how do you "hard link" a whole directory?

isaaclw · 05-26-2010, 05:49 AM

I would like to mirror a folder with hardlinks.
Then I can go through and change some of the files, while keeping most the same.

The script I have so far is this:

Code:

#!/bin/bash
old="jaunty"
new="lucid"
dir="/conf"
cd $dir
find . -type d -exec mkdir -p $dir/$new/{} \;
find . -type f -exec ln $dir/$old/{} $dir/$new/{} \;

The problem with this is since I make the folders again, this doesn't preserve their permissions.
Is there any way to do this better? I feel like rsync should have an option for this, but I can't find it...

AlucardZero · 05-26-2010, 06:29 AM

Are you aware that hard links point to the same file and that changing a hard linked file under one name will change it under all names that refer to it?

catkin · 05-26-2010, 06:38 AM

How about using chmod and chown with the --reference option, something like find . -type d -exec mkdir -p $dir/$new/{} \; -exec chmod --reference {} $dir/$new/{} \; -exec chown --reference {} $dir/$new/{} \;

vorbote · 05-26-2010, 06:52 AM

You cannot hardlink a directory, at least when using filesystems that use traditional POSIX semantics; I bet BtrFS will let you do it with a judicious use of subvolumes sometime in the future.

Now, you can create directory trees with hardlinked files easily if using GNU coreutils and rsync. Use "cp -Hlr <fromdir> <targetdir>" to create the initial copy and "rsync -aHP --delete <fromdir> <targetdir>" for keep the target directory clean of cruft from time to time, else just fuggit about the latter. :-)

isaaclw · 05-26-2010, 07:24 AM

Quote:

Originally Posted by vorbote

Now, you can create directory trees with hardlinked files easily if using GNU coreutils and rsync. Use "cp -Hlr <fromdir> <targetdir>" to create the initial copy and "rsync -aHP --delete <fromdir> <targetdir>" for keep the target directory clean of cruft from time to time, else just fuggit about the latter. :-)

Actually, I'm pretty sure that these commands only keep Hard Links if there are any.
They don't make any new Hard links...

But the "find" command did it.

vorbote · 05-27-2010, 06:39 PM

Quote:

Originally Posted by isaaclw

Actually, I'm pretty sure that these commands only keep Hard Links if there are any.
They don't make any new Hard links...

But the "find" command did it.

You are wrong on both counts. Try them first, critique second. :-)

Shadow_7 · 05-28-2010, 05:50 AM

lndir

Although probably not hard links. But a common tool when building sources so as to not step on the source.

isaaclw · 06-09-2010, 10:06 AM

Quote:

Originally Posted by vorbote

You are wrong on both counts. Try them first, critique second. :-)

Ok, I admit, I didn't try them first, but I'm still right:
From the man pages of rsync:

Code:

        -H, --hard-links            preserve hard links

From the man pages of cp:

Code:

       -H     follow command-line symbolic links in SOURCE

But most importantly, when running the commands it takes up disk space:

Code:

cp -H /var/cache/apt-cacher/packages/* _import/
rsync -Ha /var/cache/apt-cacher/packages/ _import/

So... I guess back to the find command.

vorbote · 06-10-2010, 06:32 AM

Once again you are jumping to conclusions without even trying it youself.

Well, if you want to live like if it were 1985 and to discard information on what a poorly written man page says instead of trying it yourself, be my guest. :-)

isaaclw · 06-11-2010, 06:07 AM

Quote:

Originally Posted by vorbote

Once again you are jumping to conclusions without even trying it youself.

Well, if you want to live like if it were 1985 and to discard information on what a poorly written man page says instead of trying it yourself, be my guest. :-)

I'm going to ignore you insulted me, and ignore the fact that 1) you didn't notice that at the end I tried it and 2) you're apparently not trying yourself.

Instead, since we're two perfectly reasonable people, I'm going to preform a test that you can try yourself.

1) df -h:

Code:

Filesystem            Size  Used Avail Use% Mounted on
/dev/sdd2             9.9G  8.2G  1.3G  87% /media/gamma

This is the drive I'm working in.

2) cd /media/gamma
du -h --max-depth=1

Code:

root@lari-slow:/media/gamma# du -h --max-depth=1
16K     ./lost+found
4.7G    ./music
1.5G    ./comics
1.8G    ./pictures
163M    ./videos
8.0G    .

It seeems that Comics is just bigger then the space to fill the drive. No matter, if it's hard links it shouldn't take up space at all:
As you say, this should hard link the whole folder:

Code:

root@lari-slow:/media/gamma# rsync -aH comics/ comics2/

an hour later it finishes. No errors
and the drive is full:

Code:

Filesystem            Size  Used Avail Use% Mounted on
/dev/sdd2             9.9G  9.7G     0 100% /media/gamma

Now, I'll admit that I'm surprised that this 1.5 GB turned into 1.3 GB... however I'm not convinced that any hardlinks were made.

I would expect an apology towards anyone else who would have (no doubt) explained their situation better then I did. However, since I did a terrible job of explaining myself, I'll take the blame.

pixellany · 06-11-2010, 07:21 AM

vorbote and isaaclw;

No more personal jabs---OK?

wallbunny · 04-06-2011, 11:25 AM

I just found this thread since I had a similar problem, and I figured I should post how I solved it.
My problem was that I wanted to keep file and folder structure intact in case i messed up when renaming all my music files and folders.

cd /mnt/
rsync -a Music/ OldMusicDir/ --link-dest=/mnt/Music/
$ find Music/|wc -l
47732
$ find OldMusicDir/|wc -l
47732
$ du -h -s OldMusicDir/
1003G OldMusicDir/
$ du -h -s Music/
1003G Music/
$ du -h -s Music/ OldMusicDir/
1003G Music/
15M OldMusicDir/

Enjoy!