I first read about Y Combinator while browsing Paul Graham s website. I am a huge fan of his and have tried many times to bring him to Brazil for FISL (unsuccessfully so far). By that time I was updating a lecture of mine where I quote something from his Hackers and Painters essay and sudenly I noted an YC link on the left, and decided to click to learn what was that. Y Combinator is a venture capital firm to help start-ups. It was built on the concept that not much money is needed for first-stage start-ups ( from idea to company , as they call it). Quite a concept! I lost track of it until yesterday, when I read this blog post summarizing one of its events for start-ups. I found it amazing how far it came in such little time. They ve already funded about 100 start-ups, some of them really interesting. Of those presented in that post, Posterous is one I found most interesting. They create instant blogs just by sending emails to some address. There s no sign-up procedure Just send the email with any attachments and voil . There you have: a new blog. Many others are really interesting (PollEveryWhere, IDidWork, Frogmetrics, just to name a few), so I really suggest reading that post. I think Y Combinator is another great idea from Paul Graham, and I will be following it more closely, as a way to keep myself updated Who knows maybe I can get them to come to FISL to present that! ;-)

...was brought to you by the letters A, O and K!

Getting the appointment with the oncologist is something we've been trying to do for months. So I'm pleased with the outcome that after the meeting and the review of the scans, she sees no need to radiation and such.

Yay!

Also in the good news category is that she's not seen a genetic component to an osteoblastoma. So while I will have to go for scans every 6 months for the next while and yearly probably forever, there's no need for the kids to do so.

(Oy. Kids. Plural. Still getting used to that...)

As always, thanks everyone for hugs, thoughts, and prayers. Next update: October, when I get an MRI, a bone scan, and have my final visit with this surgeon before the move.

I've updated my simple Simple SDL based perl game, so that:

• It has a name.
• It has an intro screen which uses that name!
• It has multiple balls.
• It gets harder, ie. more balls are added.
• The collision detection is much improved.

I still need to work on the rebound-angle but otherwise it is as complete as it will probably ever become. It would also be nice if the balls could collide with each other, and be different colours.. Regardless it was a fun diversion for a few hours, and probably tells me that I shouldn't attempt to waste more time doing gamy things, and that maths is too hard for me these days. ObQuote: Interview with the vampire

The Debian Live team is pleased to announce the first beta of Debian Lenny's Live images. Although we missed releasing images for Etch along with the installer images, we are now prepared to release live images within the regular Lenny release process. This is the first official release of Debian Live and the whole team has been working hard during the past 2.5 years to make Debian's own live systems become a reality. Nevertheless, we do need your help to find more bugs and improve the live systems, so please try them out. The images are available at:

	http://cdimage.debian.org/cdimage/lenny_live_beta1/

Please also have a look at the known issues listed below. Main features 100% Debian The build process of Debian Live basically consists of creating a Debian chroot, installing one or more kernels along with live-initramfs (a set of hooks into initramfs-tools for handling booting from read-only media) and generating a bootable image from that. This process is handled by live-helper, a collection of shell scripts that allow us to automate and customize this process. Considerable care is taken to ensure that the resulting live system is not tainted by the host system and that installed packages are not modified morethan absolutely necessary. This ensures that Debian Live really is Debian, and not "just another" a Debian-based live system. Flavours Although live-helper is a toolkit to produce your very own live systems with only a few steps, we also provide prebuilt images that are meant to be used as reference systems for end-users. Currently, this consists of the three major desktop environments (GNOME, KDE and Xfce), as well as a small 'standard' image without a graphical environment. For the desktop environments, package selection is performed by 'tasksel' with the respective desktop task, whilst the 'standard' image contains only packages of "Priority: standard" or greater, notwithstanding a handful of live-specific packages (console-common, eject, file, kbd, live-initramfs, locales, sudo and vim-tiny). Image types Debian Live offers prebuilt images for CD/DVD discs, USB sticks (or any HD-media-like device), tarballs (for PXE netboot) as well as a bare squashfs image to boot from the web directly. Live Magic Live Magic is an GUI frontend around the live-helper scripts, offering a subset of the features of live-helper in an easy-to-use graphical user interface. live-magic 1.0 was recently uploaded to sid and is the recommended version. It currently supports 7 languages. Live Installer Live Installer is a special udeb for the Debian Installer that (optionally) replaces a part of d-i in order to install the system from the live image instead of to bootstrapping it from .deb packages. This way, a live system can be easily installed to the harddisk, ensuring that the look and feel of the installation (including preseeding) works the same as the regular installer process. Unfortunately, live-installer does still have a few minor bugs left and is thus not included in our builds yet; we hope to be able to include it in the next beta. Known issues in this release

• The prebuilt images for gnome-desktop and kde-desktop are a bit too big to fit on a CD. Although the automatic installation of Recommends was disabled to build the images, they are still too big. This will need further tweaking as they are supposed to fit with the next beta.
  
  
• The rescue flavour, containing system rescue and forensic related packages, is missing in this beta release.
  
  
• There will be a DVD image with the next beta that includes all three desktop environments so that you can choose at boot time which system you would like to start.
  
  
• Due to time constraints, the prebuilt images for Beta1 are only covering i386 and amd64; with the next beta, powerpc and sparc will follow (if you wish to test these architectures earlier, please build them yourself).
  
