Q: Single robots.txt file for all subdomains I have a site (example.com) and have my robots.txt set up in the root directory. I have also multiple subdomains (foo.example.com, bar.example.com, and more to come in the future) whose robots.txt will all be identical as that of example.com. I know that I can place a file at the root of each subdomain but I'm wondering if it's possible to redirect the crawlers searching for robots.txt on any subdomain to example.com/robots.txt?

A: Sending a redirect header for your robots.txt file is not advised, nor is it officially supported.
Google's documentation specifically states:

Handling of robots.txt redirects to disallowed URLs is undefined and discouraged. 

But the documentation does say redirect "will be generally followed". If you add your subdomains into Google Webmaster Tools and go to "Crawl > Blocked URLs" you can test your subdomain robots.txts that are 301 redirecting. It should come back as positively working.
However, with that said, I would strongly suggest that you just symlink the files into place and that each robots.txt file responds with a 200 OK at the appropriate URLs. This is much more inline with the original robots.txt specification, as well as, Google's documentation, and who knows exactly how bing / yahoo will handle it over time. 
