Arch Linux

patrickthebold

Member

Registered: 2008-12-15

Posts: 55

Quick Question on Hardlinks

If a file has two hard links and I edit it, should there still be two links to it? 

For example, when I do do the following "a" and "b" have the same inode:

sh-3.2$ echo foo > a
sh-3.2$ ln a b
sh-3.2$ echo bar >> b
sh-3.2$ ls -i
14049345 a  14049345 b

However if I edit a file with gnumeric I get different inodes:

sh-3.2$ gnumeric
Writing file:///a.gnumeric
sh-3.2$ ln a.gnumeric b.gnumeric
sh-3.2$ gnumeric b.gnumeric 
Reading file:///b.gnumeric
Writing file:///b.gnumeric
sh-3.2$ ls -i
14049346 a.gnumeric   14049347 b.gnumeric

Would this be considered a bug in gnumeric?  Should I not expect the two files to stay linked?  I'm not really sure how to use hard links with the two different behaviors.

fsckd

Forum Fellow

Registered: 2009-06-15

Posts: 4,173

Re: Quick Question on Hardlinks

No, apparently this is the recommended way of doing things.

Edit: You would expect Gnumeric to edit the file in place. What I think it is doing is replacing the entire contents of the file on write. I'm not sufficiently familiar with Gnumeric to explain why they chose this way. I can tell you this is the reason why the inodes are different.

Last edited by fsckd (2010-08-09 16:24:45)

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Trent

Member

From: Baltimore, MD (US)

Registered: 2009-04-16

Posts: 990

Re: Quick Question on Hardlinks

In a nutshell:  There is not likely to be enough space to edit the file in-place without lots of fragmentation, so most editors and userspace programs save modified copies rather than making in-place edits.

On the other hand, when you edit a file with Emacs or by using the -i flag to Perl or sed or any of a number of other command line apps, the original file is renamed without copying.

% ls -i text 
132109 text
% sed -i~ -e 's/e//' text
% ls -i text*            
132108 text  132109 text~

In this example, the original file was renamed and the modified copy was saved with the original name to a different inode.

Proofrific

Member

Registered: 2008-01-05

Posts: 215

Re: Quick Question on Hardlinks

% ls -i text 
132109 text
% sed -i~ -e 's/e//' text
% ls -i text*            
132108 text  132109 text~

In this example, the original file was renamed and the modified copy was saved with the original name to a different inode.

Nice example and explanation.