I'd like to see if a hard disk is being actively used right now (a hddled-like indicator) and what particular files are being accessed. How can I achieve this in command line with SSH?
Assuming you wanted to run the command through ssh and not just ssh directly to the machine. The command from ssh will look some thing like this:
ssh <hostname> lsof <options>
If you need this to run as root from a script, slightly fancy use of sudo and ssh keys should get you no requirement for a password. But be careful slightly to fancy use of sudo and ssh keys can just up and give anybody root access to your box.