I got several emails in reply to my previous post on representing Sudoku problems as package dependencies. Several people asked about the algorithm that aptitude uses to solve these problems. A slightly out-of-date discussion package management and the aptitude algorithm can be found at http://people.debian.org/~dburrows/model.pdf. One question was interesting enough to deserve a follow-up blog post: Wolf T. referred to the page http://norvig.com/sudoku.html and asked how long it would take aptitude aptitude to solve the hard Sudoku problems on that page. He suspected that aptitude would do basic constraint propagation and then be forced to exhaustively search all the possible solutions to the problem. In brief: the answer is that it doesn't work by default, but not for the reason he suggested, and you can make it work with a few command-line arguments. In order to try this out you'll need a new version of the Sudoku reducer that can parse the problems on that Web page: debsudoku2.py. If I do a straight conversion of one of those problems and then run it through aptitude, it goes spinning off and never comes back. But aptitude is coded to avoid exhaustive searches; otherwise it couldn't solve dependency problems in reasonable amounts of time. In this particular situation, though, aptitude is clearly performing an exhaustive search; here's one series of status outputs:

open: 5124; closed: 4993; defer: 0; conflict: 374
Resolving dependencies...
open: 10090; closed: 9942; defer: 0; conflict: 398
Resolving dependencies...
open: 14726; closed: 14888; defer: 0; conflict: 440
Resolving dependencies...

Here open is the number of partial solutions that aptitude wants to examine, and closed is the number that it's already examined. aptitude isn't making progress here and it isn't finding solutions; in fact, it's creating, on average, about two new partial solutions for every one it examines. Why is aptitude doing this? Its resolver isn't a brute-force algorithm; in fact, it looks remarkably like the Sudoku solver discussed at http://norvig.com/sudoku.html. On each step, aptitude takes a partial solution, picks one dependency, and resolves it by installing or removing a package. This is pretty much equivalent to filling in one not-filled-in cell; in fact, in the conflicts Sudoku reduction, it's exactly equivalent. There is one difference, though, and it stems from a difference in the problem domains of Sudoku and package management:

Not all dependency resolutions are created equal.

In Sudoku, any solution to the puzzle will do. Not so in package management; solving a dependency problem by removing every package on the system will produce a formally correct answer and a very unhappy user. Even results that are not utterly disastrous could be annoying to the user, so the resolver needs to somehow aim for good answers. The page on Sudoku solvers suggests sticking to whatever value you placed in a cell, unless that doesn't lead to any solutions at all. This is technically known as a depth-first search. The problem with taking this approach when resolving package dependencies is that an apparently safe choice can end up requiring undesirable actions later on (like removing large swathes of the system). For this reason, aptitude tries to strike a balance between sticking to its current line of reasoning, and abandoning it when it seems to be turning out badly (this makes it a form of best-first search). On typical Debian archives, the package relationships are simple enough that it's OK if aptitude does this from time to time; it makes the search a little more thorough (thus costly), but the ability to back out of questionable branches is very valuable. But it looks like when aptitude is applied to Sudoku puzzles, it has trouble settling on a single series of choices. It keeps thinking that the solutions are getting worse, so it backs up and tries another branch, but they don't look any better over there, so it backs up and tries another branch, and so on. The option Aptitude::ProblemResolver::StepScore sets how hard aptitude will try to stick to the same line of reasoning. Its default value is 70, which is reasonable for package archives, but turning it up to a large value such as 10000 will cause aptitude to use a straight depth-first search, just like the Sudoku page recommends:

$ aptitude -s -o 'aptitude::problemresolver::stepscore=10000' -o 'aptitude::auto-install=false' install puzzle

Setting auto-install to false is a workaround for another odd corner case/bug that happens to bite this Sudoku problem: for technical reasons, doing this lets aptitude know that it should avoid solutions that cancel the installation of puzzle. Otherwise you have to sit there telling it no for a bunch of solutions you aren't interested in. Future versions of aptitude will probably provide a way to explicitly give hints to the resolver. With these options, aptitude was able to solve the hard Sudoku puzzles that I gave it in anywhere from fifteen seconds to a minute and 47 seconds. In contrast, the straight Sudoku solver does 30 problems in a second. Why is aptitude so slow? Based on skimming debug traces and looking at the run-time behavior, I conjecture that there are several reasons:

1. The aptitude search algorithm is very heavyweight. In the case where it takes over a minute, it only actually examines about 5,000 possible solutions. I don't know exactly where all this time is going, but I do know that the resolver does a lot of work on each step, for instance to try and detect dead ends that it hasn't reached yet. This is the conflicts counter that appears while the resolver is running. This pays off tremendously in terms of allowing aptitude to skip huge amounts of work (it may be why aptitude can solve Sudoku puzzles at all!), but it means that the resolver takes a long time for each potential solution it looks at.
2. The Sudoku page suggests taking the cell with the fewest number of possible entries as the choice. I distinctly remember writing code to do this in aptitude, but it looks like I threw it out at some point or never committed it. I don't see why it should be any worse than the current approach, though (which is to pick an arbitrary dependency); maybe it just got misplaced at some point. Implementing this behavior decreased the time required to solve one puzzle from a minute and 45 seconds to just under a minute; I've committed this change to the post-lenny branch.
3. The Sudoku resolver has the advantage of being able to very quickly identify illegal moves. aptitude's resolver can learn this information, but it takes time and it can't apply Sudoku-specific optimizations. For instance, the Sudoku solver knows exactly which values can be placed in a given cell at any time. aptitude has to actually consider each of the cells that's available as a possibility and prove to itself that, e.g., 4 and 6 can't be written in the same cell at the same time. And although it can learn this information, it takes time to do so and it takes time to see whether any of the past conflicts that it remembers are present in a given solution.

As I noted above, I've already checked in one change to the resolver's behavior. It might also be worth seeing what happens with a massive increase in StepScore, so I've pegged it at 10000 on my computer to see whether the results I get are noticeably worse. The third item above -- the fact that aptitude needs to do more work to understand which packages can't be installed -- is interesting. The Sudoku solver is very proactive about this: it keeps track at all times of which cell values are legal, and updates these sets every time it transitions. In contrast, aptitude constantly re-checks all the possible moves it could make to see which ones are currently legal. I think that the resolver's speed could be boosted a little by doing the following:

1. Cache the currently legal solutions of each dependency at the time it's inserted into the queue.
2. When a new search node is generated by resolving a dependency, drop the formerly legal moves that are knocked out (for instance, by installing a different version of the same package).
3. Come up with a quick way of re-testing new conflicts (the global list of dead-ends) so that search nodes that are already in the queue can be checked against the conflicts that were added since they were queued.

