I want to print this text :

make -j 5 KDEB_PKGVERSION=1.yourcustomname deb-pkg

But I feel because of the underscore , LaTeX generates an error missing $ inserted and it doesn't print it as well.

Secondly, In the fbox{} , I wanted to print the two texts on the next line(i.e) one text per line , so I used and even par but it doesn't seem to work and I would like to align the (or) as well.

 fbox{texttt{uname -a}\(or) texttt{cat /proc/version}}

Here is my full source code:

documentclass[12pt]{article}

author{Subham Soni S.}

date{today}

title{Compiling and Installing a Kernel 3.13.3 On Ubuntu, Debian and its Derivatives}

begin{document}

maketitle

To replace the existing textsl{kernel} with a new one, do the following:

begin{enumerate}

item Create a folder named emph{kernel} in the home directory.

item Download the latest kernel to the folder from  texttt{www.kernel.org}.

item Extract the file.

item In the terminal, type the following command to textbf{install the neccesary tools to compile the kernel}:

  begin{center}

    fbox{texttt{sudo apt-get install gcc libncurses5-dev dpkg-dev}}

  end{center}

item Enter the directory of the extracted kernel source

  begin{center}

    fbox{texttt{cd kernel} par texttt{cd linux-3.13.3}}

  end{center}

item Configure the kernel

  begin{center}

    fbox{texttt{make menuconfig}}

  end{center}

  In this menu you can customize your kernel

item Save and exit

item Compile the kernel

  begin{center}

    fbox{texttt{make -j 5 KDEB_PKGVERSION=1.yourcustomname deb-pkg}}

  end{center}

  emph{This process might take a while...}

item Install the kernel

  begin{center}

    fbox{texttt{sudo dpkg -i ../linux*.deb}}

  end{center}

item Reboot

  begin{center}

    fbox{texttt{sudo reboot}}

  end{center}

item Run the following commands to check the kernel version

  begin{center}

    fbox{texttt{uname -a}\(or) texttt{cat /proc/version}}

  end{center}

item You can easily uninstall the kernel with the command:

  begin{center}

    fbox{texttt{sudo apt-get purge linux-image-3.13.3 linux-image-3.13.3-dbg}}

  end{center}

end{enumerate}

end{document}

Let us be colorful with tcolorbox:

documentclass{article}

usepackage{listings}

lstdefinestyle{mystyle}{%

    basicstyle=smallttfamily,

    breaklines=true,

    columns=fullflexible,

}%



usepackage{tcolorbox}

tcbuselibrary{most}

newtcblisting{session}{%

      width=linewidth,

      arc=3pt,

      top=-2mm,

      bottom=-2mm,

      left=0mm,

      right=0mm,

      boxsep=1mm,

      boxrule=1pt,

      colback=blue!20!green!20!white,

      listing only,

      listing options={style=mystyle},

      breakable,

}%



begin{document}



author{Subham Soni S.}

date{today}

title{Compiling and Installing a Kernel 3.13.3 On Ubuntu, Debian and its Derivatives}

maketitle



To replace the existing textsl{kernel} with a new one, do the following:

begin{enumerate}

item Create a folder named emph{kernel} in the home directory.



item Download the latest kernel to the folder from  texttt{www.kernel.org}.



item Extract the file.



item In the terminal, type the following command to textbf{install the necessary

tools to compile the kernel}:

begin{session}

sudo apt-get install gcc libncurses5-dev dpkg-dev

end{session}



item Enter the directory of the extracted kernel source

begin{session}

cd kernel

cd linux-3.13.3

end{session}



item Configure the kernel

begin{session}

make menuconfig

end{session}

In this menu you can customize your kernel



item Save and exit



item Compile the kernel

begin{session}

make -j 5 KDEB_PKGVERSION=1.yourcustomname deb-pkg

end{session}

emph{This process might take a while dots}



item Install the kernel

begin{session}

sudo dpkg -i ../linux*.deb

end{session}



item Reboot

begin{session}

sudo reboot

end{session}



item Run the following commands to check the kernel version

begin{session}

uname -a

cat /proc/version

end{session}



item You can easily uninstall the kernel with the command:

begin{session}

sudo apt-get purge linux-image-3.13.3 linux-image-3.13.3-dbg

end{session}

end{enumerate}

end{document}

The problem is in the row 28, word KDEB_PKGVERSION. If you write KDEB_PKGVERSION file works.

