Sponsored Content
Operating Systems Solaris Difference between hard link and copy command Post 302378252 by jim mcnamara on Monday 7th of December 2009 10:35:59 AM
Old 12-07-2009
Here is an oversimplified analogy:

Think of a hard link as a pointer in the filesystem. Just like in C, it has to be dereferenced. But instead of what a pointer does: refer to a separate place in memory, with a hardlink we are referred to a place on the physical disk. The link acts as a proxy for the "real" filename.

The C pointer uses very little memory, but can reference a giant object in memory.

A hard link uses very little disks space but can reference a huge file.

How hard links are implemented is not by a universally defined object, but is up to the filesystem and the drivers to resolve. This is like C: a pointer can be a "big-endian" or a "little-endian" object in memory, and the compiler works out how to reference the object the pointer is "aimed" at. The filesystem + driver does the same. We do not worry about how to figure it out at all.

Links have consequences. One of them is that you do not ever want dangling links - links "aimed" at non-existent. It is possible to create a series: link -> link -> physical file. This is where it is easy to get in trouble. You can create circular links in some circumstances.

Copy duplicates a whole file. Link references a whole file.

Last edited by jim mcnamara; 12-07-2009 at 12:10 PM..
 

10 More Discussions You Might Find Interesting

1. UNIX for Advanced & Expert Users

Differences between hard link and soft link

Hi all! I'd like to know the differences between hard links and soft links. I've already read the ln manpage, but i'm not quite sure of what i understood. Does a hard link sort of copy the file to a new name, give it the same inode number and same rights? What exactly should I do to do this:... (3 Replies)
Discussion started by: penguin-friend
3 Replies

2. UNIX for Dummies Questions & Answers

Why use a hard link

Someone asked me a question today about the difference between a hard link and a soft link. That got me thinking and maybe someone can answer. Why would I ever use a hard link if I can use a soft link instead? (2 Replies)
Discussion started by: dangral
2 Replies

3. UNIX for Dummies Questions & Answers

Difference between hard link and soft link in unix

Hi All, Can any one please explain me what is the difference between hard link and soft link in UNIX. Thanks in advance Raja Chokalingam. (2 Replies)
Discussion started by: RAJACHOKALINGAM
2 Replies

4. UNIX for Dummies Questions & Answers

need some info about symbolic link and hard link

hello folks how y'all doin well i have some questions about symbolic link and hard link hope some one answer me i open terminal and join as root and i wrote ln -s blah blah then i wrote ls i see red file called blah blah but didn't understand what is this can some one explain and... (2 Replies)
Discussion started by: detective linux
2 Replies

5. UNIX for Advanced & Expert Users

Hard link

Hello, In unix, the normal user can't create a hardlink for a directory. why..? Is there any difference between creating a hard link for a file and directory? The super user can create a hard link for directories. Why we cannot create and super user can create.? Please, can anyone help... (1 Reply)
Discussion started by: nagalenoj
1 Replies

6. UNIX for Dummies Questions & Answers

Hard Link vs SOft Link????

Hi PLease let me know the usage of Hard Link vs Soft Link i.e what is the basic difference and what happens when one file is changed or deleted in both the cases??? thanks (3 Replies)
Discussion started by: skyineyes
3 Replies

7. UNIX for Dummies Questions & Answers

Difference between hard link and soft link

Hi Experts, Please help me out to find out difference between a hard link and a soft link. I am new in unix plz help me with some example commands ( for creating such links). Regards S.Kamakshi :) (2 Replies)
Discussion started by: kamakshi s
2 Replies

8. Shell Programming and Scripting

Find Hard Link

Goodmorning everybody. A question: How can i match if a file is an hard link or not? (6 Replies)
Discussion started by: Guccio
6 Replies

9. UNIX for Advanced & Expert Users

Hard Link Examples

Hello, Please move this if I chose the wrong forum category. This question pertains to Unix and Linux I believe. I google the difference between hard and symbolic/soft links and I understand the difference. What I am trying to find is a real example of a hard link being used in a Operating... (11 Replies)
Discussion started by: jaysunn
11 Replies

10. Solaris

difference between copy and mcopy command

Hi, Can anyone explain me the usage of mcopy command and also the difference between copy and mcopy. As per my understanding through both we can copy multiple files or DOS files . Any help on this will be really helpful. (3 Replies)
Discussion started by: rogerben
3 Replies
SYMLINKS(8)						      System Manager's Manual						       SYMLINKS(8)

NAME
symlinks - symbolic link maintenance utility SYNOPSIS
symlinks [ -cdrstv ] dirlist DESCRIPTION
symlinks is a useful utility for maintainers of FTP sites, CDROMs, and Linux software distributions. It scans directories for symbolic links and lists them on stdout, often revealing flaws in the filesystem tree. Each link is output with a classification of relative, absolute, dangling, messy, lengthy, or other_fs. relative links are those expressed as paths relative to the directory in which the links reside, usually independent of the mount point of the filesystem. absolute links are those given as an absolute path from the root directory as indicated by a leading slash (/). dangling links are those for which the target of the link does not currently exist. This commonly occurs for absolute links when a filesystem is mounted at other than its customary mount point (such as when the normal root filesystem is mounted at /mnt after booting from alternative media). messy links are links which contain unnecessary slashes or dots in the path. These are cleaned up as well when -c is specified. lengthy links are links which use "../" more than necessary in the path (eg. /bin/vi -> ../bin/vim) These are only detected when -s is specified, and are only cleaned up when -c is also specified. other_fs are those links whose target currently resides on a different filesystem from where symlinks was run (most useful with -r ). OPTIONS
-c convert absolute links (within the same filesystem) to relative links. This permits links to maintain their validity regardless of the mount point used for the filesystem -- a desirable setup in most cases. This option also causes any messy links to be cleaned up, and, if -s was also specified, then lengthy links are also shortened. Links affected by -c are prefixed with changed in the output. -d causes dangling links to be removed. -r recursively operate on subdirectories within the same filesystem. -s causes lengthy links to be detected. -t is used to test for what symlinks would do if -c were specified, but without really changing anything. -v show all symbolic links. By default, relative links are not shown unless -v is specified. BUGS
symlinks does not recurse or change links across filesystems. AUTHOR
symlinks has been written by Mark Lord <mlord@bnr.ca>, the developer and maintainer of the IDE Performance Package for linux. SEE ALSO
symlink(2) Version 1.2 November 1994 SYMLINKS(8)
All times are GMT -4. The time now is 03:49 PM.
Unix & Linux Forums Content Copyright 1993-2022. All Rights Reserved.
Privacy Policy