cowdancer 0.86 (amd64 binary) in ubuntu bionic

 Tries to make copy-on-write semantics upon hard-link copied
 directory trees generated with 'cp -la'
 .
 'cow-shell' command invokes a shell session. Within that session,
 under the directory cow-shell was invoked,
 cowdancer will create a new file when existing i-nodes are opened for
 write.
 Useful for quick scratch workspace and experimentation.
 .
 For a useful Debian tool, try cowbuilder.