How to find all hard links to a given file?
-samefile name
File refers to the same inode as name. When -L is in effect, this can include symbolic links.
hard-link
Hard-link creation – Permissions?
Which permissions affect hard-link creation? Does file ownership itself matters?
One file wants to belong to two users. How? Hard linking fails
Two setuid programs, /usr/bin/bar and /usr/bin/baz, share a single configuration file foo. The configuration file’s mode is 0640, for it holds sensitive information. The one program runs as bar:bar (that is, as user bar, group bar); the other as baz:baz. Changing users is not an option, and even changing groups would not be preferable.
Dereferencing hard links
In the manual page of tar command, an option for following hard links is listed.