These changes won't make aptitude able to solve problems that it couldn't solve before, or at least not very many of them, but they should make the resolver faster on every problem it encounters. However, I don't think I want to actually implement them. It would be tricky to confirm that the resolver got faster on real dependency problems (since it's normally almost instantaneous), the changes would make the resolver code more complex and fragile (less readable, less maintainable), and there's a real chance of breaking something. Unless there are cases where the resolver is currently too slow on real package archives that don't involve an exponential blowup, I'm going to shelve the idea for now.

All "low quality" videos (which in fact have better quality than the streams had) from DebConf8 are now available for download at the usual location. Enjoy!

I expect the rest of the high quality ones to appear during the next 48h, after that I'll start with the remaining post processing, which will take a bit longer, probably some weeks, hopefully only a few though :-)

Currently there are 57 events available in low quality (4,9G in size) and 30 in high (14G). The SPI event is the only one I know that is missing, but I still need to check if we have it on tape and if there are more missing.

If you notice any non-obvious problems with these videos, please don't tell me, but do describe the problem in our todo list. Thanks!

To make that a bit more clear: There is only one kind of obvious problem: more than one file per event. It's obvious that these need to be merged. All other issues, like a completly missing event, missing beginning of an event, or silence instead of audio, etc. should be noted in our todo-list. Your help here is very much appreciated.

Been busy with things, and for fun I will tell you about it using three song titles:

#1 "... Baby One More Time"

#2 "Don't Worry, Be Happy"

#3 "Je reviens Montr al"

Time to stock up on sleep.

Sick of a ridiculous pile of tiny bottles falling everywhere in your cupboard? Many people will sell you many expensive solutions. However, I think we've hit on something cheap, effective and practical; zip-lock bags in a deep tub, labelled with sticky tags.  

• Easy to find.
• Easy to get any sized spoon into the bags, or for tipping if you just open a corner.
• For freshness, you can vaccuum seal with a straw a-la Alton Brown.
• Buy the cheap spices in bulk and pay significantly less.
• The more expensive bags with two rows of sealing are a little easier to close, if they come in a good size for your container.
• Label with the date if you know it.

For some time there have been two mainstream Mandatory Access Control (MAC) [1] systems for Linux. SE Linux [2] and AppArmor [3]. In late 2007 Novell laid off almost all the developers of AppArmor [4] with the aim of having the community do all the coding. Crispin Cowan (the founder and leader of the AppArmor project) was later hired by Microsoft, which probably killed the chances for ongoing community development [5]. Crispin has an MSDN blog, but with only one post so far (describing UAC) [6], hopefully he will start blogging more prolifically in future. Now SUSE is including SE Linux support in OpenSUSE 11.1 [7]. They say that they will not ship policies and SE Linux specific tools such as “checkpolicy”, but instead they will be available from “repositories”. Maybe this is some strange SUSE thing, but for most Linux users when something is in a “repository” then it’s shipped as part of the distribution. The SUSE announcement also included the line “This is particularly important for organizations that have already standardized on SELinux, but could not even test-drive SUSE Linux Enterprise before without major work and changes“. The next step will be to make SE Linux the default and AppArmor the one that exists in a repository, and the step after that will be to remove AppArmor. In a way it’s a pity that AppArmor is going away so quickly. The lack of competition is not good for the market, and homogenity isn’t good for security. But OTOH this means more resources will be available for SE Linux development which will be a good thing.

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


• [2] http://www.nsa.gov/selinux/


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


• [4] http://news.cnet.com/8301-13580_3-9796140-39.html


• [5] http://blogs.msdn.com/michael_howard/archive/2008/01/17/crispin-cowan-joins-the-windows-security-team.aspx


• [6] http://blogs.msdn.com/crispincowan/default.aspx


• [7] http://news.opensuse.org/2008/08/20/opensuse-to-add-selinux-basic-enablement-in-111/

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Here in Dublin I’ve been more “formally” introduced to the world of board games. Back at home, a friend had a copy of Settlers of Catan, and we used to play every now and then, but that was it. Since I arrived I’ve been attending to weekly “board game nights”, and I’ve had the opportunity to play several more, most of which I liked a lot. I’ve played Agricola, Caylus, and Power Grid, all very nice. I’ve also played Race for the Galaxy, which I didn’t like much at first, but which I’ve come to enjoy a bit more as of lately. (All four are in the top-10 of Board Game Geek.) I’m going to miss this when I get back, particularly since my friends will most certainly not be up to weekly games. I should investigate to see if some kind of board games club exists in Alicante. If you know of one, or are reading this and would be interested in organizing something, please let me know.

Apparently the LUG’s website is still off-line and there’s no idea when it will return, so let me use this site to help announce that the LUG’s regular meeting at the Knights Templar public house, near Isambard Walk, Bristol, will happen tomorrow Saturday 23 August from noon-ish until whenever people drift away. Software Freedom Day happens between this meeting and the next one. Is anyone interested in running a Bristol-area event and do you know of a suitable/available venue? I’m finding the SFD official site somewhat dysfunctional (I’m not in the Northern Caucasus, damnit), so I’ve not found a nearby team registered yet…

Docking the FreeRunner into the laptop Earlier in the day, I wrote:

So yes, my laptop can now be turned into a phone charger with networking, DNS and apt cache services. I shall look into hooking that script into dbus to have it run automatically when the phone is plugged and unplugged.