  
• The new desktop artwork is not yet included.
  
  
• The syslinux menu is still the old, prompt-based one. A freshly made new syslinux vgamenu using the official lenny desktop artwork is on the way (the same as d-i media will use in Lenny).
  
  
• No live-installer included yet (if you wish to test live-installer earlier, please build it yourself).
  
  
• No win32-loader included yet.
  
  
• Sid packages used - At the time of building the live images, both live-helper 1.0.0-1 and live-initramfs 1.139.1-1 from sid were used. Since the latter has not yet migrated to testing, it was included manually as a local package. This is undesirable, as the release is supposed to be self-contained - however, it is just a convenient workaround as both were granted freeze exception and will migrate soon.

Plans for next Beta release We are looking forward to upload Beta2 in about two weeks from now (maybefollowed by a third beta) with one final RC after that which should be identical to the final release. Some more details about the open things we would like to address in Beta2 and later can be found at the wiki page. The Debian Live team is still looking for more contributors for new features (post-lenny, though) as well as documentation writers for the manual (always). If you care about live systems, please join and help! Thanks Last but not least, our thanks goes to everyone who has contributed and to all maintainers that have kindly fixed live-specific bugs in their packages.

Some interesting events that I’ve heard about recently, with a bit of a focus on software, cooperatives and the South-West:-

• Bristol Knowledge Unconference: Friday 5th September 2008 *
• Tour of Britain, Burnham-on-Sea, Somerset, Tuesday 9th September - other UK locations 7-14 September, itv4 7pm highlights daily *
• NoseRub DevCamp, Cologne, 13.-14. September 2008
• BathCamp, Bath, Somerset, 13-14th September
• Bristol Anarchist Bookfair, St Werburgh’s Centre, Bristol, 13-14th September
• Software Freedom Day, Global, 20 September 2008
• Scripting Enabled, London, 19th and 20th September
• Listening to the Social Entrepreneur, London Docklands, 9 Oct 2008 *
• LinuxWorld, London Olympia, 23-25 Oct 2008 *
• enterprise week, UK, part of Global Entrepreneurship Week, 17-23 November
• Cooperatives-SW/RISE Trade Fair, Bristol, 1st December *

I’m pretty sure I’ll go to the *d ones - which others do you think I should go to? Will you be at any of these? Any comments to make on/to any of them? Any more to add to the list?

The Problem: A problem with virtual machines is the fact that one rogue DomU can destroy the performance of all the others by inappropriate resource use. CPU scheduling is designed to allow reasonable sharing of computational resources, it is unfortunately not well documented, the XenSource wiki currently doesn’t document the “credit” scheduler which is used in Debian/Etch and CentOS 5 [1]. One interesting fact is that CPU scheduling in Xen can have a significant effect on IO performance as demonstrated in the paper by Ludmila Cherkasova, Diwaker Gupta and Amin Vahdat [2]. But they only showed a factor of two performance difference (which while bad is not THAT bad). A more significant problem is managing virtual memory, when there is excessive paging performance can drop by a factor of 100 and even the most basic tasks become impossible. The design of Xen is that every DomU is allocated some physical RAM and has it’s own swap space. I have previously written about my experiments to optimise swap usage on Xen systems by using a tmpfs in the Dom0 [3]. The aim was to have every Xen DomU swap data out to a tmpfs so that if one DomU was paging heavily and the other DomUs were not paging then the paging might take place in the Dom0’s RAM and not hit disk. The experiments were not particularly successful but I would be interested in seeing further research in this area as there might be some potential to do some good. I have previously written about the issues related to swap space sizing on Linux [4]. My conclusion is that following the “twice RAM” myth will lead to systems becoming unusable due to excessive swapping in situations where they might otherwise be usable if the kernel killed some processes instead (naturally there are exceptions to my general rule due to different application memory use patterns - but I think that my general rule is a lot better than the “twice RAM” one). One thing that I didn’t consider at the time is the implications of this problem for Xen servers. If you have 10 physical machines and one starts paging excessively then you have one machine to reboot. If you have 10 Xen DomUs on a single host and one starts paging heavily then you end up with one machine that is unusable due to thrashing and nine machines that deliver very poor disk read performance - which might make them unusable too. Read performance can particularly suffer in a situation when one process or VM is writing heavily to disk due to the way that the disk queuing works, it’s not uncommon for an application to read dozens or hundreds of blocks from disk to satisfy a single trivial request from a user, if each of these block read requests has to wait for a large amount of data to be written out from the write-back cache then performance will suck badly (I have seen this in experiments on single disks and on Linux software RAID - but have not had the opportunity to do good tests on a hardware RAID array). Currently for Xen DomUs I am allocating swap spaces no larger than 512M, as anything larger than that is likely to cause excessive performance loss to the rest of the server if it is actually used. A Solution for Similar Problems: A well known optimisation technique of desktop systems is to use a separate disk for swap, in desktop machines people often use the old disk as swap after buying a new larger disk for main storage. The benefit of this is that swap use will not interfere with other disk use, for example the disk reads needed to run the “ps” and “kill” programs won’t be blocked by the memory hog that you want to kill. I believe that similar techniques can be applied to Xen servers and give even greater benefits. When a desktop machine starts paging excessively the user will eventually take a coffee break and let the machine recover, but when an Internet server such as a web server starts paging excessively the requests keep coming in and the number of active processes increases so it seems likely that using a different device for the swap will allow some processes to satisfy requests by reading data from disk while some other processes are waiting to be paged in. Applying it to Xen Servers: The first thing that needs to be considered for such a design is the importance of reliable swap. When it comes to low-end servers there is ongoing discussion about the relative merits of RAID-0 and RAID-1 for swap. The benefit of RAID-0 is performance (at least in perception - I can imagine some OS swapping algorithms that could potentially give better performance on RAID-1 and I am not aware of any research in this area). The benefit of RAID-1 is reliability. Now there are two issues in regard to reliability, one is continuity of service (EG being able to hot-swap a failed disk while the server is running), and the other is the absence of data loss. For some systems it may be acceptable to have a process SEGV (which I presume is the result if a page-in request fails) due to a dead disk (reserving the data loss protection of RAID for files). One issue related to this is the ability to regain control of a server after a problem. For example if the host OS of a machine had non-RAID swap then a disk failure could prevent a page-in of data related to sshd or some similar process and thus make it impossible to recover the machine without hardware access. But if the swap for a virtual machine was on a non-RAID disk and the host had RAID for it’s swap then the sysadmin could login to the host and reboot the DomU after creating a new swap space on a working disk. Now if you have a server with 8 or 12 disks (both of which seem to be reasonably common capacities of modern 2RU servers) and if you decide that RAID is not required for the swap space of DomUs then it would be possible to assign single disks for swap spaces for groups of virtual machines. So if one client had several virtual machines they could have them share the same single disk for the swap, so a thrashing server would only affect the performance of other VMs from the same client. One possible configuration would be a 12 disk server that has a four disk RAID-5 array for main storage and 8 single disks for swap. 8 CPU cores is common for a modern 2RU server, so it would be possible to lock 8 groups of DomUs so that they share CPUs and swap spaces. Another possibility would be to have four groups of DomUs where each group had a RAID-1 array for swap and two CPU cores. I am not sure of the aggregate performance impact of such a configuration, I suspect that a group of single disks would give better performance for swap than a single RAID array and that RAID-1 would outperform RAID-5. For a single DomU it seems most likely that using part of a large RAID array for swap space would give better performance. But the benefit in partitioning the server seems clear. An architecture where each DomU had it’s own dedicated disk for a swap space is something that I would consider a significant benefit if renting a Xen DomU. I would rather have the risk of down-time (which should be short with hot-swap disks and hardware monitoring) in the rare case of a disk failure than have bad performance regularly in the common situation of someone else’s DomU being overloaded. Failing that, having a separate RAID array for swap would be a significant benefit. If every process that isn’t being paged out could deliver full performance while one DomU was thrashing then it would be a significant benefit over the situation where any DomU can thrash and kill the file access performance of all other DomUs. A single RAID-1 array should handle all the swap space requirements for a small or medium size Xen server One thing that I have not tested is the operation of LVM when one disk goes bad. In the case of a disk with bad sectors it’s possible to move the LVs that are not affected to other disks and to remove the LV that was affected and re-create it after removing the bad disk. The case of a disk that is totally dead (IE the PV header can’t be read or written) might cause some additional complications.

• [1] http://wiki.xensource.com/xenwiki/Scheduling


• [2] http://www.cs.ucsd.edu/~dgupta/papers/per07-3sched-xen.pdf


• [3] http://etbe.coker.com.au/2008/05/22/xen-and-swap/


• [4] http://etbe.coker.com.au/2007/09/28/swap-space/

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I’d been having problems connecting my laptop to my router to the Phone Coop using a new network cable that I laid under the floor just after the new heating system was installed. It’s a 1970s building - cat-5 wasn’t installed with the original wiring and mains homeplug networking is tricky on this wiring layout. The growing number of people with WiFi and video senders on my hillside (70% of UK users “never or rarely switch off their broadband wireless routers”) seems to be causing more interference and slow-downs, so it seemed worth installing a wired connection while the floors were up. The connection seemed to work fine, but then kept stopping for 20 seconds at a time - that’s just long enough to break network connections, but barely long enough to start up debugging tools, let alone get useful output. I was pretty sure the cable wasn’t at fault - Paul tested it with his fancy test gear when he completed the wiring for me. That left the hardware: my much-hated Belkin F5D7630 and the Realtek 8139 in the bizarre Compaq Evo N1015v. I’ve still not got around to replacing that Belkin and it’s been behaving itself well enough recently, while the Compaq has run smoothly once I actually got Linux onto it. I found the end of this Ubuntu Forums thread which pointed to this archlinux bulletin board thread which suggested pnpbios=off pnpacpi=off in the boot options. After adding that, the 20-second network pauses have stopped. But why? The ACPI and BIOS in this laptop are generally troublesome (and it looks like this also happens on some Presarios), but what in particular is going wrong this time? Will I suffer ill effects from switching off PNP options? Time will tell, I guess.

Rhonda, have you reported the SCons problems you’ve found to either the Debian mantainer or upstream? That’s much more likely to be an effective way of improving things than blogging about them. For what it’s worth the .scons files are a bug in the SCons core AFAICT (it needs a distclean equivalent that doesn’t appear to be there; I suspect nobody has asked for it before) and the failure to clean up other generated files will be bugs in the support for whatever tool is being used to do the build.

I've written a simple perl script using SOAP to add some useful data to the RC bug list (or any list of bugs). It can easily be extended but right now it supports simple things like the date the bug was filed, short description of the package, the name of the maintainer, the most recent upload data, the debtags for the package, apt-cache policy data and whether the bug is already tagged pending.
Zenity presents this info in a question dialog, clicking OK loads the bug and the PTS in your browser using 'sensible-browser'.
Clicking cancel offers a new zenity dialog asking for the next bug number. (Click Cancel there to end the script.)
Code: http://linux.codehelp.co.uk/rc-zenity.pl (GPLv3 or later)
POD: http://linux.codehelp.co.uk/rc-zenity.html (easily convertible into a manpage using pod2man)
If you like it, use it.
If lots of people like it, maybe it can go into an existing package.
If I've duplicated another script that I just didn't know about, tell me.

It's not exclusively for RC bugs, it could work with any bug list or be modified to only look for particular severity settings.
Thanks to Don Armstrong for making debbugs so accessible using SOAP. The debbugs SOAP implementation is just so straightforward with a whole load of useful data returned without needing repeated queries, it makes scripts like this really satisfying.

After watching the Packaging with version control systems talk by Martin F. Krafft ( thanks debconf video team ). I really want to update my packaging workflow, Martin's workflow seems too complicated to me. I'd like to have a simplified version for my packages. The question is though which VCS do I choose, I have experience of bzr but have never used git or mercurial. Changing my packaging workflow is not something I want to be doing too often, so I would like to make the "right" choice from the outset. So to that end I will be trying each major Distributed VCS, and looking at the associated packaging helpers to decide on which to use. If you have any insight or opinions on this, please leave a comment or mail me.

Frans Pop reported recently that the initramfs did not fit in the flash of the QNAP TS-109 when you used LVM. We had problems with initramfs images that were too large before (on the NSLU2). By default, initramfs-tools uses the MODULES=most setting which puts all modules that might be of interest to booting a machine in the initramfs. This is a good idea on a PC where the hardware can change a lot, but it makes less sense on most NAS devices. Frans has now changed debian-installer so the MODULES policy can be chosen during the installation. His change allowed architecture specific defaults, so I've changed ARM to use MODULES=dep. debian-installer will now create the file /etc/initramfs-tools/conf.d/driver-policy with a MODULES setting that will override that from /etc/initramfs-tools/initramfs.conf. On QNAP devices, I intend to only support MODULES=dep installations, so please change your configuration if you've installed Debian already. On the NSLU2, MODULES=most will of course continue to be supported.

So it looks like the project I’ve been laboring on has been getting some attention:

Ever thought it was difficult to write software for Linux? For multiple distros? InternetNews reports that the LSB is making a push for their next release (due out later this year) that should help make all that much easier.

They even link to our project status page. Cool! Of course, good publicity invites criticism. This time, there seem to be two themes. William Pitcock seems to have the most succinct summary:

To put things simply, the LSB sucks. Here s why:

• The LSB spec depends on RPM. I mean, come on. Seriously. Why do they need to require a specific package manager? If package handling is really required, then why not create a simple package format that can be converted on demand into the system package format? Or why care about packages at all?
• The LSB spec invents things without consulting distros. Like the whole init scripts thing. But that s not as bad as depending on RPM or requiring a specific layout.

(See also Scott James Remnant.) Let’s take this one part at a time. Today’s topic: packaging. Part of William’s problem may be that he doesn’t understand the spec. The LSB doesn’t require a specific package manager, or a specific package format. It doesn’t even require that the distribution be set up using package management at all! The spec only requires that LSB-compliant software be distributed so that any LSB-compliant distribution can install it. That could be tarballs with POSIX-compliant install scripts, an LSB-compliant install binary, a shar archive, a Python script with embedded base64 binaries, whatever. One of the options allowed is an RPM package, with a number of restrictions. The restrictions are key, because they effectively define a subset of RPM that acts as, to quote William again:

…a simple package format that can be converted on demand into the system package format…

The difference being, of course, that we didn’t reinvent the wheel and create our own; we used a popular format as the basis for ours. Scott raises another concern:

While much of the LSB can be hacked into a different distribution through compatibility layers and tools, such as alien, what ISV or other vendor wants to provide a support contract against a distribution that has such kludges?

I’m not sure if he’s referring specifically to packaging or to the standard in general. As regards packaging: the reason we specify a strict subset is because we can test that subset, and we’ve tailored it to the needs of tools such as alien. The theory goes that alien isn’t a kludge when it comes to LSB packages. But, as already mentioned, if vendors aren’t comfortable with supporting RPM, they have a number of other options. As it turns out, most of them are doing just that; the feedback we’re getting from most ISVs is that packaging (whether LSB-subset RPM, full RPM, or Debian) is just not worth the effort. Coming up: part 2…

It s certainly funny to read articles about the future, but it s even funnier to read past articles about now. I ve just found an article written in 1968 about how thing would be 40 years in the future (or today). Of all the foreseen things, I would really like to see domed cities. Although I don t think any real goal would be achieved by it, surely it s quite a sight. Also more free time for leisure wouldn t hurt

Probably still affected by jetlag, I've decided at the end of last week while going through my Debian mailinglists backlog, to (try to) fix one RC bug per week from now on until Lenny is released. I guess I was also influenced by Neils talk about Lenny at DebConf8 :-) At that time, which it is merely nine days ago, there were 378 RC bugs open in Lenny. Today we have 428 :-(

Also I decided I will blog about this regulary, in the hope that others pick up similar procedures for them, so that we can release Lenny sometime soon. We, as a project, need to gain speed in fixing these issues, this will only happen if more people start fixing these bugs. After that, we can happily go back to adding more features! ;-)

So for now I closed (or contributed to closing) three bugs: #492299: downgraded & closed, generic bug report, users didnt provide moreinfo, #495587 (bug in atd, caused by a bug in lsb-base, suggested to forcemerge), #438885 (downgraded, as all blocking bugs for this one have been fixed).

For 475036 (removal of kernel-package requested by maintainer) I updated status in the bugreport and notified the kernel-team, that they are one of the two last users of this package in Debian. Not sure which change is more appropriate now: fix kernel-package, so that it can stay in Lenny, or change the linux-2.6 build-system.

The other package which uses kernel-package is cdfs-src, but I'm not sure we should with that package anyway, see 482075.

That's it for this week. Oh, I forgot to mention why I choose one RC bug per week: it's a goal I can fullfill. If I'd choose more, I might not manage to keep up with my plan and stop it altogether. So I choose something which I hopefully can manage over a some period of time ;-) I'm aware this is not very much, but at least something.

What's your plan to help releasing Lenny on time?

In a comment on my AppArmor is dead post [1] someone complained that SE Linux is not “Unixish“. The security model in Unix is almost exclusively Discretionary Access Control (DAC) [2]. This means that any process that owns a resource can grant access to the resource to other processes without restriction. For example a user can run “chmod 777 ~” and grant every other user on the system the ability to access their files (and take over their account by modifying ~/.login and similar files). I say that it’s almost exclusively DAC because there are some things that a user can not give away, for example they can not permit a program running under a different non-root UID to ptrace their processes. But for file and directory access it’s entirely discretionary. SE Linux is based around the concept of Mandatory Access Control (MAC) [3]. This means that the system security policy (as defined by the people who developed the distribution and the local sysadmin) can not be overridden by the user. When a daemon is prevented from accessing files in a user’s home directory by the SE Linux policy and the user is not running in the unconfined_t domain there is no possibility of them granting access. SE Linux has separate measures for protecting integrity and confidentiality. An option is to use MultiLevel Security (MLS) [4], but a more user-friendly option is MCS (Multi-Category Security). The design of SE Linux is based on the concept of having as much of the security policy as possible being loaded at boot time. The design of the Unix permissions model was based on the concept of using the minimal amount of memory at a time when 1M of RAM was a big machine. An access control policy is comprised of two parts, file labels (which is UID, GID, permissions, and maybe ACLs for Unix access controls and a “security context” for SE Linux) and a policy which determines how those file labels are used. The policy in the Unix system is compiled into the kernel and is essentially impossible to change. The SE Linux policy is loaded at boot time, and the most extreme changes to the policy will at most require a reboot. The policy language used for SE Linux is based on the concept of deny by default (everything that is not specifically permitted is denied) and access controls apply to all operations. The Unix access control is mostly permissive and many operations (such as seeing more privileged processes in the output of “ps”) can not be denied on a standard Unix system. So it seems that in many ways SE Linux is not “Unixish”, and it seems to me that any system which makes a Unix system reasonably secure could also be considered to be “not Unixish”. Unix just wasn’t designed for security, not that it is bad by the standards of modern server and desktop OSs. Of course many of the compromises in the design of Unix (such as having all login sessions recorded in a single /var/run/utmp file and having all user accounts stored in a single /etc/passwd file) impact SE Linux systems. But some of them can be worked around, and others will be fixed eventually.

