The flights are booked for the summer

U2 Vertigo Tour 2005 I’ve finally booked flights for me and Stéphanie for the summer! We’re going to the U2 Vertigo concert in Copenhagen on the 31th of July, and after that I’ll be going to Århus and Aalborg to visit friends and family while Stéphanie goes back.

SWISS logo We’ll arrive in Copenhagen on July the 31th with a flight from SWISS and Stéphanie will go back already on August the 2nd. I’ll then take a bus to Århus and Aalborg and first go back two weeks later on the 16th of July.

In those two weeks I hope to visit lots of people in both Århus and Aalborg!

That was the dates — now let me tell you about the booking experience… First of all: it’s a jungle trying to find the cheapest flight from A to B. There’s the cheap airlines like EasyJet and Ryanair, and I’ve flown with them before without any problems. But neither of them fly directly from Switzerland to Copenhagen which means that you’ll have to go by either London Stansted or Berlin and this complicates the whole thing, and is also likely to make the total cost higher than a direct flight.

About the total cost, then that’s a bit silly too: half of what you pay is called fuel, fees and taxes. And you’ll only see those at the end of your booking. I understand that the airline companies have to pay something to the airports to be allowed to land there, but could they not just include that in the price? That would make things more transparent when you’re comparing prices — ups, perhaps that’s why they haven’t done it! :-)

Finally a technical thing: the SWISS online booking system cannot handle two concurrent bookings made in the same browser. When trying to do so, you get this nice little warning:

Sorry: our system is unable to continue this transaction. Entering multiple inquiries or using the “Back” function of your browser can cause the system to freeze. Please close your internet window completely and start again.

I would suspect that they store the session data in a cookie, and thus the two tabs or browser windows will use the same cookie. That’s a shame, for making two concurrent bookings is exactly what I had to do in my case where Stéphanie and I will be flying back on different dates. And it’s not that it’s technically impossible to support multiple concurrent sessions in the same browser: it just requires that the session ID is embedded in the page and not in a cookie — EasyJet does it like this. A small detail in the implementation with a big impact on the functionality of the system as a whole.

Using Linux it was easy to overcome this limitation anyway: I simply logged in as another user, exported $DISPLAY to :0.0 and started another Firefox. Before doing this you’ll have to give the other user access to your X server, do this by copying your ~/.Xauthority file to the home directory of the other user. An alternative is to make a symbolic link to it and then ensure that the other user is able to read it (with root this works very nicely).

Another, more heavy-weight, solution would be to spawn a new display using something like GDM Flexiserver, but just copying or linking the ~/.Xauthority file is much easier, IMHO.


  1. Mikkel:

    Hey maybe I’ll see you around by then. I will be working in Århus as usual. If I survive the exam tomorrow that is…

  2. Martin Geisler:

    I hope so! Good luck with your exam — and don’t worry, I’m sure it wont be a problem!

  3. Thomas Mølhave:

    Maybe we could gather the crowd for some beers and a movie?

  4. Mikkel:

    Not dead yet. And yeah, we should gather the crowd - it’s been a while.

  5. Martin Geisler:

    Yes, that would be cool! Are you in Århus the whole time or how does your vacation look?

    Oh and let me just say that your and Lars’ paper look super, like, eh, a real paper! :-) And I like the fancy title: Assignment Featherweight java: Bringing Mutable State to Featherweight Java, even though you have two typos in it on your website…

  6. Thomas Mølhave:

    I’m going to Paris with Mikoline and my sister and her boyfriend from the 3th to the 10th of July, I have no significant plans for the rest of July and the start of August, so we will definitely be able to find a date.
    Oh, and I am glad you liked our TOOL project, the “paper” look&feel was mostly a joke, but we did spend quite a lot of time perfecting the layout and the LaTeX (and you would find quite a number of the LaTeX techniques has been inspired by our dOvs project with all your fancy LaTeX code in it).

  7. Martin Geisler:

    Cool! Have a nice trip to France — and then we’ll figure something out when we’re all back in Denmark.

  8. Thomas Mølhave:

    Oh, and about the X stuff, couldn’t you just use “xhost +”, or “xhost +hostname” in a local xterm? (or something slightly more sophisticated if you are really paranoid)?

  9. Martin Geisler:

    Sure, but that would allow any host to connect to my X server — providing the root user (or whoever needs access) read access to ~/.Xauthority is more fine grained. So I think what I did what that “something slightly more sophisticated” thing you were talking about :-)

    And by the way: Giving just a single user read/write access to ~/.Xauthority is easy to do if you have a kernel with support for ACLs — Access Control Lists. I had to do an exercise in my System Security course about ACLs, and after that I figured that they were so cool that I wanted to have them in my kernel too!

    With ACLs you just do setfacl -m u:foo:rw file to give user foo read/write access. Much easier than creating a new group with just you and foo, but it also enables stuff that you cannot do with the normal Unix permission system. (Not that I’ve needed something like that yet… :-)

    Hmm… that was the theory, which I thought was working as I’ve just explained it — but now I notice that after I fiddled with my ~/.Xauthority file, then it is no longer updated on login! This means that I’m again the only user who can access my display — argh! I’ll have to play some more with it when I get some more time, right now I should finish the documentation for the Eiffel project I’ve been working on…

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