Your /tmp is on a separate file system than /bin. _Hard_ links point to the same inode, therefore both parts of your link must be on the same file system (as op

Your /tmp is on a separate file system than /bin. _Hard_ links point to the same inode, therefore both parts of your link must be on the same file system (as opposed to a soft link, which is a separate inode saying "hey buddy, go over there"). It might work in something like /var/tmp, assuming that's not a soft link to /tmp like some systems do, or a separate file system.