Find all hard links to a.txt in current directory:

find -xdev -samefile a.txt

Display the inode number of a.txt:

ls -i a.txt

Find all files (mutual hard links) with the same inode number 2000 in current directory:

find -xdev -inum 2000

-xdev means not descending directories on other filesystems. Omit it if you’re sure the operation is performed on a single filesystem.

Links: