Andreas Bernauer's personal blog

I've recently stumbled across the following error message of Gnuplot:

illegal month

Gnuplot can handle time data. With set timefmt, you can specify the format of your time data. As of know, all your time data has to be in the same format, that is, all columns containing time data must have the same format.

Although every column used the same format, I still got this error message. Strangely enough, if I tested the plot command within gnuplot, the error message disappeared; only when I ran the script to plot the data the error message appeared.

Turns out that the reason for the error message is not a malformed data line, but a malformed command. In my case, I have used the wrong format for specifying the coordinates of set arrow, because I wrote the script with time data that had a different format. Changing the coordinates to adhere to the new time format made the error message disappear.

After upgrading to Ubuntu 10.04, vimperator could not read or write its .vimperatorrc anymore. Although all permissions were set correctly, the access to this file was denied. The access is also denied to firefox if you want to save a file as '.vimperatorrc'. Strangely, this is true for any file named '.XYZrc' in your home directory. The error message in the logs is

May 29 12:34:27 quick kernel: [ 7021.689247] type=1503 audit(1306665267.160:49):
operation="mknod" pid=4195 parent=1 profile="/usr/lib/firefox-3.6.17/firefox-*bin"
requested_mask="c::" denied_mask="c::" fsuid=1000 ouid=1000 name="/home/andreas/.vimperatorrc"

The access is denied by apparmor, in particular because of a rule in the privacy settings that disallows read or write access to *.rc files in the user's home directory. I don't know, why this broad apparmor rule is necessary, but I found a workaround for the .vimperatorrc problem. Reading the vimperator sources, I found that the configuration file is expected as '.vimperatorrc' (which causes the aforementioned problem) or '_vimperatorrc' (for Windows machines). It turns out that if on both GNU/Linux and Windows platforms one of the files does not exist, the other one is tried instead.

So, to let vimperator read its .vimperatorrc file, just rename .vimperatorrc to _vimpeatorrc. And keep in mind that firefox cannot read or write any file named *rc in your home directory (such as .my-vimperator.rc).

Alternatively you can disable apparmor (which I don't recommend) or update the apparmor rules (which I don't know how to do without removing the offending rule in the privacy profile as the manual page is incomplete here as far as I can see).

I've recently upgraded my system from Ubuntu 8.02 to 10.04 (Lucid Lynx). After the reboot, my wireless PCI card with Intersil Prism 2.5 Wavelan chipset (rev 01) did not work anymore.

First I thought the driver for this rather old card is missing. However, it turned out the interface was named wrong by the udev rules.

To fix the issue, I edited /etc/udev/rules.d/70-persistent-net.rules. There were two entries for my wireless card, one for the hostap_pci driver that named the interface wlan0 and one for the orinoco_pci driver that named the interface eth1. As eth1 showed up with ifconfig, but wlan0 did not, I figured orinoco_pci is working, but hostap_pci is not. So I changed the following lines in 70-persistent-net.rules from

# PCI device 0x1260:0x3873 (hostap_pci)
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:09:5b:11:e2:c9", 
    ATTR{type}=="1", KERNEL=="wlan*", NAME="wlan0"

# PCI device 0x1260:0x3873 (orinoco_pci)
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:09:5b:11:e2:c9", 
    ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="eth*", NAME="eth1"

to

# PCI device 0x1260:0x3873 (hostap_pci)
#SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:09:5b:11:e2:c9", 
    ATTR{type}=="1", KERNEL=="eth*", NAME="eth1"

# PCI device 0x1260:0x3873 (orinoco_pci)
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:09:5b:11:e2:c9", 
    ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="wlan*", NAME="wlan0"

That is, I commented out the section for hostap_pci and renamed the entry for orinoco_pci to use wlan0 as the interface name.

After a reboot, I could use my wireless network again.

Update: However, a new entry was added to the udev rules file so that after the next reboot, my wireless network card did not work anymore. The culprit was the udev rules generator file at /lib/udev/rules.d/75-persistent-net-generator.rules, which thought it still had to add a udev rule for the eth1 interface. I don't know how to debug udev rules, so the easiest way to fix this issue is to disable the rule generation once everything is set up nicely. For this, I added the following line at the beginning of the 75-persistent-net-generator.rules file, with the effect that no further rule generation for network cards happens:

GOTO="persistent_net_generator_end"

Of course, if you add or change your network cards, you should uncomment this new line to generate new rules.

Merry Grav-mass to you all!

Let's celebrate the birthday of Isaac Newton today, or even better, the ten days of Isaac Newton as suggested by Olivia Judson in the New York Times.

Thank you Richard Stallman for 25 years of free software. And for the GNU/Linux system. That is all.

I'm currently evaluating Zimbra as my webmail client. It looks pretty nice and even has keyboard shortcuts.

However, the listings available on the net seem to be outdated or not match with my configuration, so I copied the listing from the Preferences dialog and put them on a cheat sheet, that you can download here: Zimbra Keyboard Shortcuts (PDF).

I needed to plot data from a program in real-time for a demo, that is, as the program generates the data, I wanted it to show in some nice diagram.

A friend pointed me to Visualize real-time data streams with Gnuplot by Thanassis Tsiodras, which is very nice: you specify the number of streams to plot and where to plot them, and feed it with lines like '0:1.23', '1:2.3', etc. defining the data points for the individual streams (here: first point on stream 0 is 1.23, first point on stream 1 is 2.3, etc.).

However, I needed to plot several streams in a single window, which that version lacked. So I extended that program with the ability to plot several streams into a single window (download).

For this, you specify both the number of streams you want to plot and the number of windows you want to show. Furthermore, you specify in which window each stream is plotted. I kept as much as possible of the original command line interface to ease the transition to this new version. The result looks like this:

Who's designing the error messages of g++? Anyways, here is a translation:

error: request for member ‘foo’ in ‘((Test*)this)->Test::_bar’, 
which is of non-class type ‘C_bar*’

means: in class Test, you've written _bar.foo, but _bar is a pointer; you need to write _bar->foo, that is, change the dot to an arrow.

Happy C++ coding!

I just stumbled over my python code, similar to the following one, which raises an UnboundLocalError in the first line of push:

def func_stack1():
    stack = []
    def push(num):
        print "stack before: ", stack
        stack = stack + [num]
        print "stack after: ", stack
    return push

push = func_stack1()
push(1)

I've just updated the documentation of SystemC 2.2.0. It includes more graphs, the source code of the .cpp files, and I turned the comments of some functions to doxygen comments which now show up in the docs. I plan to update the docs with more documented functions (the original source contains only simple comments instead of doxygen comments).

I wanted to 'upgrade' my python from 2.5 to 2.6 on Ubuntu. Unfortunately, I could not find .deb packages for Ubuntu. Fortunately, the Python 2.6 sources (sig) are available, so I can compile it from source. Here's what I had to do to get it running. (Short version: apt-get build-dep python2.5 and apply this patch to disable unavailable and outdated modules.)

I gvim, if you set

:setlocal spell spelllang=en_us

gvim will spell-check your file and underline wrongly spelled words with a red line much like you know it from OpenOffice. If you

:set mousemodel=popup

you can even right click on any misspelled word to get a list of suggested corrections.

However, this sometimes did not work for me. I could not figure out a reason, until I read the help docs again, which clearly say:

Note for GTK: don't release the right mouse button until the menu appears, 
otherwise it won't work.

They actually mean what they say: if I release the right mouse button too fast, the menu appears, but it does not replace the misspelled word with the corrected word. Only if keep the right mouse pressed until the menu appears, it works, for whatever reason. RTFM!

There's an interesting discussion at slashdot over an article in The Guardian concerning the effectiveness of CCTV cameras. In short, The Guardian cites a police man that only 3% of street robberies were solved using CCTV images.

While this seems to argue against installation of CCTV cameras, there are several interesting points brought up in the discussion on slashdot, though.

• Concerning the 3% figure, noa points out that it does not say anything about how much crime the cameras prevented, the reason why they were installed in the first place.

• The basis for CCTV cameras is law enforcement, so mi asks whether we want 100% law enforcement to which ShieldW0lf answers yes, but only if 99% of the laws are abolished. mi also points out that cameras can help protect citizens against police violience, as happened in Philadelphia.

• On the other hand, Wowsers reports that a camera could not help find a guy assaulting a woman, because the camera was used to catch motorists using the wrong lane, presumably because this gives money to the city.

• Even worse, the cameras are sometimes used for spying, as Toreo asesino reports. He was making out with a girl in a park and observed a camera being pointed to him.

Thank you, slashdot, for your great discussion system. On a personal note, I don't think CCTV is a cure for everything. It may help in some cases (say banks), but most often it will only invade people's privacy and satisfy the curiosity of some (unknown) security people while pushing crime to other, non-monitored areas. More intelligent software, as the Guardian article suggests, won't help here.

If you link a static library to your executable, the GNU linker ld (as many others) only adds those symbols that ld thinks are actually used in your executable (that's a feature). Unfortunately, ld can only check if the symbol is in use, but not if the side effects of the symbol's initialization is used. Thus, your program will fail if it depends on the initialization of an unused static object.

In my case, I have a factory (class module::factory<T> : public factory_plant {...} factory;) at which classes can register themselves with a name (module::factory<Group> f("Group")). If I call the factory with a name (factory.create("Group")), the factory returns a pointer to a newly created class associated with that name. The class registers itself via a static object (here: f) whose initialization code does the actual registration.

The problem arises if the class is not used directly and the linker throws the static object away. The registration does not happen and thus I can't use the factory to create an object of the class. There are several possibilities to work around this feature:

Use --whole-archive to tell the linker to include all symbols, no matter what (with gcc use -Wl,--whole-archive -lmylib -Wl,--no-whole-archive). The drawback is that symbols that I neither use nor care about are also included, resulting in increased code size.

Use -u<symbol> to tell the linker to treat <symbol> as if undefined and thus include it in the executable, even it is not used. The drawback here is to know what <symbol> looks like. Easy for C files, difficult (and not portable) for C++ files (see Name mangling in Wikipedia).

Use static initializers (thanks to Alex for this). This is my preferred method. I use a throw-away class, which I add to the header file:

static struct Init {
     Init() {
          static module::factory<Group> init("Group");
     }
} init;

Johnny Lee strikes again. After using the Wii remote to create a low cost multi-touch whiteboard he uses the Wii remote to implement head tracking and 3D virtual reality. He coupled the Wii remote with a PC and a monitor which displays the 3D world. Thanks to the 3D processors in our brain (and the normal processors in Lees computer), we get an impressive illusion of three dimensionality with objects sticking out of the TV. You can even look into a football stadium as if you look through a window: lean to the right and you see more of the field, lean to the left and you see more of the audience.

However, it works only for a single person (and I guess you need a pretty big TV screen such as the one Lee owns to enjoy this 3D experience. ) Great work!