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What is a holey file?

Posted on 1997-10-12
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Last Modified: 2011-09-20
What is it? Why do they exist? Why I can't handle them as other files?
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Question by:jlms
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by:EricKaplan
ID: 2007394
"holey" file ? are you sure you got that right ?

-Eric.
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by:jlms
ID: 2007395
I think so...
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by:EricKaplan
ID: 2007396
Where did you get that info ? what OS ? ....
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rembo earned 50 total points
ID: 2007397


When you talk about holey files, I'm assuming
that you're talking about files which were
creating with empty checks via lseek.  

These are stored in the filesystem using
only header info, not real disk blocks.  However,
if you try to put this on to a tape, especially
with dd or something like that, it will try to
write the actual blocks.  

For example, you could lseek forward 2GB in a file
and then write 1 character.  Your file size is then
huge, but it actually only takes up one disk block
(this is in UFS, not any old SVR4 system).  However,
older filesystems can figure this out.

Anyway, the deal is you need to be careful with things
that might try to map these headers to real data.

So, the deal is, try not to create holey files :)
but if you do, just know what you're doing with
them and how you move them.  Try to use tar and
modern, ufs or vxfs filesystems.  

If there's a specific application you're wondering
about, let me know.  I'd be happy to help.

-Tony


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Author Comment

by:jlms
ID: 2007398
I think I understand, and no, I don't have any application in particular in mind.

One last thing, how can I recognize one of this files?
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Author Comment

by:jlms
ID: 2007399
I think I understand, and no, I don't have any application in particular in mind.

One last thing, how can I recognize one of this files?
0

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