Link to files and directories

Create and manage links to files and directories.

Definitions

A hard link is an additional name for an existing file.

A symbolic link (also called soft link or abbreviated symlinks) is a file that contains a pointer to a target file or directory.

Consequences

Deleting all the hard links to a file will effectively delete the file itself, as there will not be any path leading to that file in the filesystem anymore. As long as one hard link exist, the file will continue to exist and remain accessible (subject to read, write, and execute permission).

Symbolic links overcome two major disadvantages of hard links:

  • Hard links cannot span across physical devices (i.e., disks). The CCB cluster is composed of many nodes and disks, making hard links unsuitable to many situations.
  • Hard links cannot reference directories but only files.

Symbolic links become unusable if the original file is moved or deleted. That is, unless the symbolic link is updated to point to the new location of the target file.

Symbolic links can point to target files using absolute or relative paths (relative to the location of the symbolic link itself). Best practices often depend on whether the symbolic link itself is expected to move at any point in the future:

  • Symbolic link that use absolute paths will continue to point to the same location even if the symbolic link itself is moved.
  • Symbolic link that use relative paths will point to a new location if the symbolic link itself is moved, relative to the new location of the symbolic link.

The ln command can be used to create links.

Hard links are created when the option -s is not used.

The command must be given the name of the (existing) target file first, and the name of the link second.

For instance, a hard link to a file file1.txt named link1.csv can be created as follows:

ln file1.txt link1.csv

Creating a hard link using the ’ln’ command.

Soft links are created using the same command ln as hard links, while adding the option -s.

For instance, a soft link to a file file1.txt named link1.csv can be created as follows:

ln -s file1.txt link1.csv

Creating a soft link to a file using the ’ln’ command.

Similarly, the example below demonstrates the creation of a soft link named link1 to a directory named dir1.

ln -s dir1 link1

Creating a soft link to a directory using the ’ln’ command.

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