The anatomy of a Linux distribution [LWN.net]

By Rebecca Sobol
August 15, 2007

The anatomy of a Linux distribution is pretty simple. It is a distribution of packages that includes a Linux kernel, bundled together to work on a given piece of hardware. There are plenty of other kernels to choose from; BSD, Hurd, Solaris, etc.; and plenty of distributions that include a similar package set. For example, the GNOME desktop looks about the same on OpenSolaris as it does on Linux.

The type of hardware may impose certain constraints. Embedded devices of all kinds run a Linux kernel, but the package set varies with the function of the device. Linux runs on a wide variety of hardware and the overall set of Linux kernels currently in use is quite large, as each distributor makes their own tweaks and twists to get the best performance on their hardware.

Most people reading this article are using some type of desktop Linux. The most common hardware is x86, but there will be many readers using x86_64, PPC, or something else entirely. Still, the packages on the desktop will be similar.

This is, perhaps, one reason why there are so many Linux distributions. That number continues to grow: over 300 on our list a couple of years ago, now it's over 500 on the list. Each one is unique in some way. Sure, they all have some type of Linux kernel, but there are older kernels and newer kernels, and kernels that support non-x86 hardware of all kinds. Some of these distributions are not maintained anymore, but the source code remains available and someone, somewhere may find it useful.

It was and still is very common to take a particular distribution and modify it until it becomes a unique distribution. Red Hat Linux used to be a very common base distribution. Now the most common base is Debian, but there are also distributions based on Red Hat Enterprise Linux, Fedora and Ubuntu. Knoppix, the original live CD, was spawned from Debian and now has dozens of spin-offs, each with their set of packages.

These days we are seeing a new explosion of custom distributions. Fedora has spins and Ubuntu has flavors. Anyway you look at it the tools to create a customized distribution are maturing and becoming more usable. While the total number of Linux distributions is not likely to shrink any time soon, we may start to see a few base distributions take over the customized desktop.

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Knoppix was not the first

Posted Aug 17, 2007 15:06 UTC (Fri) by maney (subscriber, #12630) [Link]

Back at the dawn of Linux distributions, Yggdrasil Linux was available in runs-from-CD form. Or so I understand - I have no memory of actually using it. Possibly the performance was so awful on a 386 with an external 1x CD drive that I've blocked the horror of it out of my memory. :-)

Knoppix was certainly the first live CD to catch on in a big way, but it missed being the first to run from CD by quite a few years.

Knoppix was not the first

Posted Aug 17, 2007 20:15 UTC (Fri) by giraffedata (subscriber, #1954) [Link]

Back at the dawn of Linux distributions, Yggdrasil Linux was available in runs-from-CD form. Or so I understand

I'm skeptical, because modern runs-from-CD Linuxes use modern technology: union filesystem and ramdisk or ramfs.

Years ago, I modified my system to have a read-only root filesystem and it took quite a bit of work. To this day I have to modify some packages that expect to be able to modify files in the root filesystem and I hardly ever install new versions of anything. So while Yggdrasil could certainly have done it, it would have been expensive.

Knoppix was not the first

Posted Aug 18, 2007 9:49 UTC (Sat) by csawtell (subscriber, #986) [Link]

Yggdrasil did indeed run from the CD, but 'run' took on the meaning of 'demonstrate slowly'. It was effective in that one could see what you were going to get before you installed the package. I used the Fall-95 release for quite a while and was most disappointed when it withered away and died.
I think I've still got the disk somewhere, I'm almost tempted to spin it up on modern hardware just to see what happens.

Knoppix was not the first

Posted Aug 21, 2007 4:54 UTC (Tue) by roelofs (subscriber, #2599) [Link]

I think I've still got the disk somewhere, I'm almost tempted to spin it up on modern hardware just to see what happens.

I'm not sure I have an Yggdrasil CD (though I still have some MCC floppies...), but I did try booting Knoppix ca. 2003 on a 1995 Pentium 166(?) and 32 MB of RAM. Whoo boy, what a mistake... Took 20 minutes to boot and pretty much thrashed continuously no matter what one tried. :-)

Old distros on modern hardware tend not to fare too well simply because they don't recognize much (any?) of the hardware. When the original distros came out, ISA/EISA/VLB were king, and USB didn't exist; now it's all PCI/PCI-x/AGP/USB2--i.e., most of your basic I/O may not show up, which makes interactions...difficult. ;-) Of course, if it does boot, it should scream... (I still occasionally boot a 16MB Pentium-75 laptop running Slackware 3.4, I think. It's quite usable.)

Greg

Will Virtual Appliances replace **Some** custom distributions?

Posted Aug 23, 2007 12:27 UTC (Thu) by JimCallahan (guest, #46959) [Link]

There will always be a need for the major primary Linux distributions, but might some of the downstream Linux distribution bundling be better served by a download-able virtual appliance (image to be run on a virtual machine) rather than a an iso image an install CD/Live CD?

Virtual appliances would seem to be helpful where the primary purpose of the distribution is to distribute installed versions of desktop or server applications.

On the server side, there are already virtual appliances for LAMP web servers including application servers such as Drupal or Joomla, blogging software or even Wiki software.

On the desktop side, one could see distributions such as Edubuntu or Quantian becoming virtual appliances (minus the feature to convert a computer lab into a super computer). Academic, Scientific or engineering managers could have a standard university or corporate desktop and a virtual machine workstation running statistical, mathematical or engineering software. Managers could discharge their routine management responsibilities on the standard desktop (that's what it is for) and then analyze a data set or prepare a scientific paper using the specialized tools on the virtual appliance workstation.

Virtual appliances would not work for Linux distributions intended as rescue CDs or for converting a networked computer lab into an ad-hoc supercomputer.

What do you think?

Is there a more neutral term than VMWare's "Virtual Appliance?"
If existing downstream Linux distributions adopt this format should LWN and DistroWatch cover them?

Jim Callahan
Orlando, FL

Will Virtual Appliances replace **Some** custom distributions?

Posted Aug 23, 2007 12:57 UTC (Thu) by JimCallahan (guest, #46959) [Link]

Imagine this scenario, a researcher/manager has a Windows PC at work and uses Microsoft Office (MS Word, MS Excel, MS Powerpoint & MS Access) and Lotus Notes, while having an Apple PC at home using iLife (Garage Band, iPhoto, iMovie, iWeb) and iWork.

On both the Windows work PC and Apple Mac home PC the manager runs VM software (either proprietary VMWare or open source XEN).

The manager keeps professional tools on a 4 gigabyte keyring USB drive.

The manager's profession might be bioinformatics, economics, statistics, engineering, chemistry, education or any other field that has a rich set of open source tools.

The tools run in their own (guest) operating system environment distinct from the primary (host) operating systems in use at home or work. The IT Department likes the fact that only the virtual machine software hits the real Windows PC registry.

I expect the above scenario will be commonplace in less than 3 years! By 2010 we will all be running multiple OS in virtual machines. Look at your Sunday newspaper adds -- all the big box retailers are advertising dual core notebook computers with a gigabyte of RAM for $500.

Given the recent VMWare IPO (the largest since Google) can we doubt that we are entering an era when virtual machines will become ubiquitous?

Of course their is always the "Grandmother test." Right now I am suggesting to my mother that her next computer should be an Apple Mac, use iLife to manipulate photos and run her remaining Windows apps (AOL, TurboTax?) in VMWare Fusion.

Yup, VMs are coming...

Jim Callahan
Orlando, FL