What is the difference between a symbolic link and a hard link?

Question

Recently I was asked this during a job interview. I was honest and said I knew how a symbolic link behaves and how to create one, but do not understand the use of a hard link and how it differs from a symbolic one.

Answer 1

Let's try to answer this question through technical description, and through example at the command line.

Hard Link: a "file handle", or name, that points to the same underlying file system i-node structure and data blocks. NOTE: because of this, hard links cannot span different file-systems.

Symbolic or Soft Link: is a special file-type that is basically a path-pointer, or "short-cut" in a Windows OS sense. NOTE: and so, Symbolic links can point to a file/directory in some other file system.

Also note, removing a hard-link leaves us with one less handle to the same underlying data/file.

Removing a symbolic link leaves us with one less path-pointer to an actual file or directory.

Removing the underlying file/directory renders and symbolic link that might have been pointing to it useless / undefined.

See the following sequence of commands and their output that hereby support what we said above.

$ touch file1 ## create a new file called file1 (empty)

$ ls -l file1

-rw-r--r-- 1 lji None 0 Apr 25 07:58 file1

$ ln file1 file2 ## create a hard link to file1

$ ln file1 file3 ## create another hard link to file1

$ ls -li file? ## notice the link count for these 3 "file handles" is 3 - and they share the same i-node number

10696049116135973 -rw-r--r-- 3 lji None 0 Apr 25 07:58 file1

10696049116135973 -rw-r--r-- 3 lji None 0 Apr 25 07:58 file2

10696049116135973 -rw-r--r-- 3 lji None 0 Apr 25 07:58 file3

$ ln -s file1 slink ## create a soft or sym-link to file1

$ ls -l slink ## show the path-pointer

lrwxrwxrwx 1 lji None 5 Apr 25 08:00 slink -> file1

$ rm file3 # remove one of the hard links

$ ls -l file? ## notice the link count now went to 2

-rw-r--r-- 2 lji None 0 Apr 25 07:58 file1

-rw-r--r-- 2 lji None 0 Apr 25 07:58 file2

$ rm file1 file2 # remove all handles to the original file we created

$ cat slink # now try using the sym-link - points to a non-existent file

cat: slink: No such file or directory

$ ls -l slink # but the link still exists

lrwxrwxrwx 1 lji None 5 Apr 25 08:00 slink -> file1

$ rm slink # so we may as well remove it ....

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