• [1] http://etbe.coker.com.au/2008/08/23/apparmor-is-dead/


• [2] http://en.wikipedia.org/wiki/Discretionary_Access_Control


• [3] http://en.wikipedia.org/wiki/Mandatory_access_control


• [4] http://en.wikipedia.org/wiki/Multilevel_security

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The Linux kernel has a number of code sections which look at the apparent size of the machine and determine what would be the best size for buffers. For physical hardware this makes sense as the hardware doesn’t change at runtime. There are many situations where performance can be improved by using more memory for buffers, enabling large buffers for those situations when the machine has a lot of memory makes it convenient for the sysadmin. Virtual machines change things as the memory available to the kernel may change at run-time. For Xen the most common case is the Dom0 automatically shrinking when memory is taken by a DomU - but it also supports removing memory from a DomU via the xm mem-set command (the use of xm mem-set seems very rare). Now a server that is purchased for the purpose of running Xen will have a moderate amount of RAM. In recent times the smallest machine I’ve seen purchased for running Xen had 4G of RAM - and it has spare DIMM slots for another 4G if necessary. While a non-virtual server with 8G of RAM would be an unusually powerful machine dedicated for some demanding application, a Xen server with 8G or 16G of RAM is not excessively big, it’s merely got space for more DomU’s. For example one of my Xen servers has 8 CPU cores, 8G of RAM, and 14 DomUs. Each DomU has on average just over half a gig of RAM and half of a CPU core - not particularly big. In a default configuration the Dom0 will start by using all the RAM in the machine, which in this case meant that the buffer sizes were appropriate for a machine with 8G of RAM. Then as DomUs are started memory is removed from the Dom0 and these buffers become a problem. This ended up forcing a reboot of the machine by preventing Xen virtual network access to most of the DomUs. I was seeing many messages in the Dom0 kernel message log such as “xen_net: Memory squeeze in netback driver” and most DomUs were inaccessible from the Internet (I didn’t verify that all DomUs were partially or fully unavailable or test the back-end network as I was in a hurry to shut it down and reboot before too many customers complained). The solution to this is to have the Dom0 start by using a small amount of RAM. To do this I edited the GRUB configuration file and put “dom0_mem=256000” at the end of the Xen kernel line (that is the line starting with “kernel /xen.gz“). This gives the Dom0 kernel just under 256M of RAM from when it is first loaded and prevents allocation of bad buffer sizes, it’s the only solution to this network problem that a quick Google search (the kind you do when trying to fix a serious outage before your client notices (*)) could find. One thing to note is that my belief that it’s kernel buffer sizes that are at the root cause of this problem is based on my knowledge of how some of the buffers are allocated plus an observation of the symptoms. I don’t have a test machine with anything near 8G of RAM so I really can’t do anything more to track this down. There is another benefit to limiting the Dom0 memory, I have found that on smaller machines it’s impossible to reduce the Dom0 memory below a certain limit at run-time. In the past I’ve had problems in reducing the memory of a Dom0 below about 250M, while such a reduction is hardly desirable on a machine with 8G of RAM, when running an old P3 machine with 512M of RAM there are serious benefits to making Dom0 smaller than that. As a general rule I recommend having a limit on the memory of the Dom0 on all Xen servers. If you use the model of having no services running on the Dom0 there is no benefit in having much ram assigned to it. (*) Hiding problems from a client is a bad idea and is not something I recommend. But being able to fix a problem and then tell the client that it’s already fixed is much better than having them call you when you don’t know how long the fix will take.

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Polysms Here is my first software designed for the FreeRunner: polysms. It's a commandline tool: you pass it a polygen grammar name and a phone number, and it will send a SMS to that phone number using the polygen output for that grammar as the SMS text:

# polyrun manager 0012345678

And here is the code, that works on the http://www.freesmartphone.org dbus framework:

I took a note of the various talks I attended at DebConf, with the aim of writing a few notes about each so that I could try to explain to my work mates exactly what I get out of going. However I think a lot of the benefit is about general face to face contact with fellow DDs and random conversations that happen. Having worked from home for over 3 years I'm finding it quite nice to be back in an office with people working on the same things as me; there are conversations that you will have over a quick cup of coffee or in the corridor that you wouldn't bother typing on IRC or email or picking up the phone for. Debian is a lot like a large organisation full of telecommuters and DebConf provides a vital opportunity for us to have those "minor" conversations that prove quite useful and to remind each other what we're actually like in person. I didn't end up writing a lot of notes during the talks so these are just snippets after the fact. If I'd been more organised I'd have done a write up on a daily basis rather than leaving it all until the week after. A lot of the below is fragmented thoughts, but the longer I leave it the less relevant it gets and the more chance I forget something. It'd have been up faster if I hadn't been fighting Movable Type to try and get some sort of headings. Sunday
Introduction, Marga The "Welcome to DebConf" bit. Marga got up and talked about how at DebConf4 (Brazil) she hadn't been a DD and now she was and how it had been a life changing event. She'd thought she was to blame for DebConf8 in Argentina, but trawling mail archives had shown it was originally Mart n's idea. She hadn't realised at the start quite how much work it would be. Steve's DPL talk, Steve McIntyre The DPL welcomes us to DebConf and talks about Debian's achievements, some of the results of his team survey (the teams largely say they need more manpower. Not really a huge surprise.). NM/User Survey BOF, Paul Wise Paul emailed debian-user, debian-newmaint and various other places (I think) asking about people's experiences as a Debian user or applicant to New Maint. His final results aren't yet published and I got the impression a disappointing number of our users had replied. The NM problems these days seem to be largely down to a lack of AMs, at least according to the stats on nm.debian.org. Meet SPI board - bdale, maulkin, jimmy, michael, others A chance to meet those of the SPI board who were present. The usual "If you're involved with Debian you should seriously consider joining SPI". Some discussion about the fact that although SPI was originally mostly Debian these days other projects are making more and more use of it - OFTC, PostgreSQL and Madwifi for example. Not a huge amount of new information for me. I've been an SPI member for some time and I think they perform a vital role for Debian. They've had issues in the past but it's really good to see them overcome and more projects on board. Monday
http://hp.com/go/debian, bdale Bdale talks about the history of Debian and HP. And makes the point that HP aren't doing any of this to be "nice"; their primary responsibility is to their shareholders. Not surprising, but it's good that even with that criteria at the fore front Debian ends up a good idea for a large multinational. Managing 666 packages, Mart n Ferrari Mostly centered around the pkg-perl experience and the tools/workflow they have to help manage things. Impressive web tool (DEHS) to help track packages with new upstreams, issues or pending uploads. Quality Assurance in Lenny + 1 I can't remember a lot of this, which is a bit bad. I remember a discussion about whether we should release with orphaned packages, or if they should be removed. The argument for not removing them seemed to revolve around a theory that if they weren't buggy then what was the harm, the argument for was that if they were unmaintained and not really used than how did we actually know they weren't buggy, and was it reasonable that they potentially held up library transitions etc? Bugs in large packages Don Armstrong and ways in which the BTS can help people with lots of bugs. This (thankfully) doesn't affect me, but it was interesting to hear Don talk about his work on the BTS and his various ideas. I was sorry I'd missed his talk on SOAP access to it; I shall have to find time to watch the video. Tuesday
Debian and Ubuntu, Mark Shuttleworth The usual interaction with Debian stuff, including how we interact with our upstreams. If a bug is raised with an Ubuntu package then it might well be appropriate to raise it with Debian and upstream as well, but each set of people should be able to use their own bug reporting systems rather than having to go to a foreign system. I don't think it was actually said, but I guess the idea is that launchpad is the thing that will do this gluing together. He also talked about Ubuntu as an "experiment" rather than a fork of Debian; something that has potentially different ideas about how to do things but that these ideas may lead to things that should be fed back into Debian. The point was made that even if you consider Ubuntu a fork they've forked 9 times now; it hasn't been a case of forking once and diverging wildly since thast point. I have a few thoughts on all the whole Debian/Ubuntu stuff which I should really try to form into something coherant and post. I think it's important to take Mark's talk in the context of bdale's "Shareholders come first" point. Derivatives round table Didn't stay for most of this. Ubuntu, Debian-EDU (which I hadn't realised was a derivative rather than a team within Debian, but apparently there are various things it was much easier for them just to patch now and try to work towards a generic solution later), someone from Extramadura and someone from the Munich government Linux stuff. I'm sure I've missed someone off. tdebs/i18n This was a useful BOF. It helped that we said no to the usual video team requirement that if you want to speak you had to wait for the microphone. This works fine for a normal talk, but really impedes the flow of conversation in something like a BOF. tdebs are something that have partly come from a need of Emdebian to reduce installed package size and partly from the desire of the i18n team to be able to update package translations without having to do a full binary NMU of a package. We had some of the FTP team, the release team, the i18n team and Emdebian there and I think some progress has been made. There'd been various conversations had before this meeting which I think helped people think about the issues and objections so that we had answers by the time we all sat down together - an excellent example of the use of DebConf. DebConf9 C ceres Various bits of discussion about next year's DebConf in Extramadura. Temperature is likely to be an issue for me as they reckon it could easily get up to 40C! I'll melt! Venue sounds good; some queries regarding late night hacklabs and net connections to same, but I'm sure the networking team will sort it all out as usual. ;) DebConf10 bids Venezela and New York were both pitching. Lots of people don't want to travel to the US or think they'll have problems doing so (I hadn't realised there was such an issue for people from South America). I suspect various people will have issues with Venezela as well; I heard expressions of doubt over their political stability expressed. However I'd be happy to go to either (and preferably both! DebConf10 + 12 perhaps?) Speaking of which, what ever happened to the Sarajevo bid? If they're reading, have you considered DebConf11? Wednesday
A day trip to an Argentinian ranch and lunch was an asido. Fantastic food and a pleasant afternoon spent sitting in the sun chatting to people. That evening was the formal, but thanks to having stayed up until after 4 on Tuesday I had to wimp out and go to bed fairly early. Not until I'd seen the DPL dance though. :) Thursday
Internationalization in Debian I forget most of this other than pretty graphs from Christian regarding what's translated and what other languages we might have; e.g. you can consider South America to be covered largely by Spanish and Portuguese, or you can consider it to not be covered very much at all by the local indigenous languages. dh-make-webapp: yeah right! Mainly what I took away from this was "It'll never happen thanks to the fact that every web app author uses a different system" and that more work needs to be done on the web apps best practices document. I don't really do web apps, but having them easily installable on my systems is a good thing so I hope some standardisation within Debian comes from this. Best practises in team-maintaining packages Various team members got up to talk about work flow in their teams. Not unsurprisingly different things seem to work for different people. Predictable PRNG in the Vulnerable Debian OpenSSL Package Lucian giving his Black Hat talk about the OpenSSL issues we faced earlier this year. Some queries about automated testing and that it should have found this, which originally I agreed with until I thought about it - you'd have to have run > 65536 tests and compared all the data to find this; something like the FIPS tests against a single run wouldn't have shown any issues. Lucian wanted feedback on ensuring he was presenting the Debian side of things acceptably as well. Keysigning Run by Don Armstrong. Nothing to really remark except I think key signing attendance is dropping off after things like the Helsinki experience. Also I've now managed to get my new RSA key signed by keys other than my own (and I'll try to get sorted out to sign keys myself soon). Friday
LessWatts Intel's drive towards reducing power usage. Odd to hear such things from someone who wasn't Matthew Garrett and I think I'd heard most of it before. Debian technical policy update Sorry Manoj, I should have been paying more attention. Debian Policy is something I think is important, but I'm not enough of a nitpicker to really feel I can contribute a whole lot. Virtualisation in Debian - Present and future This was depressing. What I took away was "We had 2 forms of virtualisation in etch (Xen + vserver) and we're supporting neither for Lenny". As someone running a Xen machine this is problematic. The host does have the hardware support that would allow kvm, but I'm worried about smooth migration (it's a colo box). There was some mention of Xenner, which isn't packaged for Debian. I took a look at doing so but there are some worrying items in the TODO list (like, oh, locking to enable reliable SMP) and I've spectacularly failed to get it compiling so far. I should have another go. Emdebian update Neil Williams about where Emdebian is and waved his Balloon3 about. Some interest from the Openmoko guys and discussion about why it might be better than OpenEmbedded. And equally what it couldn't do that OpenEmbedded can manage (mainly very small installs; a minimal Emdebian install is 24MB+ and with X that goes up to 75MB+ I believe). netconf I'd never actually seen Martin talk about netconf before. Am impressive flow of control diagram. It all sounds quite complex for little benefit at present, but if he pulls it off then I can see it being a much more flexible replacement for the likes of Network Manager. Saturday
Lenny - The Road To Release Neil played with putting the heads of the release team on random images. And tried to tell us all how to behave during the release process in terms of what should and shouldn't be uploaded etc. Most of it is just common sense, but apparently everything he talked about he'd experienced. Also pointed out we were supposed to release in 3 weeks and didn't even have the appropriate kernel in testing yet so it's probably not going to happen. Colour me surprised. Sustainable Computing Low power consumption/affordable computing. Interesting points about the OLPC being used in the middle of nowhere with no chance of an Internet connection being close by compared to neighbours in large cities where people can't necessarily afford top of the line computers or individual connections - in this sort of scenario mesh networking is really viable in terms of getting people connected up. Multi winner voting Manoj needs pretty diagrams, probably drawn by Martin Krafft. ;) Semi-interesting discussion about multi-winner voting (e.g. SPI board elections) and how the current Debian voting system is completely tied to Debian's infrastructure eg the LDAP setup. Manoj would like to make it more generic so it could be used by other groups as well as for different sorts of votes in Debian.

