Building Your Own Live CD
You've probably heard of Knoppix, the Debian-based distribution that squeezes 2GB of applications on a single standalone CD. It's been used as a Linux demonstration tool, a rescue disk and even as a Debian installer. It's inspired a small raft of related projects, ranging from CDs containing Knoppix, plus or minus a few extra packages, to complete re-architectures of the system.
I recently set out to produce a live CD for a product demonstration. I started by taking the Knoppix CD apart to see how it ticked, and I ended up with a Makefile and a few ancillary files that are clearly Knoppix-inspired but have little derived code. This is what I learned.
If you put the Knoppix CD in a CD-ROM drive and mount it, you soon notice that it doesn't look much like an ordinary Linux installation. There are a few graphic files and a free music track, but no init, no /dev and no /bin. The magic is in the big file called /KNOPPIX/KNOPPIX, an ISO9660 filesystem image compressed for the cloop device.
The standard loop device in the kernel allows you to access a file in some filesystem as if it were a device; requests for blocks of the device are mapped to requests for blocks in the underlying file. Because you can mount the device, this effectively means you can create images of filesystems and access them as if they were real hardware disks. If you downloaded Knoppix from the Net, you have an ISO9660 image that can be loop mounted to look at its contents:
# mkdir /tmp/knoppix-cd # mount -o loop -r \ $HOME/KNOPPIX_V3.3-2003-09-24-EN.iso /tmp/knoppix-cd
The cloop compressed loop device takes this a step further. In this adaptation of the loop device, each block is compressed with gzip and transparently decompressed when it's accessed. /KNOPPIX/KNOPPIX is an image for this device that is mounted during startup—this is how Knoppix gets 2GB onto a 650MB CD.
You don't need to install cloop in your usual kernel if you simply want to look around the inner filesystem. Install the cloop-utils package and use extract_compressed_fs, as shown below. You need about 2GB of free space in /var/tmp or wherever you decide to put the image:
# mkdir /tmp/knoppix-cloop # extract_compressed_fs \ /tmp/knoppix-cd/KNOPPIX/KNOPPIX \ >/var/tmp/KNOPPIX-cloop # mount -o loop /var/tmp/KNOPPIX-cloop \ /tmp/knoppix-cloop # find /tmp/knoppix-cloop -print
You can look, but you can't touch—the ISO9660 filesystem is read-only. To modify the distribution, you first need to copy both filesystem images to ordinary directories:
# mkdir $HOME/my-knoppix-tree \ $HOME/my-knoppix-cd-tree # tar -C /tmp/knoppix-cloop -cf - . | \ tar -C $HOME/my-knoppix-tree -xvpf - # tar -C /tmp/knoppix-cd -cf - . | \ tar -C $HOME/my-knoppix-cd-tree -xvpf - # umount /tmp/knoppix-cd /tmp/knoppix-cloop
Now, you can hack away to your heart's content. The most convenient way to do this is to change root into the Knoppix inner tree using the chroot command:
# mount -t proc none $HOME/my-knoppix-tree/proc # cp /etc/resolv.conf \ $HOME/my-knoppix-tree/etc/resolv.conf # chroot $HOME/my-knoppix-tree /bin/sh
From here, you can use all the usual Debian package management commands (dpkg, apt-get and so on) to install or delete whatever you like. When you're done, exit the chroot and unmount proc, unless you want your development system's process list immortalised on CD. Then, use create_compressed_tree and mkisofs to create the inner and outer images:
# mkisofs -L -R -l -V "KNOPPIX ISO9660" -v \ -allow-multidot $HOME/my-knoppix-tree | \ create_compressed_fs - 65536 > \ $HOME/my-knoppix-cd/KNOPPIX/KNOPPIX # mkisofs -l -r -J -V "KNOPPIX with local stuff" \ -hide-rr-moved -v -b KNOPPIX/boot-en.img \ -c KNOPPIX/boot.cat -o knoppix.iso \ $HOME/my-knoppix-cd
Finally, burn knoppix.iso to a CD-ROM and boot it. If you prefer, you can test without burning by using Bochs or VMware.
This simple approach starts to break down, however, when you want more extensive customizations. For example, if you want X to start a particular window manager but don't want to use all of GNOME or KDE, you have to edit the script yourself. This isn't hard to do, but it means that you've essentially forked Knoppix. When a new Knoppix version comes out, you'll have to do it again. In addition, if you intend to sell your Knoppix-based CD commercially, you need to remain compliant with the licenses of all the software you distribute, which means knowing exactly what's on it. The Knoppix version I looked at contained some files that weren't from Debian packages, and sometimes they weren't even free software.
So, is there some other place we could start? Happily, yes. Between the efforts of Progeny, which donated its installer to the Debian Project; Klaus Knopper, the author of Knoppix and the creator of the cloop device; and other Debian developers who are working on adding his custom code into the main Debian repository—today we can put together a passable live CD system from scratch using only Debian packages. The rest of this article describes how.
Practical Task Scheduling Deployment
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
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- Managing Linux Using Puppet
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- Doing for User Space What We Did for Kernel Space
With all the industry talk about the benefits of Linux on Power and all the performance advantages offered by its open architecture, you may be considering a move in that direction. If you are thinking about analytics, big data and cloud computing, you would be right to evaluate Power. The idea of using commodity x86 hardware and replacing it every three years is an outdated cost model. It doesn’t consider the total cost of ownership, and it doesn’t consider the advantage of real processing power, high-availability and multithreading like a demon.
This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide