[NTLUG:Discuss] "Undo" hard links?

[Cornelius Keck]

Yes... brute force might do the trick. Make sure you have enough disk 
space. Given this scenario:

pi at pi1b00:~/tmp $ ls -ls
total 12
4 -rwxr-xr-x 1 pi pi  139 Nov 10 18:12 breakLinks.sh
4 drwxr-xr-x 2 pi pi 4096 Nov 10 18:11 D1
4 drwxr-xr-x 2 pi pi 4096 Nov 10 18:11 D2
pi at pi1b00:~/tmp $ ls -ls D*
D1:
total 0
0 -rw-r--r-- 2 pi pi 0 Nov 10 18:11 f1

D2:
total 0
0 -rw-r--r-- 2 pi pi 0 Nov 10 18:11 f2
pi at pi1b00:~/tmp $

of two subdirectories, D1 containing one file, D2 a hard link to that 
same file (link count of f2 is the same as the one of f1, and larger 
than 1 (one)), run this script:

pi at pi1b00:~/tmp $ cat breakLinks.sh
#!/bin/sh
find . -type f -links +1 -print | while read line
do
     cp "$line" "$line.tmp"
     rm -f "$line"
     mv "$line.tmp" "$line"
done
pi at pi1b00:~/tmp $

This looks for files (type f) in the current directory, with more than 
one reference, i.e. inode reference count larger than 1 (one) (-links 
+1), then, for each found, copies it aside, removes the original 
(reducing the inode's link count), moving the temporary copy back into 
place. The quotes around $line are there to keep the script from acting 
up when running into file names containing spaces.

Running that results in:

pi at pi1b00:~/tmp $ ./breakLinks.sh
pi at pi1b00:~/tmp $ ls -ls D*
D1:
total 0
0 -rw-r--r-- 1 pi pi 0 Nov 10 18:23 f1

D2:
total 0
0 -rw-r--r-- 1 pi pi 0 Nov 10 18:23 f2
pi at pi1b00:~/tmp $

Same as before, but the link count is 1 (one).

If the files' timestamp is important, use "cp -p".

Sure, one could do this in a one-liner using find's -exec option, but 
that's makes for a less readable explanation.

On a personal note, Google Drive is hosted on somebody else's computer, 
so there is always the chance that somebody else might get to your data, 
or that Google turns off access on short notice, or changes its terms 
and conditions. While it is a convenient feature, from a privacy and 
security perspective, a local backup is preferable. Besides, external 
disk drives are fairly cheap, Black Friday is coming up, and chances are 
that your uplink is not as fast as a USB3 wire.


Lance Simmons wrote:
> I recently created a lot of hard links, thereby reducing the disk space
> used by my Documents directory by a chunk. I was feeling pretty good about
> this, but then discovered that Google Drive does not acknowledge hard
> links. Every time the folder is synchronized (via a cron job), a few
> hundred bogus "conflicts" are declared and  then resolved. Then, the next
> time the folder is synchronized, the same "conflicts" are found and
> resolved again.
> 
> I love the idea of hard links, but now I want to return to having separate
> files. Is there an easy way to (1) delete hard links, then (2) copy the
> files (inodes), giving them the filesystem names of the original hard
> links?
> 
> I should switch away from Google Drive; maybe this annoyance will motivate
> me.
> 
> Lance
>