FOSDEM 2005: Free and Open source Software Developers' European Meeting Matthew Grove DSG Seminar 1 st March 2005

1 Outline Presenting some topics which were presented at FOSDEM that relate to DSG’s research. Four short talks: –Wikipedia, –Debian Release Cycle, –The Linux Kernel, –Linux Kernel Device Mapper.

2 Wikipedia Wikipedia is a Web-based free content encyclopedia that is openly edited and freely readable. It is interesting to us because of our work writing portals.

3 Some Facts About Wikipedia 187 independent language editions sponsored by the non-profit Wikimedia Foundation, 80 million hits per day, 1.3 million articles, Wikipedia is run by MediaWiki open source software, 52 servers in several data centers, 1 part time member of staff :)

4 Wikipedia Growth

5 Wikipedia Sub Projects Wikipedia - free-content encyclopedia, Wikiquote - free online compendium of quotations, Wikibooks - collection of open-content textbooks, Wikisource - repository of source texts, Wikimedia Commons - provides a central repository for free images, music, sound, video, used in any Wikimedia project, Wikispecies - free directory of species, Wikinews - free-content news source, Wiktionary - free multilingual dictionary.

6 Wikipedia Problems Wikipedia is generally perceived not not be entirely credible, Regardless of whether it is credible or not, the issue has become the acceptance that people generally perceive it not to be credible, The popularity means they need to add hardware and write software, both of which are hard to do, Spam - defacing a site by wrecking it (obscene pictures or deleting content) or adding advertising, “Revert wars”.

7 The Debian Release Cycle An explanation of how Debian produce a new stable release of their distribution from the testing branch, We run Debian Sarge (Testing) on all DSG servers.

8 Debian Releases ??-- Etch, release date unknown, Sarge, partially "frozen" July 2004, expected release in 2005, Woody, July 2002, Potato, August 2000, Slink, March 1999, Hamm, July 1998, Bo, June 1997, Rex, December 1996, Buzz, June 1996.

9 Debian Main Branches Unstable Testing Stable Experimental

10 Simplified Package Lifecycle Developer Unstable Testing Frozen Stable Experimental Developer Incoming Automated Manual

11 The Path To Testing Must have been in unstable for the appropriate length of time, Must not have a greater number of "release- critical" bugs filed against it than the current version in testing, Must be compiled for all architectures slated to release, Must be a package for an architecture that is slated to release, Must not depend on versions of any packages which do not meet the above conditions.

12 From Testing To Stable 1.Start freezing the Testing branch - increase the propagation delay to reduce risk of adding bugs, 2.Proper freeze - only bug fixes make it through, 3. When all release critical bugs are fixed the new stable is released.

13 Where We Are Now Number of bugs concerning the next release (excluding ignored and not-in-testing): 117

14 The Linux Kernel How the current Linux Kernel (2.6) is being developed, The DSG runs 2.6 on servers, which use SATA and all of the desktops, We still use 2.4 on SCSI and PATA servers.

15 Some 2.6 Trees Stable (also known as vanilla or official), maintained by Linus, -mm is Andrew Morton’s patch tree, –He has been working on Linux since did some ext3 stuff and the low latency patch, –Frequently more experimental in nature than the official series, –Likely to end up maintainer of ac is Alan Cox’s patch tree, –He has worked on the kernel since 2.0, seen by many as the number two to Linus, –-ac is more conservative than –mm, –Alan is currently the maintainer of 2.2.

16 The Old Development Model There was a stable kernel (2.2) which just had bug fixes, And a development kernel (like 2.3) which all the new features were added to.

17 The New Development Model No unstable tree (yet), New code gets put into –mm by Andrew, After testing Linus puts some of it into 2.6.x, Alan uses 2.6.x and picks patches to make it more stable and fix bugs.

18 Effect Of The New Model There is a longer time between stable tree releases than there used to be (so security and bug fixes take longer to appear), -ac is probably more stable than the vanilla kernel, -mm has more bleeding edge features.

19 What Alan Cox Thinks 2.6.x.y - point releases to do the security updates and bug fixes while we wait for a new stable kernel release, The counter argument is that the Linux distributions (vendors) will do the patching for you and you should use their kernel. –However people like using the stable tree as we trust Linus more than our vendors and picking and mixing patches ourselves can be hit and miss. Perhaps we should be using –ac for now?

20 Device Mapper A brief introduction to the Linux Kernel Device Mapper and LVM2 with some examples.

21 An Introduction To LVM The Device Mapper is a the kernel driver for virtualising storage. It allows you to use LVM2: – LVM2 is the second implementation of Logical Volume Management on Linux. – LVM allows you to create virtual volumes (and volume groups) which can be resized and moved around dynamically.

22 Simple Example (Part 1) I have a small hard drive which I install Linux on. I make an educated guess as to what size partitions I need. /boot /dev/hda1 10 Megabytes swap /dev/hda2 256 Megabytes / /dev/hda3 2 Gigabytes /home /dev/hda4 6 Gigabytes

23 Simple Example (Part 2) My root partition becomes full and I want to install some software, but there is still space on other partitions, my options are: 1.Reformat the disk, change the partitioning scheme and reinstall. 2.Buy a new disk and figure out some new partitioning scheme that will require the minimum of data movement. 3. Set up a symlink farm on / pointing to /home and install the new software on /home.

24 If I had used LVM my drive would have looked like this: I could reduce /home by 1 GB and add it to the root partition. In the future if I bought a new disk I could add it to the existing volume group and extend the /home logical volume to include the new disk. Simple Example (Part 3) /boot /dev/hda1 10 Megabytes swap /dev/vg00/swap 256 Megabytes / /dev/vg00/root 2 Gigabytes /home /dev/vg00/home 6 Gigabytes

25 Device Mapper Targets Linear, Striped, Crypt, Mirrored, Snapshot, Multipath.

26 Summary It will be be interesting to see if Wikipedia is a success or whether it turns into the new Usenet, Debian Sarge will be released when it’s ready, We should think about using the –ac patch to the stable kernel branch unless they adopt 2.6.x.y, LVM2 can help you whether you have 800MB or 800GB of storage.

27

28 Wikipedia, The Debian Release Cycle, The Linux Kernel, Linux Kernel Device Mapper. Links