More connections will use more RAM, but how much?  We don’t want to overcommit, as the connection tracker uses unswappable memory and things will blow up. If we set aside 512MB for connection tracking, how many concurrent connections can we track?

There is some Netfilter documentation on wallfire.org, but it’s quite old. How can we be sure it’s still correct without completely understanding the Netfilter code? Does it account for real life constraints such as page size, or is it just derived from looking at the code? A running Linux kernel gives us all the info we need through it’s slabinfo proc file.

We can peek at how the kernel is using RAM using the proc file /proc/slabinfo and clear this up.  The nf_conntrack entry from here tells us, on one particular firewall, that there are 26,702 active entries (or objects), that each object is 304 bytes in size and 13 of them fit in each slab (and that each slab is 1 kernel page).  So we know that conntrack entries take up 304 bytes each.  But if we’re going to be accurate, then we have to account for the overhead of the kernel page size.

The Linux kernel uses a slab memory allocator, so rather than allocating 304 bytes every time a conntrack entry is needed, they are allocated in “slabs” of one or more kernel pages which reduces memory fragmentation and improve performance.  When they’re done with, they’re not immediately freed - instead the memory is reused the next time another object of the same type is needed.

In the kernel we’re using, the page size is 4096 bytes. As slabinfo told us, 13 nf_conntrack objects fit in each slab and each slab takes up 1 page. 13 objects of 304 bytes is 3952 bytes in total, which leaves 144 bytes of waste per slab.  So every 13 objects we waste 144 bytes. So a nf_conntrack object consumes about 316 bytes on this box, giving us almost 1.7 million entries for our 512MB.

You can get your kernel’s page size with the command: getconf PAGESIZE. The slabtop program, installed on most modern GNU/Linuxes, shows the info from /proc/slabinfo it in a pretty table and lets you sort the values.

For those of your with short attention spans, I finally get started with the talk at about 2mins 30, and start singing the first article, Otitis Media, at about 7mins.

Hugh’s answer genuinely made me think this was an early April Fool’s joke. In fact I’m still not sure Medialens aren’t making me look like an idiot:

No proof, but circumstantial evidence and reasonable presumption of AQI [al-Qaeda in Iraq] involvement - very much their modus operandum. Suicide attacks are their signature method, and this was a dramatic detonation suggesting a lot of explosive - again, very AQI.

And…who else would do this?

So, process of elimination, history of AQI attacks in Diyala etc.

And the logic of it Sunni Arab vs Iraqi Kurds. As a man in Jalawla told Reuters:

“Al-Qaida is targeting the Kurds because it believes that
we are involved in the political process and collaborating
with the Americans.”

This blows my mind. “very AQI” and “a man in Jalawla told Reuters”. “Who else would do this?”

As Medialens point out, the BBC claim they are “committed to evidence-based journalism”. Except they pick and choose when their committment applies, such as when they refused to report the use of banned weapons by US forces in their November 2004 assault on Falljuah.

I got to have a bit of a nosey around the Manchester BBC building too - though I was worried I’d open the wrong door and end up on TV. Didn’t fancy having to apologise to Jeremy Paxman.

Brightbox also sponsored some pizza, and gave away t-shirts and stickers like candy (there was no candy though).

My slides are available here, and contain a little example file system indexer. I made my slides with webby and S6 if you’re interested.

The main gripe appears to be with “women only” conferences, such as the Women on the Web conference, organised by a group called Forward Ladies, or the Geek Girl dinners.

I think a fair summary of his, and some other commenters, opinion is that these “women-only” events don’t help the effort to get more women involved in technology. Comparing it to positive discrimination in many ways.

Women Friendly

The way I see these events is more “women-friendly”, rather than “women-only”.  With Geek Girl dinners, this is explicit, as men can attend at the invite of a women. A simple, but generally effective heuristic to select for friendliness to women.

With Women on the Web, it’s less clear, but nowhere does it state men are not welcome.  The same goes for the Forward Ladies membership terms and conditions. I’m not sure how Dom knows this event is women only (I’ve emailed Forward Ladies for more info).

Until I’m shown otherwise, I’m assuming the Women on the Web conference is women-friendly, not women-only.  Of course, if you browse the site you see photos of women, and all the past speakers appear to be women, and this might not be that inviting to men - but how inviting do you think Infosec is to women, with photos of rooms full of men, and women in skimpy clothes giving out leaflets? Perhaps all the speakers are women because they just don’t get many men interested - maybe men just  need to be thicker skinned and ask to be involved.

