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Repair a Cassandra Cluster

I use the Cassandra database cluster system to manage a new set of websites and once in a while I start getting many errors and the website stops working altogether.

When that happens, it is likely that Cassandra broke something in the temporary tables that it holds. The only way to go past that problem is to clear those tables. Until then, it will fail over and over again (they really would need some euristic to auto-clean up even if it means that you're losing some data.)

The command to repair the database, really quick, is as follow:

nodetool scrub snap_websites files

Note that ...

Creating a new git repository

As I am now using git, I like to create my own repositories. In most cases the documentation is not that easy to follow. Here are the instructions I use.

First of all, I setup my own personal configuration (it can be used as a global setup for you). This is written in the ~/.getconfig and looks like this:

[user]
    name = AlexisWilke
    email = me@my-top-secret-email-address.com

[core]
    excludesfile = ~/.gitignore
[push]
    default = simple
[giggle]
    main-window-maximized = false
    main-window-geometry = 1114x789+144+184
    file-view-vpane-position = 389
    ...

Bad move for PHP unpack()! So unpack() stopped working?

Today I noticed many errors on one of my websites. Looking closer into it, I noticed that the code for the mo_references Drupal module stopped working.

It took me some time, especially because the code seemed to work just fine as all the files could easily be displayed.

Actually, that was not the case. The unpack() character 'a', which I used, was transformed from a simple string that gets trimmed, to all the characters, including the NULL characters. Ouch! Now we have to use the 'Z' character instead.

I use it to unpack() a tar file by loading 512 bytes of data in a ...

#PCDATA and DTDs

If you are like me and write DTDs to check your XML files to make sure you don't have too many mistakes in them, then you probably have had this problem before.

The #PCDATA has a very special behavior and it is really restrained as follow:

  • #PCDATA must appear at the start
  • #PCDATA must be repeated from zero to infinity, so only * work with it
  • #PCDATA cannot be used with sub-groups (things between parenthesis)

Something like this:

<!ELEMENT Z (P | (#PCDATA | A | B | C)* | Q)+>

does not work because you use + and #PCDATA is within a sub-group.

What you need ...

Why would Redirect and RedirectMatch in Apache2 not work?

As we are working on a new website, we had a problem where a redirect would not work. I tried both: a simple Redirect and a RedirectMatch as follow:

Redirect / http://finball.m2osw.com/
RedirectMatch permanent ^(.*)$ http://finball.m2osw.com$1

Both of these entries would not work at all.

I verified, to make sure, that the alias module was turned on. It was.

ls -l /var/apache2/mods-enabled

This did list the alias.conf and alias.load entries as expected.

So? What else?

Well... This was installed on a new server and we left the default entry in there:

ls -l ...

nvidia_XXX.ko No Such Device

Today I got a new video card because it looks like the old one I had was going bad. I hope that was not my KVM, although we'll see when it gets hot again, whether the video goes bouncy again or not... If not, then the old card is good for the trash (although it works in console mode just fine!)

So I got a new card. My old one was a NVidia GT 220. Fairly old model. Yes.

The new card is an NVidia GT 630 (to be precise: Asus GT630-SL-2GD3-L.)

When I tried to start X11, I saw an error (really quick) and the system did not come up. Looking closer into the matter, I could see that the NVidia ...

Why are my "vim: ..." commands not activated?

I use gVim all the time, I like that editor very much (emacs is just way too much, if you ask me.)

But once in a while I install a new server and by default they generally turn off the modeline feature. This is because there are potential security risks in link with that feature (i.e. vim starts running whatever script is defined in the text files that you edit...)

Anyway, I most often forget about the command to enable my:

vim: <setup>

(I most often define the tab stops, corresponding shift width and eventually the syntax of a file.)

Only, on those new servers, that doesn't ...

HP Printer options not offering "Color: Off" option anymore

As I upgraded to Ubuntu 13.10, I noticed that I lost the option to turn off the color when printing.

Looking around all the available options, no one to make it black and white (although the old option was saying something like: Color: Off; it was somewhat weird.)

Now that option is completely gone. There is no way for me to turn off my HP Printer color when I am in Acrobate or LibreOffice. I searched on the Internet to see whether that was just HP trying to get you to use colors on your printer or whether the option was available... somewhere else.

Indeed, I had to go to the System ...

My JavaScript code does not get the correct widget size, why?

As I am developing a set of pages for a customer, I ran in an intersting problem: my JavaScript function could not properly define the sizes of a box.

That box is heavily tweaked with the CSS assigned to it, as well as all of its neighbors. So I thought that may have something to do with it.

What I hadn't realized so far is that the ready() function of jQuery() is called once the script that includes it is ready (as in loaded) and not once the document as a whole is ready (done loading, i.e. onload event.)

With that knowledge it was easy to understand that I was actually finding myself ...

RJ45 and crossover cable

I got a cross over CAT6 cable and somehow the computers on which I used it do not like it... So I thought maybe it was not a valid crossover cable. Searching on the net I found a page with the following images which gave me the answer. You have to look for the colors of the wires in the RJ45. It's not very easy to see, but it is different enough (assuming you see colors...) that you should be able to tell exactly.

The easiest is simply to look for the "red" (orange) cable. If it is close to the edge in one RJ45 and far from the edge on the other, then you have a crossover ...

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