\begin{exe} {Recovering from a Corrupted  GRUB Configuration}

   \begin{enumerate}
      \item
      Edit your \textbf{GRUB} configuration file
      (\filelink{/boot/grub/grub.cfg},
      \filelink{/boot/grub2/grub.cfg} or
      \filelink{/boot/grub/grub.conf}), and modify the
      \texttt{kernel} line by removing the first character
      of the value in the field named \texttt{UUID}. Take
      note of which character you removed, you will replace
      it in rescue mode. (If your root filesystem is
      identified by either label or hard disk device node,
      make an analogous simple change.)  Keep a backup copy
      of the original.
      \begin{info}[On a BLSCFG System]
         You can corrupt the command line by editing
         \filelink{/etc/grub2/grubenv} instead.
      \end{info}
      \item
      Reboot the machine. The system will fail to boot,
      saying something like \verb?No root device?  was
      found. You will also see that a \verb?panic? occurred.
      \item
      Insert into your machine the \textbf{installation} or
      \textbf{Live} \textbf{DVD} or \textbf{CD} or
      \textbf{USB} drive (or network boot media) if you have
      access to a functioning installation server).  Reboot
      again.  When the boot menu appears, choose to enter
      rescue mode.
      \item
      As an alternative, you can try selecting a rescue image
      from the \textbf{GRUB} menu; most distributions offer
      this.  You'll get the same experience as using rescue
      media, but it will not always work.  For example, if
      the root filesystem is damaged it will be impossible
      to do anything.

      \item

      In rescue mode, agree when asked to search for
      filesystems.  If prompted, open a shell, and explore
      the rescue system by running utilities such as
      \textbf{mount} and \textbf{ps}.
      \item
      Repair your broken system by fixing your \textbf{GRUB}
      configuration file, either by editing it or restoring
      from a backup copy.
      \item
      Type \verb?exit? to return to the installer, remove
      the boot media, and follow the instructions on how to
      reboot.  Reboot your machine.  It should come up
      normally.
   \end{enumerate}
\end{exe}

