I really like linux and the various BSDs as a server platform, so I’m going to focus mainly on that.  I’ll still talk about virtualization, but not working with vmware everyday anymore has made me lose interest.  This blog is going back to my roots, web programming, unix administration, and solving obscure problems.  That’s what I do best.

If you need some work done on a server, or want to host a site with a provider that is exclusive and knowledgeable, drop me an email at michael [at] venturehosting.net and I can probably help you.  I am very selective about who I work for, but if I decide to work with you, I’m sure you’ll be pleased with the results.  If I decide not to work with you, don’t take it personally, I’m a unix geek, we do that sometimes.

You can get dmg2img here.

You’ll have to compile and install it, then you can run it like this:

dmg2img -i filename.dmg -o filename.out.dmg

Then you’ll be able to mount it normally on the loopback like this:

mount -t hfsplus -o loop /path/to/filename.out.dmg /path/to/mountpoint

Hopefully this will help someone who has the same issue I did with mounting a compressed dmg file from Mac OS X

iptables -t nat -A OUTPUT -p tcp -m owner –dport 80 –uid-owner proxy -j ACCEPT
iptables -t nat -A OUTPUT -p tcp -m tcp –dport 80 -j DNAT –to-destination 127.0.0.1:3128

This is the first step to securing a machine for kids to use as a “safe” web surfing machine.  Squid does the transparent proxy, but it’s dansguardian that makes it filter content that you might not want your kids to see.  There is a lot of documentation listed on the site on how to configure various pieces, but there was nothing that showed how to configure iptables for a stand alone machine.

All you have to do is simply edit the file /etc/ssh/sshd_config and add 1 line:

ClientAliveInterval 300

That’s it. Add that line to the bottom of your sshd_config file, save it, and then restart ssh. This option will cause sshd to send a keepalive across an idle connection every 5 minutes. This prevents the router from timing out the NAT connection, and you can happily idle as long as you need to. This option should be used with care, it’s never a good idea to leave a login session open on a computer that is not secure. As long as you aren’t lazy and leave your computer unattended where someone could use your session, you should be safe. Never, ever, ever leave yourself logged in as root on a server for longer than absolutely necessary. This is just plain common sense, but I can’t stress it enough. I have seen too many “pranks” played on people who did this out of pure laziness. Whenever you are using root, do what you have to do and exit the shell. If you want to stay idle, do it as an unprivileged user.

Having ssh timeout when you are not quite done working but still idle for whatever reason can be really annoying. This small fix should make things much more bearable for people that work like I do. I’m glad I finally took the time to research this issue, and I share it here so that others can learn from my discoveries. Enjoy.

Installing Linux was just as easy as it is on Parallels, with the same issues I’ve had with the kernel in Ubuntu Server edition. I figured out how to fix that on Parallels and the same thing applies here, simply install the generic kernel after you install the base OS and you’re good to go. VirtualBox doesn’t support Intel’s VT-x technology, so it doesn’t run quite as nicely as Parallels. As a matter of fact it pegs my CPU usage at close to 100% while any disk activity is happening. This is not a good sign for hardcore use. The performance difference between VirtualBox and Parallels is noticeable. VirtualBox is lacking some functions on OS X, including host networking. Due to VMware and Parallels I’ve come to expect certain functions and features from a virtualization solution, and that puts VirtualBox at a disadvantage.
VirtualBox has potentional to be a good competitor but it lacks performance and features that others have. Reading their website one of the best features they offer in the closed-source version is a built-in RDP server. That is a very interesting and useful feature. That could seriously hurt VMware and Parallels both if VirtualBox can only catch up on the other features. The high cpu usage issue I had would make running multiple virtual machines too much of a strain on a system. I’m optimistic that if they can get their features in line with the competition they will be a major player in the virtualization arena. I’m looking forward to the next release, but I am not going to be using VirtualBox on a regular basis yet.