restrict domain/subdomain robots.txt

[Gatz]

Hello,
1. I use 2 domains pointed to the same content
domain1.com
domain2.com
The thing is, I don't want domain2.com to be indexed by any search engine. How I do that?

2. I'm using wildcard subdomains and I'd like to restrict some on them to be indexed.
3. I'm using joomla, if I want to restrict an entire category (domain.com/cat), it will work if I add on robots.txt "Disallow: /cat/" ?

Thanks