It's not dbus, it's udev, and I've managed to do it. It's an udev rule:

# cat /etc/udev/rules.d/z60_openmoko_net.rules
ACTION=="add", SUBSYSTEM=="net", ATTRS idVendor =="1457", ATTRS idProduct =="5122", RUN+="/root/bin/share-openmoko"
ACTION=="remove", SUBSYSTEM=="net", INTERFACE="usb0", RUN+="/root/bin/share-openmoko"

And a script:

# cat bin/share-openmoko 
#!/bin/sh
if [ "$ACTION" == "add" ]
then
    ACTION=start
fi
if [ "$ACTION" == "remove" ]
then
    ACTION=stop
fi
INTERFACE=$ INTERFACE:-"usb0" 
ACTION=$ ACTION:-"$1" 
case "$ACTION" in
    start)
        logger -t openmoko "Connected, setting up network"
        iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE -s 192.168.0.200/29
        ifconfig usb0 192.168.0.200 netmask 255.255.255.248
        /etc/init.d/dnsmasq start
        echo 1 > /proc/sys/net/ipv4/ip_forward
        ;;
    stop)
        logger -t openmoko "Disconnected, bringing down network"
        echo 0 > /proc/sys/net/ipv4/ip_forward
        /etc/init.d/dnsmasq stop
        iptables -t nat -F POSTROUTING
        ifconfig usb0 down
        ;;
esac

The script has extra cruft that makes it double as a udev script and as a init.d style script, just because I didn't feel like abandoning the init.d style interface. However, udev handles it perfectly, so there's probably no use at all for the start/stop part. This means that the interface and all supporting services will be brought up and down when the phone is connected/disconnected, and also when the phone is suspended/resumed. Of course, more fancy things can be plugged into the script, like syncing PIM info, file systems, turning on applets in panels, mounting phone file systems and whatnot.

Unpacking the new FreeRunner I got myself a FreeRunner. Here are some notes from the first few days: Available operating systems The FreeRunner comes with the Om 2007.2 distribution: it works for basic phone things, and it has an opkg package manager that you can use to install all sort of extra software. Only issue: the SMS application was rather unstable with my SIM card. I then tried Om 2008.8, which is a major new redesign, partly based on Qtopia. It's definitely more advanced on how it looks, with smooth animations all around, but I did not manage to get the GSM part to work, because I did not manage to get it to ask for a PIN. I then tried plain Qtopia and I got what looks and feels like a properly working mobile phone. The only issue that it has is that I did not manage to make it suspend, so battery life is much shorter than it could be. Apparently, this should improve as kernel 2.6.26 reaches the phone. I kept Qtopia installed in the phone flash as a "stable" phone system. And finally, Debian. Debian is based on the freesmartphone.org software stack, which is an attempt to create a UI agnostic DBUS frontend to the hardware that supports multiple applications running on top of it. It is a young project, but it can already drive a mobile phone in a useful way. It has a demo interface that is basically a showcase of what is implemented in the DBUS frontend, but does most of the basic things you need from a mobile phone, including taking and making phone calls. And then it has Debian behind, all of it. I need to buy a bigger microsd card. Tips and tricks Flashing things

1. apt-get install dfu-util
2. Start the Freerunner bios/bootloader, by holding down Power and then pressing AUX (standard bootloader), or by holding down AUX and then pressing Power (factory, unbrickable, read only fail safe bootloader).
3. dfu-util -l shows you a list of devices it can access. If you see more than once, you need to specify in all dfu-util commands which one you want, using -d USBID. In my case, I have to always use dfu-util -d 0x1d50:0x5119
4. To flash the kernel: dfu-util -a kernel -R -D /path/to/uImage
5. To flash the root file system: dfu-util -a rootfs -R -D rootfs_filename.jffs2
6. To flash the bootloader: dfu-util -a u-boot -R -D uboot_filename.bin
7. To flash the u-boot configuration: dfu-util -a u-boot_env -D env.new

You can also download all of these things from the FreeRunner by using -U instead of -D. Networking via USB All of the distributions I tried, by default configure the USB as a gadget with ethernet over usb. You can form a lan with it using the cdc_ether module, and you will find your phone preconfigured as 192.168.0.202 expecting to find a gateway at 192.168.0.200. I made myself this script to start and stop networking with the phone:

#!/bin/sh
case "$1" in
    start)
        iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE -s 192.168.0.200/29
        ifconfig usb0 192.168.0.200 netmask 255.255.255.248
        /etc/init.d/dnsmasq start
        echo 1 > /proc/sys/net/ipv4/ip_forward
        ;;
    stop)
        echo 0 > /proc/sys/net/ipv4/ip_forward
        /etc/init.d/dnsmasq stop
        iptables -t nat -F POSTROUTING
        ifconfig usb0 down
        ;;
esac

Besides doing masquerading, it also brings up dnsmasq so that the phone can always find a DNS together with the router. Another useful trick is to configure the phone to share the approx cache with the laptop:

deb http://192.168.0.200:9999/debian unstable main
deb http://192.168.0.200:9999/debian experimental main
deb http://pkg-fso.alioth.debian.org/debian unstable main

So yes, my laptop can now be turned into a phone charger with networking, DNS and apt cache services. I shall look into hooking that script into dbus to have it run automatically when the phone is plugged and unplugged. Changing the ringtone in Debian In case you don't like the default ringtone, this is how to change it:

1. vi /usr/share/python-support/fso-frameworkd/framework/subsystems/oeventd/receiver.py
2. look for def _play( self ):
3. change the codec in decoder = gst.element_factory_make, if needed. The list of available plugins is on the gstreamer website.
4. change the path in filesrc.set_property
5. /etc/init.d/fso-frameworkd restart and maybe /etc/init.d/zhone-session restart

Yes, the ringtone is currently hardcoded, but it does say it's a prototype after all. Or, if you prefer, it's fully configurable and the configuration can be found in /usr/share/python-support/fso-frameworkd. Configuring the bootloader You can connect to the u-boot bootloader via a serial terminal on /dev/ttyACM0. Type help and you will find that it can do a lot of things. The OpenMoko wiki has pages on the bootloader itself, its commands and the environment. The environment is the configuration of the bootloader, similar somehow to /boot/grub/menu.lst. Unlike grub, you can edit the environment from within the bootloader and then save it using the saveenv command. What I did:

1. A boot entry for Debian, with the kernel on an ext2 partition instead of fat: setenv menu_3 Boot from microSD (FAT+ext2): setenv bootargs \$ bootargs_base rootfstype=ext2 root=/dev/mmcblk0p2 rootdelay=5 \$ mtdparts ro\; mmcinit\; fatload mmc 1 0x32000000 \$ sd_image_name \; bootm 0x32000000
2. Stay in the bootloader until a choice has been made: setenv bootdelay -1
3. Don't power down the bootloader when idle: setenv boot_menu_timeout 99999
4. Always show the menu at boot: setenv stop_in_menu yes
5. saveenv

So now my phone dual boots, and I can choose if I want a more reliable phone now (Qtopia) or if I want to play with my future phone (Debian). Configuring ssh for two host keys on the same host Minor issue, but annoying: since both QTopia and Debian show up on 192.168.0.202, ssh will complain about changed host keys. Here is how to configure ssh to avoid the problem (in ~/.ssh/config):

Host debian
HostName 192.168.0.202
User root
HostKeyAlias debian
Host qtopia
HostName 192.168.0.202
User root
HostKeyAlias qtopia

I’ve just read an amusing series of blog posts about bad wiring [1]. I’ve seen my share of wiring horror in the past. There are some easy ways of minimising wiring problems which seem to never get implemented. The first thing to do is to have switches near computers. Having 48 port switches in a server room and wires going across the building causes mess and is difficult to manage. A desktop machine doesn’t need a dedicated Gig-E (or even 100baseT) connection to the network backbone. Cheap desktop switches installed on desks allow one cable to go to each group of desks (or two cables if you have separate networks for VOIP and data). If you have a large office area then a fast switch in the corner of the room connecting to desktop switches on the desks is a good way to reduce the cabling requirements. The only potential down-side is that some switches are noisy, the switches with big fans can be easily eliminated by a casual examination, but the ones that make whistling sounds from the PSU need to be tested first. The staff at your local electronics store should be very happy to open one item for inspection and plug it in if you are about to purchase a moderate number (they will usually do so even if you are buying a single item). A common objection to this is the perceived lack of reliability of desktop switches. One mitigating factor is that if a spare switch is available the people who work in the area can replace a broken switch. Another is that my observation is that misconfiguration on big expensive switches causes significantly more down-time than hardware failures on cheap switches ever could. A cheap switch that needs to be power-cycled once a month will cause little interruption to work, while a big expensive switch (which can only be configured by the “network experts” - not regular sysadmins such as me) can easily cause an hour of down-time for most of an office during peak hours. Finally the reliability of the cables themselves is also an issue, having two cables running to the local switch in every office can allow an easy replacement to fix a problem - it can be done without involving the IT department (who just make sure that both cables are connected to the switch in the server room). If there is exactly one cable running to each PC from the server room and one of the cables fails then someone’s PC will be offline for a while. In server rooms the typical size of a rack is 42RU (42 Rack Units). If using 1RU servers that means 42 Ethernet cables. A single switch can handle 48 Ethernet ports in a 1RU mount (for the more dense switches), others have 24 ports or less. So a single rack can handle 41 small servers and a switch with 48 ports (two ports to go to the upstream switch and five spare ports). If using 2RU servers a single rack could handle 20 servers and a 24port switch that has two connections to the upstream switch and two spare ports. Also it’s generally desirable to have at least two Ethernet connections to each server (public addresses and private addresses for connecting to databases and management). For 1RU servers you could have two 48 port switches and 40 servers in a rack. For 2RU servers you could have 20 servers and either two 24port switches or one 48port switch that supports VLANs (I prefer two switches - it’s more difficult to mess things up when there are two switches, if one switch fails you can login via the other switch to probe it, and it’s also cheaper). If the majority of Ethernet cables are terminated in the same rack it’s much harder for things to get messed up. Also it’s very important to leave some spare switch ports available as it’s a common occurrence for people to bring laptops into a server room to diagnose problems and you really don’t want them to unplug server A to diagnose a problem with server B… Switches should go in the middle of the rack. While it may look nicer to have the switch at the top or the bottom, that means that the server which is above or below it will have the cables for all the other switches going past it. Ideally the cables would go in neat cable runs at the side of the rack but in my experience they usually end up just dangling in front. If the patch cables are reasonably short and they only dangle across half the servers things won’t get too ugly (this is harm minimisation in server room design). The low end of network requirements is usually the home office. My approach to network design for my home office is quite different, I have no switches! I bought a bunch of dual-port Ethernet cards and now every machine that I own has at least two Ethernet ports (and some have as many as four). My main router and gateway has four ports which allows connections from all parts of my house. Then every desktop machine has at least two ports so that I can connect a laptop in any part of the house. This avoids the energy use of switches (I previously used a 24 port switch that drew 45W [2]), switches of course also make some noise and are an extra point of failure. While switches are more reliable than PCs, as I have to fix any PC that breaks anyway my overall network reliability is increased by not using switches. For connecting the machines in my home I mostly use bridging (only the Internet gateway acts as a router), I have STP enabled on all machines that have any risk of having their ports cross connected but disable it on some desktop machines with two ports (so that I can plug my EeePC in and quickly start work for small tasks).

• [1] http://www.darkroastedblend.com/2008/08/crazy-wiring-part-5.html


• [2] http://doc.coker.com.au/environment/computer-related-power-use/

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This week has been a little hectic, as I've been struggling with testing different versions of the GNU/Linux kernel. Specifically I've been trying to solve a problem where a Phenom processor, when coupled with 8Gb, would kernel panic under heavy load. After testing various patches, kernel versions, and random things I believe the problem is fixed in the kernel version 2.6.27RC4 - however nothing in the changelog appears relevant, so I guess only time will tell. Now we need to solve the problem of Atom processors panicing when attempting to boot 64-bit kernels. That is still present in the 2.6.27RC4 kernel. (ObRandom: If there are any interested parties I can provide remote serial console access to such a system.) Finally I've also been playing with PAM, the plugabble authentication module. Again specific use-case here. At work we want to allow people to ssh to some systems (to access serial consoles, etc), and we wish their connections to be tested against our internal single-sign-on mechanism. That could have meant a whole new PAM module, which would do XML-RPC-fu. Instead it meant packaging libpam-external - which is a neat PAM module allowing you to specify a shellscript to validate users & passwords. (libpam-external is very similar to mod_authnz_external which is a similar pluggable Apache2 module) So, this week "kernel hacking", & "pam hacking". Does that make me a real developer now? ObQuote: Time Bandits

I'm doing some contracting work at a local firm, and one of the little details that I have been pleased with is the fact that they seem to do introductions for people. On my first day, I was taken around and introduced to everyone, despite the fact that I probably won't be there long term (depending on where we go and when). Today, they were showing around a guy who will be doing a sort of student internship there, and once again, they stopped by my office. I appreciate that a lot, and think that it's a good thing for a group of people to at least have a bit of an idea who newcomers are. One of the things that I have always loathed, and vowed to do differently should DedaSys ever be more than myself, is feeling like an animal in a zoo when The Boss brought someone into the office to take them on a tour, pointing at us developers and talking about what we do, with no reciprocity. "This is Dave, one of our open source guys, who is really into Linux. He once roamed the temperate forests of Oregon and his mating season is from early January to late December." We get pointed at and talked about, and the other person remains a Mysterious Stranger. Granted, it's not always possible to disclose everything, but I think that you can still do a lot to make people feel respected without spilling the beans on a big potential customer or investment.

Just as a personal reminder for the next time I need that:

If there's a machine, for example a Xen host, with just one harddisk and you want to be somewhat safe in case of a disk failure, you can add a second disk and setup a RAID1 (mirroring). It's most simple to shutdown the machine and setup the RAID1 for the dom0. Afterwards you can start the domU VMs again when you're using LVM for their virtual disks. Following these steps will add RAID1 underneath your LVM setup:

0. /dev/sda5 is your current physical volume for your LVM, on the second (equally partitioned) disk /dev/sdb5 will be your starting point for your RAID1 (/dev/md3)
1. create a degraded RAID1 on /dev/sdb5:

# mdadm --create /dev/md3 --level=1 -f --raid-devices=1 /dev/sdb5
mdadm: array /dev/md3 started.
# cat /proc/mdstat
md3 : active raid1 sdb5[0]
135540288 blocks [1/1] [U]

2. prepare it for LVM and add it to your virtual group:

# pvcreate /dev/md3
# vgextend /dev/vg /dev/md3
Volume group "vg" successfully extended

3. move the extends from one disk to the other and be verbose to watch the progress:

# pvmove -v /dev/sda5
Finding volume group "vg"
Archiving volume group "vg" metadata (seqno 22).
Creating logical volume pvmove0
Moving 192 extents of logical volume vg/ts2-swap
Moving 1536 extents of logical volume vg/ts2-disk
[....]
Found volume group "vg"
Removing temporary pvmove LV
Writing out final volume group after pvmove
Creating volume group backup "/etc/lvm/backup/vg" (seqno 31)

4. remove the old partition from the virtual group:

# vgreduce /dev/vg /dev/sda5
Removed "/dev/sda5" from volume group "vg"

5. add the old partition to your raid and set it active:

# mdadm --add /dev/md3 /dev/sda5
mdadm: added /dev/sda5
# cat /proc/mdstat
md3 : active raid1 sda5[1](S) sdb5[0]
135540288 blocks [1/1] [U]
# mdadm --grow /dev/md3 --raid-devices=2
# cat /proc/mdstat
md3 : active raid1 sda5[2] sdb5[0]
135540288 blocks [2/1] [U_]
[>....................] recovery = 0.2% (284480/135540288) finish=39.6min speed=56896K/sec

6. let the RAID1 doing its sync and you're done.

Just as a small side note:
I don't know why the kernel don't want to boot when it get passed root=/dev/md2 as a kernel parameter. It works with root=/dev/sda3, though...

According to a recent article, 6 Common Website Mistakes That Cost Money are:

1. JavaScript or other crawler-unfriendly navigation that may impede indexing

This one is best avoided at design-time, by including Web Content Accessibility Guidelines 1.0 Level A in the design brief, but if you’ve ended up with JavaScript-based navigation on your site (check by doing “View Source” and searching for the code for your home page link and so on - if you can find it, then it’s probably not javascript) and it’s based on some template system, a webmaster can probably do a whole-site edit to put the navigation links in the page properly - or at least add a useful <noscript> tag.

2. Navigation that buries important pages within the site architecture.

The structure of the website’s files and the structure of the link menus do not need to match, so if there’s a page that you feel is important, get your webmaster to add it to the navigation links across the whole site.

3. Duplicate “pages” getting indexed under multiple URLs.

This usually happens for one of two reasons: one is inappropriately-parked domains, which is mistake 6 below and often fairly easy to fix; the other is a misbehaving web application, which you’ll need to get a programmer to fix. You can do a simple test of your web application by starting at your homepage and following links to a particular page; then open a new browser window and try to reach the same page by different links (or a site search) and compare the address bars (the bit of your browser showing http://) - do they match? If not, you’ve got this problem.

4. No keyword phrase focus in the content or conversely, keyword phrase stuffing

You can use a good word-counter on the text to see how common different keywords and keyphrases, or use the “webmaster tools” section of some search engines to see what they’re focusing on. Keyword-stuffing can be fairly easy to see. If you “View Source” on a page and there’s a large block of keyword-intensive text somewhere in it that doesn’t appear it when viewed in a browser, then it’s probably stuffing. Many sites regard stuffing as a sort of spam, so you don’t want to be found doing this. To fix these problems, rewrite the page text appropriately.

5. An optimized home page, but that’s it

Repeat your checks from problem 4 on a few pages other than the home page to discover whether you suffer from this. Also, see whether your website statistics show search engine visitors arriving at a variety of different pages (these are sometimes called “Entry Page” statistics).

6. Additional domains owned by the company are not properly redirected

If you usually use .co.uk, but you also have a .com domain, try visiting a random page on your website, then click in the address bar and replace the .co.uk with .com - what happens? If the page is Not Found, then your domains aren’t properly redirected and you need a Redirect adding to the second one. If the page displays but the address doesn’t change itself back, then your domains are probably pointing at the same webspace but aren’t properly redirected, which will mean you’re probably making mistake 3 above. Usually, the simplest way to fix this is with a conditional redirect. On Apache webservers, you can add a .htaccess file containing something like:-

RewriteEngine On
RewriteCond % HTTP_HOST  !^www\.yourdomain\.co\.uk$ [NC]
RewriteRule (.*) http://www.yourdomain.co.uk/$1 [R=permanent,L]

That even works on BT Business web hosting, by the way. If it doesn’t work, try asking your web hosting provider to enable mod_rewrite for you or ask them to suggest how to achieve the same result.

