> what is the recommended way of stopping a background
> job?
Err, in foreground, the ^C key if the best one. In background, first pause the
mirror as described later, and then use "kill <pid>" (not kill -9) to let
httrack know that you want to exit. Then, erase the hts-paused.lock file.

> Also is there a file whose existence will indicate
> whether a job is still running?  

hts-in_progress.lock