Looking up reverse DNS to determine the hostname of an IP address thatyou are talking to is one of those almost simple things that softwarekeeps getting wrong .So here is how you do it, in two variants.

First, if you use DNS and have an (almost) empty /etc/hosts or justdon't care about looking up something in it, is the simple version:

• gethostbyaddr() the IP address. If it fails, you are done. Otherwiseyou have the claimed hostname .

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Once upon a time, I was at home and really needed to see somethingthat was displayed on my screen at work. This being Unix, there was noconvenient remote desktop add-on that would have let me mirror my workdisplay to home, but this being Unix, there are ways around that.

(Also, I was connecting over a slow dialup PPP connection , so a live remote desktop thing would havebeen difficult anyways.)

My first attempt was simple; ssh in to the work machine and do

I get it every so often: a new system that consumes my attention, mythoughts, and my interest. I find myself thinking about it all the timeand then working on it all the time; it doesn't matter that I'm not atwork, I want to work on it anyways so I do. And I'm impatient to seewhat I've built go into production, to actually get used, to give me feedback .

The current new system enthusiasm is for our new mail

A while back, I thought that a comment spammer had broken my simplescheme to prevent people from fetching the 'addcomments' page once and then using their zombie farm to submit spam, soI decided to switch to a more secure system for this. Since the weaknessin my scheme was spammers being able to replace my hidden informationabout the IP address that originally fetched the 'add comments' pagewith their own, the obvious fix was to sign the IP address using HMAC .

(It turned out that the