The above list of mistakes was published on Search Engine Land last week. The correction methods are all things used by my webmaster cooperative.

Computer security is generally defined as the following:

1. The data should remain available to those who need it.
2. The data should not be available to those who don t have the right to.

The critical software component to the first item is your well-known nightmare: the backup software. Backups are easy! In many corporate environments, here is how you ensure you have backups:

• you install the backup agent,
• you call/mail the backup guy, telling him the IP of the machine and what to backup,
• you wait for his call/mail telling you it s ok.

Isn t that cool? So little work to have all your data completely safe! Wait if you look more closely, there is something wrong here. Nowhere in this process did you specify credentials to the backup guy, nor did you add anything to identify the backup server. Or to say it otherwise, once you have installed the backup agent, the backup server has full access to your data. But you didn t even specify anywhere the IP of the backup server. So this means that anyone on the network has full access to your data. Which, while trying to make your data secure, actually brings a gaping security issue on your system. Security by nullity When you install a well-designed backup agent, like Bacula, you have to specify a password for each client and make this password known to the backup server. A simple authentication protocol ensures that only the backup server is able to backup your data. However, when you install, for example, the HP Data protector agent, it starts listening on a TCP socket and (no kidding!) binds it to a restricted shell which has access to a small list of commands. The backup server only needs to connect to this TCP socket and issue commands. While this has the great advantage of simplifying the development process of the backup server, such a software has a name: a rootkit. Several other proprietary backup software have different implementations, like RPC-based or proprietary protocols, but the basis remains the same: you connect to the TCP port, and you have a way to read absolutely any file on the system. Of course, there are so-called security options, that you can buy besides the disk agent or the nifty web interface. Yes, when you buy software that is critical for your security, the very lowest level of security that you d expect from any software not turning your box into a self-service is a paying option. In the end, what prevents your data from being available to anyone on the intarweb is the ultimate solution to everything(tm): the firewall. As people are not stupid enough to use the same backup system in the DMZ, you can t simply bounce from it after having used a hole in the lousy PHP code that is never updated. (Well, that will still work in many cases since people actually are stupid enough.) No, what makes it very fun is the backup network. The hackup network A tape library is expensive hardware, therefore you only want to buy one. However, when you have several departments or, in outsourced environments, several clients, you can t simply access to the backup agents on all these servers, because of all these evil routers and firewalls that are blocking you. The solution is trivial: use the second network card on all servers to connect to a backup network. The backup network is entirely managed by backup people who have no idea of network security, and is routed all the way down to the backup server. If you are lucky, some ACLs set up by the network guy who plugged the switch will prevent some parts of the network to access some others. In all cases, it s very likely that many people in the company (or from other companies!) have full IP access to all your private servers where sensitive data is stored. That includes access to your databases setup without a password, and of course to your highly secure backup agent. That generally also includes full IP access to the lousy maintained backup server, on which security updates are never installed. But don t worry. Your data is safe. Note: no, this is not a worst-case scenario. Such badly-designed software is widespread. Such practice is widespread in several companies I know.

I had a problem where the email address circsales@washpost.com spammed a Request Tracker (RT) [1] installation (one of the rules for running a vaction program is that you never respond twice to the same address, another rule is that you never respond to automatically generated messages). Deleting these tickets was not easy, the RT web interface only supports deleting 50 tickets at a time. To delete them I first had to find the account ID in RT, the following query does that:
select id from Users where EmailAddress='circsales@washpost.com'; Then to mark the tickets as deleted I ran the following SQL command (where X was the ID):
update Tickets set Status='deleted' where Creator=X; Finally to purge the deleted entries from the database (which was growing overly large) I used the RTx-Shredder [2] tool. RTx-Shredder doesn’t seem to support deleting tickets based on submitter, which is why I had to delete them first. I am currently using the following command to purge the tickets. The “limit,500” directive tells rtx-shredder to remove 500 tickets at one time (the default is to only remove 10 tickets).
./sbin/rtx-shredder --force --plugin 'Tickets=status,deleted;limit,500' There are currently over 34,000 deleted tickets to remove, and rtx-shredder is currently proceeding at a rate of 9 tickets per minute, so it seems that it will take almost three days of database activity to clear the tickets out. I also need to purge some tickets that have been resolved for a long time, I’m running the following command to remove them:
./sbin/rtx-shredder --force --plugin 'Tickets=status,resolved;updated_before,2008-03-01 01:01:34;limit,500' With both the rtx-shredder commands running at once I’m getting a rate of 15 tickets per minute, so it seems that the bottleneck is more related to rtx-shredder than MySQL (which is what I expected). Although with two copies running at once I have mysqld listed as taking about 190% of CPU (two CPUs running two capacity). The machine in question has two P4 CPUs with hyper-threading enabled, so maybe running two copies of rtx-shredder causes mysqld to become CPU bottlenecked. I’m not sure how to match up CPU use as reported via top to actual CPU power in a system with hyper-threading (the hyper-threaded virtual CPUs do not double the CPU power). I wonder if this means that the indexes on the RT tables are inadequate to the task. I tried adding the following indexes (as suggested in the rtx-shredder documentation), but it didn’t seem to do any good - it might have improved performance by 10% but that could be due to sampling error. CREATE INDEX SHREDDER_CGM1 ON CachedGroupMembers(MemberId, GroupId, Disabled);
CREATE INDEX SHREDDER_CGM2 ON CachedGroupMembers(ImmediateParentId, MemberId);
CREATE UNIQUE INDEX SHREDDER_GM1 ON GroupMembers(MemberId, GroupId);
CREATE INDEX SHREDDER_TXN1 ON Transactions(ReferenceType, OldReference);
CREATE INDEX SHREDDER_TXN2 ON Transactions(ReferenceType, NewReference);
CREATE INDEX SHREDDER_TXN3 ON Transactions(Type, OldValue);
CREATE INDEX SHREDDER_TXN4 ON Transactions(Type, NewValue);

• [1] http://bestpractical.com/rt


• [2] http://search.cpan.org/~ruz/RTx-Shredder-0.07/

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I’ve had little time in the four years I’ve lived in Roslindale to get involved in community volunteer efforts. My wife Rachele, however, has devoted several years to efforts such as the Roslindale Community Center, Roslindale Village Main Streets, and Roslindale Clean and Green. She has served as chair of both RCC and one of the RVMS committees. Over the past few months, I’ve been disappointed to see the RCC board endure repeated senseless attacks by a perhaps overzealous community member, Walter Michalik, who has effectively paralyzed the organization. I have nothing personal against this guy, but I thought I could do my part here by publishing an example of an email he broadcast to the committee, which I think is embarrassing enough on its own merits to need no editorializing from me, except to say any email that starts with “just so you won’t be surprised when the IRS launches its investigation” can be neither productive nor taken seriously. The context is a response to an announcement sent out pursuant to the Community Centers By-Laws scheduling a special meeting to discuss the recent upheaval on the Council. There’s no reason this should not be in the public record:

Rachele Just so you won’t be surprised when the IRS launches its investigation, be advised that YOU DO NOT HAVE THE AUTHORITY TO CALL FOR A SPECIAL MEETING. The By Laws do not allow the President/Chair to call for a Special meeting - that right is reserved for the MEMBERS to have a power over a hostile or non-performing President/Chair. It was created by a Membership wary of annimosity within its ranks in order to protect itself from falling into a useless dysfunctional body. That’s why our By Laws require the majority of the membership request it through the Chair and not the other way around. So you screwed that up too. Your continuous violation of rules and laws have proven beyond a doubt that this current Roslindale Community Center Council has violated the trust behind its IRS-designated not-for-profit status. The failures are on so many significant levels over 6 months it is readily apparent that the Roslindale Community is better served without a Community Center Council. There is no longer any excuse to allow the residents of Roslindale to be denied the services they deserve that you and the officers have no idea how to deliver. Because that’s what you are supposed to do - serve the residents of Roslindale and not preseide over a self-serving board. You’ve taken us from dysfunctional to non-functional over the past 60 days. You and your officers have already driven away our Archdale partners and now the merger is off. Congratulations. You got what you wanted. You and the officers have withheld information from the Members of the Council imposing gag orders along the way and in more than one instance spreading lies within this community. There are so very many lapses on your part and the rest of the officers that it is very apparent that the Roslindale Community Center exists IN SPITE OF the Roslindale Community Center Council - not because of it. It would be far better indeed, if the Center were run without the Council. What have you done in 6 months? All you do is avoid the work of leadership. Please, just gracefully step aside and let a real leader emerge - or dissolve the Council and let the Center run itself under BCYF before the IRS makes that happen. Of course this is my stated opinion. You can choose not to belive it. You can huddle with a group of self-serving officers and invent excuses or change the agenda away from the message and continue with your ad hominem attacks against the messenger. I’m thick-skinned. Feelings aren’t important to me - services to residents are important to me. While I have, in fact, enjoyed the confidences of others within this community and their true displesure with this Council, I will produce that to the appropriate authorities as I see fit along with the Bill of Particulars I have produced with documentation for all charges. As a founder of the Roslindale Community Center Council I can no longer support you or the officers as any legitimate authority in this community.

Technorati Tags: Boston, Roslindale, Walter Michalik

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Ah, Dell. Seeming inventors of the tech support pit of bureaucratic indifferences, inventors of the flamingo pink Inspiron, perpetrators of fraud in New York...

I have, for over a year now, been on a crusade trying to get them to stop sending me their Dell Home and Home Office catalog to my mailbox. It has been a bundle of fun, let me tell you.

They have a nice-sounding privacy policy. It says you can opt out of all their mailings by filling out a form online. Yeah, good luck with that. First of all, there are different forms for different departments at Dell. I've filled out them all, multiple times. They do nothing whatsoever. Perhaps they use them as lists of known-good addresses to send new advertisements to, rather than lists of people to remove. Oh well.

Now, unfortunately I feel compelled to bore you with the saga so far, involving telephone hang-ups, broken privacy policies, and the like. But there is a silver lining at the end, in which I submitted a request to the postal service asking them to block Dell from sending me any more mail, and it appears that they are very likely to violate Federal Law any day now.

I have called them about it. Dealt with the old "let me transfer you to the correct department" then hang up on me ploy. Spoken to people that have promised up and down that I'll be off their list in 30-60 days. It's always 30-60 days, isn't it? Very convenient that I can't tell for 2 months whether or not they've processed my request.

I've tried their online chat. One of my attempts went like this:

Session Started with Agent (Sneha Ranga)

Agent (Sneha Ranga): "Due to circumstances that have affected Dell Communications I am temporarily unable to pull up any information. The down time is temporary. We apologize for the inconvenience, as we value your time as a customer. Please contact us back after an hour."

Session Ended

Ah Dell, only you could reach such a pinnacle of customer service. /kicking someone out of a chat room before they have a chance to say a word.

Finally, last fall, I blogged about the situation (that's the link above). Debbie from Dell red the post and emailed me. Great, I thought. She asked for my address information and catalog information and sent me a removal confirmation:

From: Debbie@Dell.com
Date: Thu, 18 Oct 2007 13:08:18 -0500
To: jgoerzen@complete.org
Subject: RE: Dell mailing list

Thank you, Mr. Goerzen, your request to have the below address
information removed from our marketing lists has been received:

[ my address here ]

We will process your request promptly. However, it may take several
weeks for some changes to take effect. If you are still receiving
catalogs after thirty (30) days feel free to email me. Sorry for any
inconvenience you may have experienced.

Thank you,
Debbie

So that was October. In December, I replied to that message, saying: "I received another mailing today, and it's been nearly 2 months since your initial message. If there's anything further you can do, I'd appreciate it." Debbie said, "I am very sorry Mr. Goerzen, I will resubmit your request." Guess how successful that was.

So in February, I manage to figure out a way to send in a support ticket without having a Dell system serial number. I wrote:

I keep getting your Dell Home and Home Office catalog. I have tried for months to get off your mailing list. I have called in, talked to people in multiple departments, who have promised to remove me from the list. I have contacted you online. NOTHING IS HELPING. This has gone on for MONTHS.