As an amusing side note, after checking the Infosec url was correct I caught sight of this year’s branding - hundreds of what I assume are just people, but they happen to be using the pretty well established symbol for “men” (let’s not get into that though).

Demand

You only have to see the turnout of women at Leeds Geek Girl dinners compared to the turnout of women at Leeds Geekup to know there is a demand for these women-friendly events. For whatever reasons, some women are more likely to go an explicitly women-friendly geek event than another random geek event. Of course women should be encouraged to come to all events, but not all events are equally friendly to women, and it’s often difficult to assess how friendly they are from outside.

Social Groups

Women are a social group  - they’ll often share some common experiences and outlooks due to their sex - due to society’s treatment of them as a group of people. This goes for men too. And gay people. And geeks. Etc.  When you see women in this way, you’d expect some of them to organise and attend these types of events. Most social groups do.

Geek Girl Dinners just have a convenient way of selecting women-friendly people: women, or men invited by women. Of course, not all women are women friendly  - that is just a stereotype, but it seems to work for them.

Largely though, I think if you name things and brand things right, you get the people you’re hoping for. Maybe that’s why Infosec is a sausage-fest.

Update

Forward Ladies has confirmed that men are welcome to Women on the Web, and are welcome as members of Forward Ladies too. They also run 50/50 events “to which men are specifically invited”.

More Leeds Market photos here on my Flickr profile.

From the site:

“Techietubbies is a weekly podcast covering a multitude of subjects, from a round up of the week’s tech news, live callers, competitions, questions and answers… and beer :)”

Though I’m driving, so no tech news for me. I think it’s recorded if you can’t see the live thing.  It’ll be broadcast live here via ustream.tv

I realised that having tinkered with computers heavily almost my entire life, a lot of my “computer skills” have shifted into the intuitive, automatic systems.  I obviously (hopefully) use the rational systems a great deal, but underlying it is definitly intuition - the gut feeling of where to go next to solve the problem.  I regularly come up seemingly random avenues of investigation that lead to gold and I couldn’t say with any certainty why I thought of it.  I’m assuming this is the same for most computer geeks (and chess geeks, cooking geeks, music geeks etc. :).  It’s become a native language for us.

I don’t think the average rational system can easily deal with very complex problems.  It’s great for some more-linear concentrated work or planning, but for big stuff with lots of parts - hard work.  I think I usually research and “pre-process” a bunch of material around a problem using my rational system, then my automatic system gets to work mulling over the bigger picture.  Then when I’m making rational decisions about it, I’m heavily informed by the intuition. Or sometimes just when I’m showering.

Anyway, not sure where I was going with this other than a “aren’t I great” blog post. The summary would be, don’t rely on your rational systems so much. Give the intuitive some good mulling time. And shower regularly.

Louisa and I put this together in just a few days, me coding and Louisa designing. Was a fun little project to do.

“We have customers who build engines for aircraft. I am happy they are not using freeware when I get on a jet.”

That’s pretty funny. She’s basically saying

“It’s better to build important things with tools you can’t examine for yourself.”

SAS claim to have over 40,000 customer sites worldwide.  The news article claim 250,000 people use R regularly.  The difference here isn’t in the numbers of users, it’s that, with R, every user is a potential developer.  SAS can’t possibly compete with that.

My mate Paul Brook is talking about RAID on Linux too.

Come along for the talk, or the beer, or the socialising - or all three.

Small pumpkin I carved today, with a carrot for a nose. It seems that I missed all the trick or treaters though. More chocolate for me and Louisa then.

Louisa is cooking a lovely smelling soup with the innards from him. A couple more photos here.

The git user manual describes submodules but it took me a while to figure it out, so I’m hoping these examples will help others (and me again when I forget and find my own page when googling about it :)

These examples deal with your_project and the project you’ll be adding as a submodule, other_project

Adding a submodule to your_project

$ git submodule add git@git.example.com:other_project.git other_project
Initialized empty Git repository in /home/john/dev/your_project/other_project/.git/
remote: Counting objects: 59, done.
remote: Compressing objects: 100% (59/59), done.
remote: Total 59 (delta 22), reused 0 (delta 0)
Receiving objects: 100% (59/59), 8.33 KiB, done.
Resolving deltas: 100% (22/22), done.

This clones other_project and sets up the .gitmodules config to your_project and adds them both ready to be committed. You’ll notice that the other_project directory is added, not all the files within. Git just records the commit id from the other_project repository and uses that when cloning - a bit like a tag.

$ git status
#	new file: .gitmodules
#	new file: other_project

So now commit those changes:

$ git commit .gitmodules other_project -m "Added other_project submodule"
$ git push

Cloning a tree with submodules

Git doesn’t automatically fetch all your submodules, so you need to do the following after cloning your tree:

$ git submodule init
Submodule 'other_project' (git@git.example.com:other_project.git) registered for path 'other_project'

$ git submodule update
Initialized empty Git repository in /home/john/dev/your_project/other_project/.git/
remote: Counting objects: 59, done.
Receiving objects: 100% (59/59), 8.33 KiB, done.bjects:  91% (54/59)
Resolving deltas: 100% (22/22), done.
remote: Compressing objects: 100% (59/59), done.
remote: Total 59 (delta 22), reused 0 (delta 0)
Submodule path 'other_project': checked out '6d5ca374208715501832eb33ed6a70022a3bb60c'

Updating a submodule

So somebody pushed some updates to other_project and you want them in your_project:

$ cd other_project
$ git pull origin master
Updating 6d5ca37..235996d
Fast forward
 5 files changed, 100 insertions(+), 10 deletions(-)
$ cd ..
$ git add other_project
$ git commit otherproject -m " Updated other_project submodule to latest HEAD"

If you want a particular commit rather than the head of master, then just specify that commit id on pull (instead of master). If you want the head of a particular branch then specify that branch name instead of master.

It is important not to have a trailing slash when you add other_project as this will treat it as a normal directory, adding all the files within it to your_project and forgetting about it’s submodule status

Making changes to a submodule within your_project

To make changes to other_project within your_project tree, you need to explicitly checkout a branch first:

$ cd other_project
$ git checkout master
...make your changes...
$ git commit -a -m "Fixed a bug"
$ git push
$ cd ..
$ git add other_project
$ git commit -m "Updated other_project"

You need to remember to push changes to other_project before you push your_project else others won’t be able to clone your_project properly as it will reference commits to other_project that haven’t been published yet!

Louisa and I randomly came across this demolition in Armley back in July, 2007. I happened to have my big camera with me.

Under the new law, spammers can be fined £5,000 in a magistrates court or an unlimited penalty from a jury.

Yet it appears it is really up to me to pursue charges through the courts. The Information Commissioners Office, who enforce the new regulations, appear largely neutered (as predicted):

If my complaint is upheld, will the organisation be punished?

If we think the organisation has breached the regulations, we can ask them to put things right, but we cannot punish them for breaking the law.

If my complaint is upheld, will I be entitled to compensation?

We have no powers to award compensation . If you have suffered a loss because an organisation or individual has broken the law, you may be entitled to compensation, but you must claim this through the courts.

The right to compensation applies even if you don’t report the problem to us. You can make a claim to the court whether or not we have agreed that the law has been broken.

No doubt this will cost a lot of my time and money. We should build a simple kit, with some form letters and instructions on pursuing compensation.

Or just take enforcement into our own hands and report them to something like Spamhaus.

Here is a video of me performing the Wikipedia article “Otitis Media” (which I also performed live at The Chemic Tavern on Thursday and at Bar Camp Leeds just today).

Record your own, upload them to You Tube and submit them to us!

The Open Rights Group are a UK based organisation fighting for our civil liberties in the digital age. DRM, e-voting, copyright term extensions, FOI, net neutrality, privacy, RIPA, creative commons etc.etc.etc.etc.etc. They’re like an English EFF.

They have a tiny staff and many other volunteers who are extremely dedicated to the cause and are working very hard for our freedoms.  They are funded entirely by donations which pays for the staff, an office and expenses of running campaigns and pestering politicians.  They’re currently hoping to push their income up so things are more sustainable.

So, please sign up and give them some money every month. Anything from £5 upwards would be super. If you use computers for pretty much anything, it will make your life better - or at least prevent it getting any worse.