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HARDLINKS AND SYMLINKS


Today we will test your virtual imagination capabilities !

The main difference between hardlinks and symlinks ( symbolic or softlinks ) are:
1.) You cannot make a hardlink to a directory.
2.) If you remove the original file of a hardlink the link will still show you the content of the file.
3.) A symlink can link a directory
4.) The symlink is useless as you remove the original file.

All this might seem hard to grasp, but let´s explain:


Hardlinks

A little experiment to show the case.

CODE
$ mkdir Test

( Making a new directory for our test )

CODE
$ cd Test

( Move in the directory )

CODE
$ vi fileA

( Make a file called fileA )

"i"
Type in some funny lines of text
< Esc >
ZZ ( save the file )

So, we made a ¨fileA¨ in a new directory called ¨Test¨ in your /home.

CODE
$ ln fileA fileB

( Making a hardlink )

CODE
$ ls -il fileA fileB

( The ¨i¨ argument will show the inode on the HD )
This is what you get:

QUOTE (Text @ Screen)
1482256 -rw-r--r--       2 bruno  bruno         21 May  5 15:55 fileA
1482256 -rw-r--r--       2 bruno  bruno         21 May  5 15:55 fileB


Here you can see that both fileA and fileB have the same inode number ( 1482256 ), also both files have the same file permissions and the same size, because that ´size´ is on the same inode it does not consume any extra space on your HD !

Now if we would remove the original ¨fileA¨

CODE
$ rm fileA

and have a look at the content of the ¨link¨ fileB

CODE
$ cat fileB

you will still be able to read the funny line of text you typed. ( MAGIC ! )




Symlinks

Staying in the same test directory as above we make a symlink:

CODE
$ ln -s fileB fileC
$ ls -il fileB fileC

This is what you´ll get:

QUOTE (Text @ Screen)
1482256 -rw-r--r--           1 bruno  bruno        21 May  5 15:55 fileB
1482226 lrwxrwxrwx       1 bruno  bruno          5 May  5 16:22 fileC -> fileB


You´ll notice the inodes are different and the link got a ¨l¨ before the rwxrwxrwx . The link has different permissions than the original file because it is just a symbolic link, its real content is just a string pointing to the original file. The size of the symlink ( 5 ) is the size of it´s string. ( The "-> fileB" at the end shows you where the link points to )

CODE
$ cat fileB

and

CODE
$ cat fileC

Will show the same funny text.

Now if we remove the original file:

CODE
$ rm fileB

and check the Test directory

CODE
$ ls

you will see the link fileC is still there, but if we do

CODE
$ cat fileC

it will tel you that there is no such file or directory !! Though

CODE
$ ls -il fileC

will still give you:

QUOTE (Text @ Screen)
1482226 lrwxrwxrwx      1 bruno  bruno      5 May  5 16:22 fileC -> fileB

But the link is obsolete ! ( hope you´re still with me )

O.K. The test is over, you can delete the Test directory

CODE
$ cd ..
$ rm -rf  Test

( ¨r¨ stands for recursive ¨f¨ is force )


WARNING: "rm -rf" is very powerfull, if ever someone wants to play a trick on you and tells you to do "rm -rf /" as root, you might loose all your files and directories on your / partition !!!

Not dizzy yet ? Wait till next week when we come to the real stuff !


Bruno


-- May 5 2003 ( Revised Dec 10 2005 ) --


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