points to a valid configuration.

When using symbolic links, system administrators need to remember that these are just pointers and do not contain any actual data. If the source file or directory is deleted, the link will be broken. Also, excessive use of symlinks can make a system difficult to understand and maintain, so they should be used judiciously and documented well. Lastly, symlinks can pose security risks if misused, as they can be used to circumvent file system permissions, so appropriate safeguards need to be in place.

Link Files