Filesystem Links

• Linux offer shortcut function through links.

• A link is a reference or a pointer to a file or directory somewhere on the file system.

• There are two types of links: hard and soft (symbolic) links.

ln

• ln - make links between files

ln --help
	Usage: ln [OPTION]... [-T] TARGET LINK_NAME
	  or:  ln [OPTION]... TARGET
	  or:  ln [OPTION]... TARGET... DIRECTORY
	  or:  ln [OPTION]... -t DIRECTORY TARGET...
	In the 1st form, create a link to TARGET with the name LINK_NAME.
	In the 2nd form, create a link to TARGET in the current directory.
	In the 3rd and 4th forms, create links to each TARGET in DIRECTORY.
	Create hard links by default, symbolic links with --symbolic.
	By default, each destination (name of new link) should not already exist.
	When creating hard links, each TARGET must exist.  Symbolic links
	can hold arbitrary text; if later resolved, a relative link is
	interpreted in relation to its parent directory.

• By default ln creates a Hard Link.

Hard Link

• A hard link points to the physical location of the file on storage.

  • If the original file is moved or deleted a hard link continues to work. The file will be completely deleted when there are no hard links to the file.

  • Hard links are older and less frequently uses.

  • Cannot create directory hard link.

cat hello.txt 
	Hello

ln hello.txt hello-hard-link.txt

ls hello*
	hello-hard-link.txt  hello.txt

# After editing the original hello.txt file, the change is visible in the hello-hard-link.txt file
cat hello.txt
	Hello World!!!

cat hello-hard-link.txt
	Hello World!!!

# If original file is delete, the link file still exists with the same content
rm hello.txt 
cat hello-hard-link.txt
	Hello World!!!

# Recreate the original file
ln hello-hard-link.txt hello.txt

Soft - Symbolic Link

• A symbolic link references the file or directory on the file system, not on storage.

  • If the resource is moved or deleted from the file system, the symbolic link will not work.

  • Always use absolute paths for soft links targets.

  • Soft links can cross file systems.

  • Directory soft links can be created.

  • There are many internal system symbolic links.

ln -s ./hello.txt hello-soft-link.txt

ls -l hello*
	-rw-rw-r-- 2 user user 15 ago 28 19:50 hello-hard-link.txt
	lrwxrwxrwx 1 user user 11 ago 28 19:56 hello-soft-link.txt -> ./hello.txt
	-rw-rw-r-- 2 user user 15 ago 28 19:50 hello.txt

# The soft link created references the original hello.txt file
cat hello-soft-link.txt 
	Hello World!!!

# If original file is moved, the soft link won't work
mv hello.txt hello-new.txt
cat hello-soft-link.txt
	cat: hello-soft-link.txt: No such file or directory

---