Re: [gentoo-user] Cloning a directory hierarchy, but not the content

[Etaoin Shrdlu]

On Sat, 29 Jan 2011 17:45:30 +0100 Alex Schuster <wonko@×××××××××.org>
wrote:

> Ah, now I get it. There's a -c missing after the sh command.

Right, thans for spotting it.


> > I should have added that, to do it safely, the target should reside
> > higher than the source in the hierarchy, or it should be on a different
> > filesystem and in that case -xdev should be specified to find
> > (otherwise an recursive loop would result).
>
> Right, but not important in my case. I want to mount my backup drive to
> /mnt, cd /mnt, and duplicate all stuff soemwhere else, without taking up
> much space. Then I can remove the backup drive and I only have to mount
> it again when I need a file's content, but not for finding out which
> files there are and how much space they take. Well, the space already is
> in the file created by du -m, but I'd like to directly navigate around.

Oh, I see now: you want the files to *look like* the real ones (eg when
doing ls -l etc.), but be sparse so they don't take up space?
 
> Sparse files would be nice because then I do not only have the same
> logical structure, the files also appear to have the same size as the
> originals, instead of having a size of 0. I could navigate and explore
> the directory structure with mc, and with du --apparent-size I could find
> out how much space a subdirectory takes. Again, my du -m file already has
> this information, but while navigating in the directory tree, being able
> to use du would be nice.

Ok, one way to create a sparse file of, say, 1 megabyte is using dd:

# dd if=/dev/null of=sparsefile bs=1 seek=1M
0+0 records in
0+0 records out
0 bytes (0 B) copied, 2.5419e-05 s, 0.0 kB/s
# ls -l sparsefile 
-rw-r--r-- 1 root root 1048576 Jan 29 11:57 sparsefile
# du -B1 sparsefile
0	sparsefile

Another way, already suggested, is by using truncate, eg

# truncate -s 1M sparsefile