Does this robot.txt file: User-agent: * Allow: /. Allow: / Allow all crawlers to crawl my site? or does it stop them!
User-agent: * Disallow: Disallow: /cgi-bin/ you can simply use this or you can go to google webmasters tools and generate your own robots.txt Hooooray !
If you want to allow ALL crawlers to crawl your entire site then you don't even need a robots.txt unless you want to include a sitemap.xml for discovery by the bots. If you do insist on having one even though you want all crawlers to crawl your entire site then as maineexista said you only need:
You really only need one like I said if 1) there are certain pages you DO NOT want indexed OR 2) if you want to specify a sitemap.xml in your robots.txt so bots can auto-discover it. Otherwise, having one serves no purpose. The bots that you DO NOT want crawling your site likely ignore it anyway.
Not entirely true - raise your hand if you like seeing your site's server logs cluttered with 404 errors due to a missing robots.txt file every time it gets requested. At the very least, having one will prevent those pointless errors and clean up the log fie. Oh, and as far as bots are concerned, you mean like Yahoo! Slurp?
I know, but one of my friends happens to manage a very large online gaming community site for a niche tabletop game publisher, and Yahoo! was constantly hammering his server last year (he has his own dedicated server). He eventually traced it down to Yahoo! Slurp, then added a Disallow directive which the bot ignored. So he got ticked off, said "screw it" and banned the entire IP block. (If you don't believe me, you can ask him here on Digital Point. His username is deathshadow.)