When in college, I would often ssh to the computer in the lab. I always prefer to use screen (the ability to detach sessions is too good to resist!). But, what happens when you have screen running on both – the local and remote machines? Any commands (eg, ctrl-a c) would result in the action happening on the local instance of screen. Even if one changes the key-bindings in the remote machine, things do not improve much.

The work-around is to use a sequence of ‘a’. For instance, to open a new screen on the remote machine, you will have to do the following key sequence -
ctrl-a a c

Similarly, for a screen inside a screen inside a screen, you will have to do a sequence of a’s – ctrl-a a a a … (i times) c

Hope it works fine for you. You can find more about the extension here.

Anyway, although the project does come with some python wrappers, I was a little impatient to figure out how to use them. Also, the wrappers and all the other programs that use it always use it in the .lib format. Now, although I have no problem as such with using it as a library, I found it very difficult to port it (to the BeagleBoard). Anyway, to cut a long story short, I am now trying to get it working on the BeagleBoard.

Also, I’m trying to write some Python bindings that use the source code to decode and encode the data matrix. Hopefully I’ll be releasing the code (the meagre amount I wrote) out soon. Looking forward to it…

One of the nice things I found on Windows is using RocketDock. This software basically makes your desktop look something like this -

The first thing I did was hid all my Desktop items (including recycle bin). There are plenty of sites on the net which tell you in detail how to do this. Just google for something like “hide desktop itsems” or something similar, and you will surely find it.

Recently, I wanted to empty my recycle bin. But, however hard I tried, I just could not find the trash can of my computer. Finally, I found a site that taught me how to. Although I have no clue as to why this works, but it does – I tried it!

Go to Start –> Run –> type “::{645FF040-5081-101B-9F08-00AA002F954E}” (without quotes, of course!) and you should have your recycle bin open..

To switch off your screen from the command line, just give the following command in the terminal -

xset dpms force off

In fact, an even more convenient thing is, just convert this to a script by adding the following to the file ~/.gnome2/gnome-scripts/<name_of_script> -

!#/bin/bash
xset dpms force off

Do remember to change the permission of the script (chmod a+x  /.gnome2/nautilus-scripts/<name_of_script>)

I found this quite useful. Hope you do too. Will write up something more about xset soon.

~$sudo apt-get install build-essential

With the webcam being such an integral part of our day-to-day lives, there lies this desire to fiddle around, grab images, and let your imagination wild! A little help from google, and one can find a plethora of examples. However, for all these examples, you will need to install opencv.

The first way (and the most simplest of all) is to let your package manager handle the mess. Unlike this blog, I found this method second (or else, I would not have struggled to compile it myself!).
First, we search for the packages that contain opencv or are required by opencv.

~$sudo apt-cache search opencv
libcv-dev – development files for libcv
libcv1 – computer vision library
libcvaux-dev – development files for libcvaux
libcvaux1 – computer vision extension library
libhighgui-dev – development files for libhighgui
libhighgui1 – computer vision GUI library
opencv-doc – OpenCV documentation and examples
python-opencv – Python bindings for the computer vision library

The list is all the files we need to download. The following command will do the needful -

~$sudo apt-get install libcv-dev libcv1 libcvaux-dev libcvaux1 libhighgui-dev libhighgui1 opencv-doc python-opencv

Now, for those who want to do it the hard way! I found this solution on OpenCV Installation Guide.

1. Download tarball and extract the files

$~cd <path_to_directory>
$~wget http://sourceforge.net/projects/opencvlibrary/files/opencv-linux/1.1pre1/opencv-1.1pre1.tar.gz/download
$~tar -xvvzf <downloaded_tarball>
$~cd

2. To run the configure script successfully, we need the development lib for gtk2.0. If this is not installed on your computer, it will compile the library without any UI support. I’m not sure how to run it without the UI support, so I took the easier way out – I installed it! Thus, along with the gtk runtime, we need to install the development library.

~$sudo apt-get install libgtk2.0-dev
~$sudo apt-get install libavformat-dev

3. To install, give following commands
~$./configure –prefix=/usr/local –with-python –with-swig
~$ make
~$sudo make install
~$sudo ldconfig

4. To check the installation

~$make check
~$cd sources/c/
~$./build_all.sh
~$./laplace (or any other of the executables)

The only thing is, one has to be a little careful about the libraries, as they will not be in the usual /usr/include/lib, but in the opencv folder itself. Check the sample files and the build file to see how to use the libraries.

Note : Must try this for vector linux too..

Initial xterm - black on white

Although this will not change the functioning of your computer or provide you with some cool new application, one thing is will definitely do is brighten your mood!

More often than not (as was with the case with me), modifying xterm to suit one’s preferences is not really a necessity. But yet, nothing is more pleasing than working on an xterm with colours of your choice. Unfortunately, the man pages tend to delve into way more details than one wants to handle, and invariably one lands up using the default setting. After multiple (failed) attempts to go through the man pages, and then searching some websites, this was one method that worked for me.

The settings that describe how your xterm looks are stored in the file ~/.Xresources. Inititally, my Ubuntu and Vector Linux did not have this file in the home directory (and were running on the system defaults).

Here is a copy of my .Xresources file -

~$vim .Xresources
xterm*font: -*-fixed-medium-r-*-*-18-*-*-*-*-*-iso8859-*
xterm*font1: -*-*-*-*-*-*-2-*-*-*-*-*-*-*
xterm*font2: -misc-fixed-*-r-normal-*-8-*-*-*-*-*-iso8859-*
xterm*font3: -b&h-lucidatypewriter-bold-*-*-*-12-*-*-*-*-*-*-*
xterm*font4: -*-screen-bold-r-normal-*-16-*-*-*-*-*-iso8859-*
xterm*font5: -*-lucidatypewriter-medium-*-*-*-18-*-*-*-*-*-*-*
xterm*font6: -*-lucidatypewriter-medium-*-*-*-20-*-*-*-*-*-*-*
xterm*font7: -dec-terminal-bold-r-normal-*-14-*-*-*-*-*-iso8859-*
XTerm*background: black
XTerm*foreground: green
XTerm*pointerColor: red
XTerm*pointerColorBackground: black
XTerm*cursorColor: navy
XTerm*internalBorder: 3
XTerm*loginShell: true
XTerm*scrollBar: false
XTerm*scrollKey: true
XTerm*saveLines: 1000
XTerm*multiClickTime: 250

One can change the parameters to modify xterm the way one wants. After modifying the file, to load the changes, one must perform -

~$ xrdb -merge .Xresources

This is a quick-fix solution really, and does not really understand all the parameters involved in xterm. I intend to figure it out in more detail in the time to come..

new xterm - green on black

A very useful chart to have pinned to the board at your workstation

Vim is one of the sweetest text editors I’ve come across. It’s not only extremely simple (once you get the hand of it), but extremely convenient for anyone who enjoys using the terminal. Above is a cheat sheet which (I find) makes life particularly easy.

Also, a great place to start vimming is this tutorial.

Now, installing Hardy is quite easy, if you have a fully-working cd-drive or good net connection. Unfortunately, I have neither. I do not have an option of a ‘boot from USB’. And, for a long time, my laptop lay dead, somewhere at the back of my cupboard. In a final attempt to get it working again, I thought of using an approach similar to the one used to install Vector Linux – installing it directly from the iso!

Since my drive was not fully working, it meant that it was not fully disfunctional either. The cd drive refused to work for long stretches of time, implying that installing anything from a cd was impossible. However, booting from the Live CD could still happen on a good day. And so, that is where we start.

Boot from the Live CD and open the disk partitioner. You will need to make the following partitions right away -
1. Boot partition (sda1, ~150MB)
2. Partition to store the iso (sda2, ~750mb)
3. Rest of the drive
We will partition the ‘rest of the drive’ during the installation of Ubuntu.

Perform the following commands from the terminal :

~$ mkdir /tmp/install_cd
~$ sudo mount disk-image.iso -o loop /tmp/install_cd
~$ sudo mkdir /mnt/installer
~$ sudo mount /dev/sda2 /mnt/installer
~$ sudo cp -r /tmp/install_cd/* /mnt/installer
~$ sudo cp -r /tmp/install_cd/.disk /mnt/installer
~$ sudo umount /tmp/install_cd

What the above does is it creates an image of the cd on the drive sda2. Hence, when the computer starts and grub is looking for a place to start the boot, it is guided to this drive.

Finally, we need to install grub (on our boot partition). To install grub, we first mount the drive sda1 to some temporary directory and then install grub.

~$ mkdir tmp_grub
~$ sudo mount /dev/sda1 tmp_grub
~$ sudo grub-install /dev/sda –root-directory=tmp_grub/

Now, using your favourite text editor, create/edit the file tmp_grub/boot/grub/menu.lst and add the following :

title Ubuntu Installer
root (hd0,0)
kernel /casper/vmlinuz boot=casper root=/dev/ram ramdisk_size=1048576 rw
initrd /casper/initrd.gz

That’s it! Now, restart your computer and watch as the installation unfurls..

The other day, my friend was in quite a quandary. The situation was simple. He tried to log in as the super-user (with the ‘su’ command), but the computer just did not accept the password. Here is the explanation I gave him -

‘su‘ is the super-user himself. You can set the su password by the following steps -

1. System –> Administration –> Users and Group
2. Click unlock, and type in your user password
3. Select ‘root’ (double click on it once) and a window containing its properties will open.
4. In the Password section in the Accounts tab, choose set password by hand and select a password.
5. Close the window (click on close on the right bottom)

Now, if you open a terminal window and type su, it will prompt you for password. Type in the root password that you just entered and all will be well!

The super-user is the ‘god’ of your computer, so whatever He says, happens (that’s why as root, you never have to type sudo before a command).
You are a normal user, but you have a magic powers (ie superuser privileges) that gives you the right to play god. But, this power is not available to you all the time. You can only use it when you wave your magic wand (ie the ‘sudo’ command).

I hope it makes sense!