Today I was bitten by the bug to see the source code of the command "ls" in GNU / Linux. This command belongs to the "coreutils" package so to obtain it you had to execute
apt-get source coreutils
The error thrown in Linux Mint was
E: Unable to find a source package for coreutils
The problem in Linux Mint, is that they do not add the repositories that contain the source codes from which the packages we installed were compiled.
The solution is simple, we just have to add the repositories to the sources.list
sudo pluma /etc/apt/sources.list
Now for each repository "deb" we have to add its counterpart "deb-src" which would be the repository of the source code
For example if we have the repository
deb http://packages.linuxmint.com/
We add its counterpart
deb-src http://packages.linuxmint.com/
And so with all repositories, or at least of which we want to be able to receive the source code
We update
sudo apt-get update
And now if we can get the source code of the desired package
Here is the code for `ls` -> http://git.savannah.gnu.org/gitweb/?p=coreutils.git;a=blob_plain;f=src/ls.c;hb=HEAD