I recently wrote about wanting to have a teletype. Well, I have since realized that teletypes weigh hundreds of pounds, draw hundreds of watts, and aren't available on eBay for a reasonable price. Well I knew the hundreds of pounds bit, but still. I pretty well have had to give up on a real teletype.

So, now on to the next best thing: a teletype simulator. Enter the two free dot-matrix printers that found their way to my office earlier this week. One of them even works. I bicycled to the awesome local office supplies store (about 11 miles away) to buy a ribbon for it. This is the place that's been there since the 1890s. They still stock dot matrix ribbons, typewriter ribbons, and even fanfold paper.

On the project. Linux has its heritage in Unix, which was used with these devices. It can be made to work with them even now. But there's a trick: teletypes used a bidirectional serial link. Dot matrix printers have no keyboard. So we have to take input from a different device than we send output to.

A simple trick will do for that:

TERM=escpterm telnet localhost > /dev/lp0

Now, here's the next problem. Dot-matrix printers have a line buffer. They don't start printing the line at all until they see CR or LF. Makes it annoying for interactive use. So I wrote a quick tool to insert into that pipeline. After a certain timeout after the input stops, it will force the printer to flush its buffer. Took a little while to figure out how to do that, too; turns out there's a command ESC J that takes an increment for vertical spacing in 1/216 inch, and accepts 0. So I can send \x1BJ\x00 to flush the buffer. I can run it like this:

TERM=escpterm telnet localhost escpbuf > /dev/lp0

That leaves another problem, though: the printhead is right over the text. (Even though it moves to the right of the printing position, and then moves back left for the next character to print.) I modified the program to roll the paper out a bit, and then reverse feed it to continue printing the line. But that is slow and, I suspect, tough on the stepper motor.

Also, I have crafted a terminfo file for the Epson-compatible dot-matrix printers (which are almost all of them), which can also be found at the above link.

So here's the question, for anyone that has used a real teletype:

Did the printhead obscure the text there too, or could you see the entire current line at all times?

From the 13th to the 14th of August my Play Machine [1] was offline. There was a power failure for a few seconds and the machine didn’t boot correctly. As I had a lot of work to do I left it offline for a day before fixing it. The reason it didn’t boot was that due to an issue with the GRUB package it was trying to boot a non-Xen kernel with Xen, this would cause the Xen Dom0 load to abort and it would then reboot after 5 seconds - and automatically repeat the process. The problem is that update-grub in Lenny will generate boot entries for Xen kernels to boot without Xen and for non-Xen kernels to boot with Xen. Two days ago someone launched a DOS attack on my Play Machine and I’ve only just put it back online. I’ve changed the ulimit settings a bit, that won’t make DOS attacks impossible, just force the attacker to use a little bit more effort.

• [1] http://www.coker.com.au/selinux/play.html

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