sources.list file in Ubuntu

This is something I got to know recently while trying to install a new software package on Ubuntu. 

In Ubuntu, we use apt-get command line tool very often. It is, Ubuntu's Advanced Packaging Tool (apt) which performs functions such as installation of new software packages, upgrade of existing software packages, updating of the package list index, and even upgrading the entire Ubuntu system. 

sources.list file located in /etc/apt folder, is the default file which contains the details about the repositories needed when installing or upgrading the applications. When the system needs to know from where it may download the related stuff to install/upgrade it basically goes through this file.  

Repositories are servers which contain sets of packages. Ubuntu uses apt for package management. apt stores a list of repositories or software channels in this file. 

We can add a new repositories by simply adding a new line to this file. You can learn about the format of the entries in this file here. 

Once the editing stuff done, we have to do one more thing. Just to make apt aware of the changes done to sources.list, run;

sudo apt-get update

You can read further in Ubuntu help page.

"Boot-Repair" - Grub installer GUI application

I've recently installed Ubuntu 11.10 along with Windows 7. After installing Ubuntu when the machine restarted, it simply started with windows 7 just as I haven't installed any other OS.

But somewhat different from before, it showed an error saying, "MBR error 3".
And when I searched here and there, I was able to find out there's nothing wrong with Ubuntu installation.  The problem is the grub has not installed properly. So I had to reinstall the grub.

I was able to find a really cool application called "Boot-Repair". Here is how to use it and re-install grub just in few minutes.

First you need to boot Ubuntu from a Live CD. Then you have to install this "Boot-Repair" application. For that, simply enter the following commands one after the other (in a terminal).

sudo add-apt-repository ppa:yannubuntu/boot-repair
sudo apt-get update
sudo apt-get install boot-repair

This will install "Boot-Repair" application, so then you can re-intall grub just by one click. :)

Load the application and you will see an option there to re-install grub. This will repair the above error. When you restart, you will be prompted to choose the OS as you expected.

If you still want to do this manually you can do it as it is in this Ubuntu forum.
http://ubuntuforums.org/showthread.php?t=1893219