IPv6 has a neat feature called Duplicate Address Detection (DAD). When you add an IPv6 address to an interface, it checks to be sure that nobody else is already using that address. That's a Good Thing®. But if you're using IPv6 addresses for anycast and two (or more) devices are on the same subnet it can cause problems. The solution is to not put your anycasted addresses on the shared interface (e.g. eth0); rather, put them on the loopback interface.

Last week I dove in and wrote my first Android app. I've been waiting for a good reason to give it a try and one finally fell into my lap. I'm a volunteer member of a search and rescue team. We use management software from Radishworks.com named Mission Manager. They released an API the other day so I took up the challenge.

Today is the great SOPA/PIPA blackout. These are two proposed bills in Congress which would create a censorship regime for the Internet, much like China, Iran, and Syria have. And we know how great those governments are, so why wouldn't we follow in their footsteps? Wikipedia and Google are the most notable, but thousands of other sites went offline in protest. We at zmonkey.org fully support these actions.

South Korea is reportedly preparing to block TCP port 25 and force all mail traffic through "official mail servers", whatever that means. The BBC article isn't much on technical details. I'm still on the fence about blocking port 25. Fundamentally, I'm opposed to blocking ports outright. If somebody is shown to abuse a service, I'm fine with restrictions. I'm not excited about the prospect of requiring all mail to go through a central server, whether it's mine or someone else's.

Say you wanted to create a RAID1 device but didn't have all your devices ready. Here is how you could create a degraded RAID1 array and then add the second device at a later time. For these examples /dev/sda1 is the first device which will become our RAID and /dev/sdb1 will be added later.

First step is easy, create the RAID array. Our array will be /dev/md0. The "-n 1" option tells it that just a single device will be used and "-f" is required to use such a non-standard option.

$ mdadm --create /dev/md0 -l raid1 -f -n 1 /dev/sda1