documentclass[12pt]{article}

author{Subham Soni S.}

date{today}

title{Compiling and Installing a Kernel 3.13.3 On Ubuntu, Debian and its Derivatives}

begin{document}

maketitle

To replace the existing textsl{kernel} with a new one, do the following:

begin{enumerate}

item Create a folder named emph{kernel} in the home directory.

item Download the latest kernel to the folder from  texttt{www.kernel.org}.

item Extract the file.

item In the terminal, type the following command to textbf{install the neccesary tools to compile the kernel}:

  begin{center}

    fbox{texttt{sudo apt-get install gcc libncurses5-dev dpkg-dev}}

  end{center}

item Enter the directory of the extracted kernel source

  begin{center}

    fbox{texttt{cd kernel} par texttt{cd linux-3.13.3}}

  end{center}

item Configure the kernel

  begin{center}

    fbox{texttt{make menuconfig}}

  end{center}

  In this menu you can customize your kernel

item Save and exit

item Compile the kernel

  begin{center}

    fbox{texttt{make -j 5 KDEB_PKGVERSION=1.yourcustomname deb-pkg}}

  end{center}

  emph{This process might take a while...}

item Install the kernel

  begin{center}

    fbox{texttt{sudo dpkg -i ../linux*.deb}}

  end{center}

item Reboot

  begin{center}

    fbox{texttt{sudo reboot}}

  end{center}

item Run the following commands to check the kernel version

  begin{center}

    fbox{texttt{uname -a}}par

    or fbox{texttt{cat /proc/version}}

  end{center}

item You can easily uninstall the kernel with the command:

  begin{center}

    fbox{texttt{sudo apt-get purge linux-image-3.13.3 linux-image-3.13.3-dbg}}

  end{center}

end{enumerate}

end{document}

EDIT:

with the comand

fbox{texttt{uname -a}}par

or fbox{texttt{cat /proc/version}}

you have two lines in two box

You can try with fancyvrb that also allows for friendlier input:

documentclass{article}



usepackage{fancyvrb}

DefineVerbatimEnvironment{session}{Verbatim}{frame=single,fontsize=small}



begin{document}



author{Subham Soni S.}

date{today}

title{Compiling and Installing a Kernel 3.13.3 On Ubuntu, Debian and its Derivatives}

maketitle



To replace the existing textsl{kernel} with a new one, do the following:

begin{enumerate}

item Create a folder named emph{kernel} in the home directory.



item Download the latest kernel to the folder from  texttt{www.kernel.org}.



item Extract the file.



item In the terminal, type the following command to textbf{install the necessary

tools to compile the kernel}:

begin{session}

sudo apt-get install gcc libncurses5-dev dpkg-dev

end{session}



item Enter the directory of the extracted kernel source

begin{session}

cd kernel

cd linux-3.13.3

end{session}



item Configure the kernel

begin{session}

make menuconfig

end{session}

In this menu you can customize your kernel



item Save and exit



item Compile the kernel

begin{session}

make -j 5 KDEB_PKGVERSION=1.yourcustomname deb-pkg

end{session}

emph{This process might take a while dots}



item Install the kernel

begin{session}

sudo dpkg -i ../linux*.deb

end{session}



item Reboot

begin{session}

sudo reboot

end{session}



item Run the following commands to check the kernel version

begin{session}

uname -a

cat /proc/version

end{session}



item You can easily uninstall the kernel with the command:

begin{session}

sudo apt-get purge linux-image-3.13.3 linux-image-3.13.3-dbg

end{session}

end{enumerate}

end{document}

Here's a partial picture: