I manage a server which has a sole purpose: serving DNS requests. We use PowerDNS, which has been great. It is a DNS server whose backend is SQL, making administration of large numbers of records very easy. It is also fast, easy to use, open source and did I mention it is free?

The server has been humming along for years now. The traffic graphs don’t show a lot of data moving through it because it only serves DNS requests (plus MySQL replication) in the form of tiny UDP packets.

Read on to follow my story of how I fixed this tricky problem. No kittens were harmed in the writing of this post.

It is very easy to create a random file using the linux command line. Much like the command to fill a file with all zeros, for example a 1 Meg file: dd if=/dev/zero of=zero.filename bs=1024 count=1000 You do the same using /dev/urandom: dd if=/dev/urandom of=random.filename bs=1024 count=1000 Resulting in a 1MB file: 1000+0 records in […]

We recently did some speed testing on a few of the servers on our network, and we were not receiving the speeds expected considering they were sitting on a physical 100mbps ethernet port. The servers were indeed on physical 100mbps connection, however wget (TCP/IP, HTTP Port 80) download tests showed only a max of about 1.5MB/sec (note the 8bit/byte conversion, so this translates to about 12mbits).

Did you ever have a situation where you needed to access a website that had an IP restriction in place? I recently had a situation where I needed to access the web via my university connection (due to IP restrictions placed on accessing databases of research papers). They do not have a VPN setup so […]

Have you ever come across a server that is doing a lot of traffic? Maybe you have logged in to see a process running at 100% CPU, so you know the culprit, but instead of kill -9ing it, wouldn’t it be great to see what exactly it is up to? Or even if you see […]

I recently received this error while mounting an iso image in a CentOS 5.3 install: [root@host ~]# mount -t iso9660 -o loop /mnt/glusterfs/ecp-spe-4867.iso /mnt/iso/ ioctl: LOOP_SET_FD: Invalid argument For more detail: [root@host ~]# mount -v -t iso9660 -o loop /mnt/glusterfs/ecp-spe-4867.iso /mnt/iso/ mount: going to use the loop device /dev/loop0 ioctl: LOOP_SET_FD: Invalid argument mount: failed […]

I recently came across a typo that existed in a bunch of html files on my web server. I thought it should be easy enough to change, but since it was in a number of files, editing it by hand would be time consuming. Fortunately, there is an easy, one liner command to replace the […]

If you wish to run a command which typically uses a lot of CPU (for example, running tar on a large file), then you probably don’t want to bog down your whole system with it. Linux systems provide the nice command to control your process priority at runtime, or renice to change the priority of […]

In case you were wondering, I just invented the phrase PVPN – Personal Virtual Private Network. I use Hamachi to connect my work, home and laptop PCs and I’ve found it invaluable over the past few years for a number of reasons. Music over VPN, Remote Desktop/VNC over VPN, and more. So now, I’d like […]

Adding swap space is pretty easy. This will add more, but slower ram; helping you when dealing with large files. In general, linux likes to have twice the amount of swap space as RAM. Since the N800 has 128M memory, I’m adding 256M. We’ll see how this perform in the long run. Before, no swap […]