Creating DMG Files Without MacOS X

I’ve put together a script for creating DMG files without using OS X…it requires Linux, I’ve tested it on Kubuntu 7.10 but it should work on anything recent. The process will also be Wiki’d, but in the meantime, instructions are below for the curious!

Run the following commands:

# This gets and builds a patched version of Apple's diskdev_cmds package which will work on Linux
tar xzf diskdev_cmds-332.14.tar.gz
bunzip2 -c diskdev_cmds-332.14.patch.bz2 | patch -p0
cd diskdev_cmds-332.14
make -f Makefile.lnx

# Create symlinks to the mkfs and fsck commands for HFS+
sudo cp newfs_hfs.tproj/newfs_hfs /sbin/mkfs.hfsplus
sudo cp fsck_hfs.tproj/fsck_hfs /sbin/fsck.hfsplus

# Get and enable the hfsplus kernel module
sudo apt-get install hfsplus
sudo modprobe hfsplus

Now that's done, you can use the following handy bash script (must be run as root) I've written to create a DMG file which contains the contents of a directory you specify on the command line.


# DMG Creation Script
# Usage: makedmg <imagename> <imagetitle> <imagesize (MB)> <contentdir>
# imagename: The output file name of the image, ie foo.dmg
# imagetitle: The title of the DMG File as displayed in OS X
# imagesize: The size of the DMG you're creating in MB (Blame Linux for the fixed size limitation!!)
# contentdir: The directory containing the content you want the DMG file to contain
# Example: makedmg foo.dmg "Script Test" 50 /home/jon/work/scripts/content
# Author: Jon Cowie
# Creation Date: 02/04/2008

if [ ! $# == 4 ]; then
	echo "Usage: makedmg <imagename> <imagetitle> <imagesize (MB)> <contentdir>"

	if [ ${USER} != "root" ]; then
		echo "makedmg must be run as root!"
		echo "Creating DMG File..."
		dd if=/dev/zero of=${OUTPUT} bs=1M count=$FILESIZE
		mkfs.hfsplus -v "${TITLE}" ${OUTPUT}

		echo "Mounting DMG File..."
		mkdir -p ${TMPDIR}
		mount -t hfsplus -o loop ${OUTPUT} ${TMPDIR} 

		echo "Copying content to DMG File..."

		echo "Unmounting DMG File..."
		umount ${TMPDIR}
		rm -rf ${TMPDIR}

		echo "All Done!"

Hope it’s useful!

Groovy Virtualisation Hardware

I came across some interesting news today (Linky) that said Neterion is releasing a fairly hardcore network card designed for offloading VM Network management from the Hypervisor. I think this has the potential to be quite an interesting field in the future…in small scale Virtualisation deployments it’s not such a big deal that the Hypervisor has to do all the legwork for IO, but when you scale up to much larger deployments, network IO has the potential to be a significant bottleneck. You can mitigate this somewhat by utilising the physical network card, but this in turn shifts the load onto the host OS. It should be interesting to see in future what else hardware manufacturers come up with along similar lines: VM aware disk & memory controllers, for example…Intel have already made strides towards VM aware CPUs with VT as well.

Being a rather geeky type, I’m quite excited to see what all these clever hardware types come up with in the next few years…wouldn’t it be nice to be able to buy a server full of VM aware kit which lets you run multiple VMs as quickly as if you were using just one host OS? I can’t see virtualisation going away any time soon, it’s just too damn useful – so I reckon this might be something just around the corner.

New Start

So with my pending move to a Web 2.0 friendly company I thought I probably ought to start updating my blog, something I’ve been meaning to do for ages! I’m going to be working as a System Engineer for Trampoline Systems who are doing some very funky stuff to allow large organisations to enable more natural communication…the theory is that most organisations make humans try to communicate like computers, which stifles our natural instincts. Anyway, go check them out, it’s all very exciting! In other news, 8 days until I say bye-bye to the premium rate telephony sector.

And now for some stuff I like…