take five

Have you ever found yourself with a non-booting GNU/Linux box?
 
If the cause is a corrupted grub installation (by a bad move on kernel upgrade, a Windows update or whatever) all you have to do is simply:
 

• set the BIOS of your machine to have CD/DVD-rom player as the 1st boot device; 
• insert the Fedora/CentOS/RHEL media on it and boot the system, 
• choose {or manually insert}: linux rescue and press return, 
• a number of messages will be displayed until you will be taken to a working shell and your old system is mounted on /mnt/sysimage path, 
• give 'chroot /mnt/sysimage' command to "phisically translate" the shell on your original installation 
• 'cd /boot/grub' 
• then check where grub results installed if you have different disks on your machine with a grep '#boot' grub.conf 
• read the output, verify it's correct eventually with the help of an fdisk -l command, 
• now you are ready to install grub, after you've choosen the device (or partition) where it sould is located give the command grub-install /dev/device-choosen {ie that could be /dev/sda} 
• now close the shell and reboot, the system should be working correctly now!