Difference between a Hard Link and Soft (Symbolic) Link-布布扣-bubuko.com

Within the Unix/Linux file system, linking lets you create file shortcuts to link one or more files. Linux provides two different linking methods (hard and soft links) which will further be explained in this tutorial.

Introduction to Inodes:

To better understand how linking works, it may be easier to first understand the concept of inodes. Each file contains an index number called an inode. An inode (typically represented by a numerical value) is a data structure comprised of metadata information about the associated file. Linking utilizes inodes by pointing a file towards a specific inode value.

To view a file’s inode number, issue the command ls –i within the command prompt:

[Dillon@localhost Tutorial]$ ls -i
929447 example_file_1.txt
929448 example_file_2.txt
929449 example_file_3.txt

Creating a Hard Link:

A hard link essentially creates a mirror copy of the original linked file. Each hard linked file is assigned the same inode value as the original, therefore they both reference the same physical file location. Any changes to the data in either file is reflected in the other.

Hard links are beneficial as they are more flexible and remain linked even if the original or linked files are moved throughout the file system, although hard links are unable to cross different file systems. Lastly, hard links can only be assigned to files and not directories as to avoid recursive loops.

In the following example, the original file and hard linked file point to the same inode value of “101”.

To configure a hard link, issue the following command ln [original filename] [link name]

[Dillon@localhost Tutorial]$ ln original_file new_hardlink_file

[Dillon@localhost Tutorial]$ ls –l

-rw-rw-r--. 2 Dillon Dillon 28 Dec 28 14:28 new_hardlink_file
-rw-rw-r--. 2 Dillon Dillon 28 Dec 28 14:28 original_file

Creating a Soft Link (also known as Symbolic Link):

A soft link is similar to the file shortcut feature which is used in Windows Operating systems. Each soft linked file contains a separate inode value that points to the original file. As similar to hard links, any changes to the data in either file is reflected in the other.

Soft links are beneficial as they can be linked across different file systems, although if the original file is deleted or moved, the soft linked file will not work correctly (called hanging link).

In the following example, the softlink points to the location of the original file. Notice that both files contain different inode values.

To configure a soft link, issue the following command ln -s [original filename] [link name]

[Dillon@localhost Tutorial]$ ln -s original_file new_softlink_file

[Dillon@localhost Tutorial]$ ls -l

lrwxrwxrwx. 1 Dillon Dillon 28 Dec 28 14:32 new_softlink_file -> original_file
-rw-rw-r--. 1 Dillon Dillon 28 Dec 28 14:32 original_file

How to fix a hanging link:

To fix a hanging link, you must first determine the original file that the soft link pointed to. Issue the command ls -l command to verify this file – the broken link will typically be indicated by red colored text. In this example, the file “original_file” has been moved which resulted in the associated soft link to become broken.

[Dillon@localhost Tutorial]$ ls -l

lrwxrwxrwx. 1 Dillon Dillon 13 Dec 28 14:32 new_softlink_file - original_file

Next, you must determine where the new file is located. Issue the command find -name "filename" to locate the desired file:

[Dillon@localhost Tutorial]$ find -name "original_file"
Folder 1/original_file

Lastly, remove the current soft link by issuing the unlink [link name] command and re-configure the new soft link location with the following commands – notice when you issue the unlink command, the soft link file disappears:

[Dillon@localhost Tutorial]$ unlink new_softlink_file

[Dillon@localhost Tutorial]$ ls -l
            
[Dillon@localhost Tutorial]$ ln -s Folder_1/original_file new_softlink_file

[Dillon@localhost Tutorial]$ ls -l
lrwxrwxrwx. 1 Dillon Dillon 25 Dec 28 15:07 new_softlink_file -> Folder_1/original_file

Summary:

Hard Links:

Issue the ln [original filename] [link name] command to create a hard link
Original File and Hard Linked file contain the same inode value
Creates a mirror copy of the file
Any changes to either original file or hard linked file are reflected in the other file
Benefit – more flexible and remain linked if either the original or hard linked file is moved
Negative – unable to cross different file systems

Soft Links:

Issue the ln -s [original filename] [link name] command to create a soft link
Similar to shortcut feature in Windows Operating system
Original File and Hard Linked file contain different inode values
Each soft link file points to the original file’s inode
Any changes to either original file or soft linked file are reflected in the other file
Benefit – soft linked file can cross different file systems
Negative – if original file is deleted or moved, the soft link is broken (hanging link)

Difference between a Hard Link and Soft (Symbolic) Link

原文：http://www.cnblogs.com/kex1n/p/5142947.html