Symlink a directory and automatically sync its content

Question

Suppose I have a folder foo with the two content:

data1.txt
cfg.txt

Now I create a new symlink called fo2 which points to directory foo:

cp -s -R /home/user123/foo /home/user123/fo2

It's working okay. But then, I try to made new files in foo folder, say data2.txt. When I opened fo2 folder, it only contains a symlink to data1.txt and cfg.txt data2.txt doesn't exist.

How to make the content of fo2 folder automatically synced with with foo so data2.txt automatically appears in fo2?

ln -s is not an option because I want the content of cfg.txt in foo and fo2 folder to be different. If I use copy -s -R, later I just come inside fo2 folder, delete cfg.txt symlink and recreate a real cfg.txt with different content.

Answer 1

If the locations are both on the same filesystem, you should use hard links. Otherwise, you'll have to setup some sort of synchronization, but that will be extremely inefficient in comparison.