[X-Unix] Strange Files , .DS_Store, ._c.zip Etc...

[Alex]

On Apr 21, 2005, at 8:43 AM, Long, Jason wrote:

> Everytime I SSH Into my Mac from work, I see all of these .DS_Store
> files which I have no idea what they're for

Hidden (invisible) files in which Finder keeps folder metadata (icon  
position, etc.)

> I have a file that is like this  C.zip  and in the ssh window
> there's also a file like this ._c.zip what's up with that?

Macintosh files have a "forked" structure, i.e., data in a Mac file can  
be stored in two different forks, the data fork and the resource fork.  
You could visualise it as two files which share the same name. This  
structure is supported by the Mac file system, HFS+ (which, in fact,  
has the rudiments of support for an arbitrary number of forks).  
However, most other file systems do not support such a structure. When  
presented with a Mac file, a file system such as UFS or NTFS will  
simply accept the data fork and discard the resource fork. To get  
around this problem, Apple has created the Apple Double mechanism for  
interfacing with FSs without fork support. Apple Double splits a forked  
Mac file into two files, putting the data fork into a file with the  
original name, and the resource fork into another file with the same  
name prefixed by "._".

So what you see is the side-effect of accessing an HFS+ volume through  
AppleDouble from a file system which doesn't support forks. If you find  
that confusing, turn off the display of hidden and system files in  
WinSCP (ctrl-alt-H)

> Is it safe to delete these files

For files residing on non-HFS volumes, such as FAT32 or NTFS under  
Windows, yes. For files residing on an HFS+ volume (Mac), it depends.  
Many documents have no resource fork (or 0 length resource fork). Some  
documents contain in the resource fork non-essential data, such as the  
state of text documents or previews of JPEG images. Deleting this stuff  
won't make much of a difference. However, some applications and other  
resources store crucial data in the resource fork. (For instance, the  
vector data of Mac TrueType fonts is stored in the sfnt resource in the  
resource fork.) Deleting the ._ file in this case will destroy the  
original.

So the safe answer is: You may delete the ._ files which have been  
copied over on the Windows disks -- unless you ever plan to copy them  
back to a Mac disk. You shouldn't delete the ._ files on any Mac volume  
accessed under another operating system.

For more information on data/resource forks, read the respective  
chapters in Inside Mac: Toolbox Essentials, and Inside Mac: More  
Toolbox.

<http://developer.apple.com/documentation/mac/Toolbox/Toolbox 
-17.html#HEADING17-0>
<http://developer.apple.com/documentation/mac/MoreToolbox/MoreToolbox 
-11.html#HEADING11-0>

For more information on HFS+, read Apple Tech Note 1150

<http://developer.apple.com/technotes/tn/tn1150.html>


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