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rsync copied 0-byte source file
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nordic bro
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Joined: 25 Oct 2003
Posts: 582

PostPosted: Fri Sep 27, 2013 7:16 pm    Post subject: rsync copied 0-byte source file Reply with quote

I'm kind of new to rsync and this is the cmd I use:

rsync -axu --delete

there are a number of source partitions I backup to similarly-sized target partitions on a separate disc. I run "$rsync_cmd $source/ $target/" from a script and after lots of double-checking initially it seemed to have been working great for many months.

the other day in source /etc I came across 0-byte ntp.conf and have no idea how that happened. so I mounted the corresponding rsync target to copy the file back but found its npt.conf was also 0-byte.

that 0-byte file was the only one in target /etc, all the rest there looked ok so it seems my source ntp.conf got wiped out and when I did a subsequent rsync my good target copy got replaced.

so is there an rsync option I can add that would tell rsync to never replace something on target w/0-byte source file?

thanks.
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eccerr0r
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Joined: 01 Jul 2004
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PostPosted: Sat Sep 28, 2013 12:06 am    Post subject: Reply with quote

What if you deliberately zeroed out the file and needed an empty file, and needed a full restore - you'd also end up with a broken system.

Maybe the best way is to RCS all of these files... but the original way to deal with this is to have rotating and incremental backups or a version controlled filesystem.

I suppose the least software way to do this is to use

find /sourcedir -size 0 -type f > /tmp/newzerosized.txt
find /destdir -size 0 -type f > /tmp/oldzerosized.txt
[insert magic here to remove all old zerosized files from newzerosized file list]

to find empty files, and tell rsync --exclude-from /tmp/skipzerosized.txt to skip them. Or you could do away with checking old ones and just let it skip them too even if they've never been copied.

Not a very clean solution either way...

(I was experimenting with a deduplication filesystem as backup, but lessfs is crap for large number of small file backups.)
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Hu
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Joined: 06 Mar 2007
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PostPosted: Sat Sep 28, 2013 3:03 pm    Post subject: Reply with quote

According to man rsync, you can use --min-size to implement this. However, as eccerr0r says, this may not be the right choice in some situations, so think carefully before deploying it across a large area.
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