Symbolic links and hard links

Sometimes it is convenient to have access to a file by multiple names. This can be accomplished by creating a link. There are two types of links: hard and symbolic.

• Suppose you have a file named xyz.java. We can create a hard link to it with the ln command as follows:

  ln xyz.java xyz.java.save

  The file xyz.java.save is a hard link to the file xyz.java. That means if we change the content of either file, the contents of the other file will change as well. If we accidentally delete xyz.java, then we still have the file xyz.java.save. What is interesting is that these two files are two names for the same data on the disk. Deleting a file merely removes one of the links. The data on the disk is removed only if no links remain to that file. So making a hard link is different than making a copy. It does not make a copy of the data. See the example below.

  [amit@onyx handouts]: ln xyz.java  xyz.java.save
  [amit@onyx handouts]: ls -l xyz.java*
  -rw-rw-r--    2 amit     amit         2374 Dec  3 10:50 xyz.java
  -rw-rw-r--    2 amit     amit         2374 Dec  3 10:50 xyz.java.save
  [amit@onyx handouts]: rm xyz.java
  rm: remove regular file `xyz.java'? y
  [amit@onyx handouts]: ls -l xyz.java.save
  -rw-rw-r--    1 amit     amit         2374 Dec  3 10:50 xyz.java.save
  [amit@onyx handouts]:
  

• Hard links cannot be made to directories. For this purpose, a symbolic link can be used. Symbolic links can be used for files as well. A symbolic link is created with the ln command with the -s option. A symbolic link acts as a shortcut or pointer to the original file. However, if the original file is removed, the symbolic link is left dangling. See example below.

  [amit@onyx handouts]: ln -s xyz.java  f1
  [amit@onyx handouts]: ls -l f1 xyz.java
  lrwxrwxrwx    1 amit     amit            8 Dec  3 10:57 f1 -> xyz.java
  -rw-rw-r--    1 amit     amit         2374 Dec  3 10:57 xyz.java
  [amit@onyx handouts]: rm xyz.java
  rm: remove regular file `xyz.java'? y
  [amit@onyx handouts]: ls -l f1 xyz.java
  ls: xyz.java: No such file or directory
  lrwxrwxrwx    1 amit     amit            8 Dec  3 10:57 f1 -> xyz.java
  [amit@onyx handouts]: cat f1
  cat: f1: No such file or directory
  [amit@onyx handouts]:
  

  Symbolic links are useful for pointing to other directories or files without having to copy them, which would end up in duplicates that waste space and have to be kept consistent.