PLEASE NEVER SEND ME MAIL AGAIN, EVER, AND DO NOT RENT OR SHARE MY NAME.

My address is above.

The code on the mailing I received is: [ snipped ]

The form letter I got back said:

If you are currently receiving our catalog or mailings and would like to be removed, please visit the following web page and select the appropriate link under the "Opt-out of direct mail, phone or fax communications" heading: http://www.dell.com/OptOut

I replied, saying that form didn't work. Guess what I got back?

Thank you for signing up for Dell Email Subscriptions. Please save this email for your records.

Yes, that's right. Asking them to take me off their postal mailing lists got them to PUT ME ON their email lists. ARGH.

So they eventually manage to correctly take me off the email list, and of course promise to do the same with the postal list. This back in February.

I contacted them again in March and July, only to have a similar stupidity-laced run-in with clueless form-answer-laden Dell support reps. Each one claimed to have now, finally, and permanently removed me from the list. It never happened, and none of them lifted a finger to find out way, and no amount of begging could make them.

So, here's the good part.

Junkbusters has spent years educating people on how to get rid of unwanted mail, and documents getting a prohibitory order against the sender. It was originally designed for people that didn't want to receive obscene advertising mailings, but thanks to the happy fact that one non-adult-mailer challenged a prohibitory order all the way to the Supreme Court, you can now get prohibitory order against anyone. Yes, even Dell. (The supreme court's ruling even gave an example: you can prohibit a clothing catalog if you want.)

And last month, that's exactly what I did. The USPS sent me back a copy of the letter they sent to Dell, as well as a second page with instructions on reporting violations. Here's the letter they sent to Dell:



Somehow I get a chuckle over some Dell mail clerk trying to figure out how an 11-pound laptop is sexually provocative.

From August 25 on, it is a federal offense for Dell to send me another Home and Home Office catalog. This is a branch of criminal law, not civil law. That is, it's the maybe-go-to-jail branch of law.

How disappointed I was to receive yet another catalog from them today. If only they had waited 5 more days, I could have turned them in now.

Oh well. There's always next month's catalog. Let's just hope the clerk that received the USPS letter removed my name with a better system than everyone else at Dell uses, eh?

Recently I fixed my OpenVPN tunnel and figured out what was wrong with my bridge setup. Here is the complete setup that I have. Server I wanted to have as much of the configuration on the server as possible so that I could easily add more clients and wouldn't have a need to update client configuration when ever the server preferences change. Here is my OpenVPN server configuration:

mode server
tls-server
dev tap0
server-bridge 10.5.6.1 255.255.255.0 10.5.6.200 10.5.6.209
ifconfig-pool-persist /var/run/openvpn-ip.txt
keepalive 10 60
ping-timer-rem
persist-tun
push "route 10.5.6.0 255.255.255.0"
push "dhcp-option DNS 10.5.6.1"
ca /root/easy-rsa-2.0/keys/ca.crt
key /root/easy-rsa-2.0/keys/ressukka.net.key
cert /root/easy-rsa-2.0/keys/ressukka.net.crt
dh /root/easy-rsa-2.0/keys/dh1024.pem
client-to-client
up /etc/openvpn/ovpn-ressukka.sh

and the up script:

#!/bin/sh
# Bind the tunnel interface to the bridge
BRIDGE=br0
ifup $1
brctl addif $BRIDGE $1

There is nothing really special about that configuration. The server is in TLS mode configures a bridge. The keys are generated with easy-rsa by following a openvpn howto entry. The up script just binds the tap0 device to the network bridge after bringing up the device. Next I created the interface configuration by adding the following to /etc/network/interfaces:

iface br0 inet static  
 address 10.5.6.17  
 gateway 10.5.6.1  
 netmask 255.255.255.0  
 bridge-ports eth0

The trick here is to create a single bridge with just the eth0 device. We use the up script for openvpn to add the tunnel device to the bridge. Otherwise the bridge would never contain the proper devices. Client As for the client, you simply set the client to use the CA-certificate and Host key created with easy-rsa, set the hostname and tunnel type. Tunnel type is assumed to be a tun-device instead of tap, so in my case I needed to change it too. There is no need to tell the client anything else. Everything else will be negotiated through the tunnel. And since I use NetworkManager to set up my tunnels I didn't have a need to drop in to a shell even once at the client.

I've been meaning to write up on this for quite some time now, but always have something seemingly more important things to do. Most modern Linux distributions offer ways to manage network interfaces via some kind of abstraction. Usually this abstraction allows one to dynamically rename and add network interfaces. For Debian family management is done with ifupdown, while with RedHat family it's sysconfig. In addition there is NetworkManager which is a cross platform solution for dynamic network configuration (which eliminates the need to rename interfaces). Case Xenserver Usually this comes in rather handy, but on other occasions it can be a pain. A while I was helping out with an installation of a XenServer instance. This server had, for some reason, ethernet interfaces reversed in comparison to the other XenServers on the site. Luckily the service console has the network configuration in ifcfg scripts. We were easily able to reverse the interfaces by binding the interfaces to certain hardware addresses. The only problem is that the interface is renamed only when the interface is brought up. What's worse the interfaces were enumerated before the server would bring up all of the interfaces. Only eth0 was brought up for management purposes before enumerating. This means that the original eth0 was renamed to _tmp_xxxxxx. The (oh so elegant) solution was to create a script that does ifup eth1; ifdown eth1. Problem solved. Case tap0 I also experienced similar problems when I was setting up my OpenVPN tunnel. I wanted to use a bridged connection to my network, but for that I needed to create a br0 interface with tap0 as a member. It's easy enough to create ifupdown configuration to set up tap0. Hook that up to br0 and you are all set. The same problem will bite you here. The interface tap0 is actually created only when the tap0 is brought up and br0 members are added only if they are present. The solution? In my case, create a custom script that adds the device manually after it's been created properly. I was unable to find anything that works without using a custom script =( In retrospect Looking back at these cases, I should have known better. The problem was obvious and it took me way too long to figure out the cause for my problems. Then again, the utilities should be able to create a reasonable abstraction for themselves that they use to determine the actual status of the whole system. This way the trickery needed for setting up simple interface would be obsolete. You can't have it all, but you can always hope.