Why are hard links are not updated when modified with an editor

Question

I am using Mac OS X, but the command line. I want to make a link from my .profile file, to another file on my system so that updating one updates the other and vice versa.

This article makes me think that a hard link is what I need. The command I have been using is:

ln .profile ~/Newpath/.profile

This kind of works, in that a file is created at Newpath, however, updating one file does not automatically update the other nor vice versa.

I have tried ln with simple files on my desktop, and the links do indeed update each other. I am wondering if anybody has experience with links not working with dot files or with files in their home directory on Mac for some reason.

Any idea what could be going on here?

score 15 · Answer 1 · answered Jun 14 '16 at 15:28

15

Beware that many editors write to a temporary file and rename finally to the target file.

This will cause your hard-linking to be lost.

answered Jun 14 '16 at 15:28

Raúl Salinas-Monteagudo

371

4

What do you do about this? This seems to be my case. – Michael Bruce Feb 02 '17 at 16:29

score 3 · Answer 2 · answered Sep 25 '15 at 06:04

3

Perhaps the directories where these files reside are on different filesystems / partitions? Hard links can only exist on a single partition.

if test x"$(stat -f'%d' .)" != x"$(stat -f'%d' ~/Newpath)"; then
  echo "Directories are on different partitions"
fi

answered Sep 25 '15 at 06:04

dubiousjim

2,698

3

If they were different filesystems, the ln command would have failed. – Stéphane Chazelas Jun 14 '16 at 15:35
Yes, @StéphaneChazelas is correct. – dubiousjim Jun 14 '16 at 17:35
This is not the case in the question, since it works for the first time but not after updates. – Raúl Salinas-Monteagudo Jul 14 '16 at 15:29

score 1 · Answer 3 · answered Sep 25 '15 at 05:42

1

I just tested it on my Mac, it worked perfectly well.
Updating either of them, the other one would be updated too.

BTW, symbolic link should work as well as hard link.

answered Sep 25 '15 at 05:42

SparedWhisle

3,668

1

I am using hard links because I wanted to use git with these files. I added clarification to my question because the linking does indeed work on simple text files, on my desktop for example but not with these dot files in my home directory. – Startec Sep 25 '15 at 05:45
7

I think git will break hard links every time you checkout a new copy of the file. EDIT: Yes, I just verified it will, even if the hard links are in a single repo. – dubiousjim Sep 25 '15 at 07:07
This is actually the real culprit I believe. – Startec Aug 05 '16 at 07:53
Git should work reasonably well with symbolic links, though. Even if the underlying filesystem doesn't support them (e.g., FAT32), git will mimic them via text files (but you won't be able to use them). – leden Sep 28 '16 at 01:18

score 0 · Answer 4 · answered Aug 01 '17 at 18:01

0

I also faced the same issue when writing with TextEdit. So then, I tried with cat command and it worked perfectly.

answered Aug 01 '17 at 18:01

kaushik3993

1

You tried *what* with a cat command? – G-Man Says 'Reinstate Monica' Aug 01 '17 at 18:26
I gave input to the file using cat command instead of writing through some editor. – kaushik3993 Aug 02 '17 at 05:28

score 0 · Accepted Answer · answered Oct 21 '19 at 06:09

0

dubiousjim's comment pointed out my issue:

I think git will break hard links every time you checkout a new copy of the file. EDIT: Yes, I just verified it will, even if the hard links are in a single repo

answered Oct 21 '19 at 06:09

Startec

1,879

Why are hard links are not updated when modified with an editor

5 Answers5