Etaoin Shrdlu writes: > On Sat, 29 Jan 2011 17:45:30 +0100 Alex Schuster <wo...@wonkology.org> > wrote:
>>> 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? Exactly. Sorry I did not make myself clearer. It's working now, and I like it :) I added some more features, like clipping files to a maximum size. So the clone can still be very small compared to the original, with small files being intact and usable. > 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 That's how I wanted to do it first, too. > Another way, already suggested, is by using truncate, eg > > # truncate -s 1M sparsefile I used this, because so I can modify a file that I created empty with cp --attributes-only. Keeping the attributes would have been a bit complicated. In case anyone else is interested, the script is here: http://www.wonkology.org/utils/clone0 wonko@weird ~ $ clone0 -h clone0 version 2011-01-29 Duplicate a file / directory hierarchy. Files are created as sparse files, not taking up real space. Usage: clone0 [-dhSv0] [-s size] src... dst Options: -d clone directory structure only, not files -h show this help -s size copy files up to size as the are, and clip larger files -S do not create sparse files -v show directories being created -vv show files being created -vvv debug output -0 clip files larger than size (option -s) to zero size Arguments: src... one or more directories to clone dst destination directory (will be created) Thanks for the input, guys! Wonko
