Now, because of what you said, I may instead try to get a similar result using ‘mount –bind’.

I’m trying to get the ‘/doc’ from ‘usr/share/doc’ off of a small SSD and onto a separate ‘/doc’ on a MMC in the memory slot of the same netbook. As well, I think the above command should also be insensitive to the SSD being ext4 and the MMC being formatted in ext3.

ln: creating hard link `hard' => `/disk2/somefile': Invalid cross-device link

Also, you can not format /dev/sdd1 as ext3 or ext4 at the same time or mount same device as ext3 or ext4 as same time as you need to format the file system. In short, hard link is not allowed between cross devices (it does not matter if devices are formatted as ext3 or ext4).

Another drawback of hard links is that they have to be located within the same file system, and most large systems today consist of multiple file systems.

Does mean, for example, you cannot make a hard link between and ext3 and ext4 file system, or does it mean you cannot link between file systems on two separate volumes?

I know this is two years old, but maybe some is watching? I have seen the above quote in a number of sources, but this one is the only one where there’s a chance to ask.

ln -fs file_location link_file_location
where
fs is forcefully and source respectively