Monday, October 18, 2010

Fun with customized Ubuntu distributions

At work we have an interesting problem. We are working with some companies in Taiwan. Obviously there's a language difference, but there is another difference as well. We are an Ubuntu Linux shop, and they all have Windows laptops. Periodically we have bits of test code that they need to use, and the OS gulf needs to be overcome.

My first whack at this issue was to try to use Cygwin to rebuild our tools from source on a Windows platform. But after I'd spent a few days dealing with libusb, and making not a whole lot of progress, a co-worker suggested a bootable USB stick. The Taiwanese folks get to keep their Windows laptops, but with a quick reboot they can temporarily use Linux machines just like ours. So I set about learning the art of bootable USB sticks, which in Ubuntu 9.10 is pretty painless. (This is not the case with Ubuntu 10.04. If you need to do this, stick with 9.10.)

Not to keep you in suspense, the two magical things are
  • Ubuntu Customization Kit, (sudo apt-get install uck) which produces an ISO file suitable for burning a CD or DVD which you can boot from, and
  • USB Startup Disk Creator (already present in your System>Administration menu) which puts that ISO file onto a USB stick and makes the stick bootable.
These are amazingly easy-to-use tools, given the complexity of what they're doing. In the bad old days, the Knoppix distribution existed solely for the purpose of rendering this feat possible for mortals. That said, I learned a few tricks about these things which I'll pass along here. Do NOT use Ubuntu 10.04, as there is a serious bug in that version of UCK plus a handful of annoying behavioral oddities. These are fixed in a future UCK release, but that's not available in the Ubuntu 10.04 repositories. In order to produce a USB stick which could be used with a Windows laptop to produce another bootable USB stick, I put a copy of the ISO file onto the USB stick. The instructions for copying the USB stick then go like this.
  • Boot into Windows and insert the first USB stick. Copy the ISO file somewhere memorable. Restart the laptop.
  • Boot into Ubuntu using the USB stick. Once you're booted, insert the second USB stick.
  • Bring up USB Startup Disk Creator. The original ISO file on the first USB stick (from which you are now running) will not be visible in the file system. But the Windows hard drive will be readable, so dig around in it to find the ISO file copy you just used. Use that as the source, and select the 2nd USB stick as the destination. Push the button.
  • Once that installation is complete, copy the ISO file from the Windows hard drive onto the second USB stick. Voila, a copy.
Using the first part (making an ISO image) I was able to produce a DVD with some of our tools for the Taiwanese folks to use. I set up Traditional Chinese and English as languages, with the default to boot into Traditional Chinese. But then because it had some of our source code, I encrypted this entire 725 MB file, which is ironic given that Ubuntu is open source. But there had to be a way to encrypt only the proprietary stuff.

On the next boot image I send them (which will be a USB stick, not a DVD, since USB sticks are oh so much sexier), the contents of the stick will be open source, and the proprietary stuff will be pulled down from a little tarball on some handy little server. The thing that pulls down the tarball and handles security is my little tarball runner script. The new ISO is at, and if you need to share some closed-source Linux code with people in China or Taiwan, feel free to use it.

To use this bit of cleverness, build some code on your Linux box, package it up as a tarball (including a shell script at the root level, in case you need to do installation stuff), and if necessary, encrypt it using (my tweaked version of) the Twofish algorithm found on Sourceforge. Then post it to the Internet and email the password only to your intended recipients.

If I find the time and energy, I'll package up the tarball runner and the Twofish module as a Deb package to make the installation painless.

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