Symlinks & Hardlinks

Files are arranged in directories (or folders if you prefer that term), and each file can be reached through a series of directories and subdirectories from the root - correct? Yes ... BUT ... there are some times that the same file can be reached through several names, and on Unix and Linux systems this is known as a "link". There are two ways a link can be set up.

Hard Link

A Hard Link is where a file has two names which are both on an equal weighting, and both of the file names in the "inode table" point directly to the blocks on the disc that contain the data. See diagram to the left. 
You set up a hard link with an ln command without options - if the file ab.txt already exists and you want to give an additional name (hard link) to it, you'll write

#ln ab.txt cd.txt

and then both names will have equal ranking. The only way you'll know that there's a link there is by doing a long listing and you'll see a link count of 2 rather than 1, and if you need to find out what's linked to what, use the -i option to ls.

Symbolic Link

A Symbolic Link is where a file has one main name, but there's an extra entry in the file name table that refers any accesses back to the main name. This is slighly slower at runtime that a hard link, but it's more flexible and much more often used in day to day admin work. Symbolic links are set up using the ln command with the -s option - so for example

#ln -s ab.txt cd.txt

will set up a new name cd.txt that points to the (existing) file ab.txt. If you do a log listing (ls -l) of a directory that contains a symbolic link, you'll be told that it's a symbolic link with an "l" in the first column, and you'll be told where the file links to in the file name column. Very easy to spot!
Soft Links(Symbolic Links) :
1. Links have different inode numbers.
2. ls -l command shows all links with second column value 1 and the link points to original file.
3. Link has the path for original file and not the contents.
4. Removing soft link doesn't affect anything but removing original file the link becomes dangling link which points to nonexistant file.

In Softlink Inode is diff and the linked file will b a shortcut of first file

Hard Links :

1. All Links have same inode number.
2. ls -l command shows all the links with the link column(Second) shows No. of links.
3. Links have actual file contents
4. Removing any link just reduces the link count but doesn't affect other links.

In Hardlink Inode is same and both are independent Soft link can create directories but hard link can't. Hard links created within that particular file system but soft link cross that file system
Hard links canot cross partition.
A single inode number use to represent file in each file system. All hard links based upon inode number.
So linking across file system will lead into confusing references for UNIX or Linux. For example, consider following scenario

* File system: /home
* Directory: /home/alex
* Hard link: /home/alex/file2
* Original file: /home/alex/file1
Now you create a hard link as follows:
$ touch file1
$ ln file1 file2
$ ls -l
Output:
-rw-r--r-- 2 alex alex 0 2006-01-30 13:28 file1
-rw-r--r-- 2 alex alex 0 2006-01-30 13:28 file2

Now just see inode of both file1 and file2:

$ ls -i file1
782263
$ ls -i file2
782263

As you can see inode number is same for hard link file called file2 in inode

table under /home file system. Now if you try to create a hard link for /tmp file system it will lead to confusing references for UNIX or Linux file system.
Is that a link no. 782263 in the /home or /tmp file system? To avoid this problem UNIX or Linux does not allow creating hard links across file system boundaries.