Binary package “fl-cow” in ubuntu bionic

copy-on-write utility

 Fl-cow allows you to utilise hard links to save disk space by causing
 hard-linked files to be copied rather than overwritten as they are changed.
 This is useful for making changes to large source trees while keeping a copy
 of the original tree to generate patches from. Also, if you are using the
 Arch revision control system with working copies hard-linked to a revision
 library, using fl-cow can prevent revision library corruption.
 Fl-cow is an LD_PRELOAD hack, not a kernel patch.