Reinstall CentOS using grub

This post is here mainly because I always forget how to do it. This is one of the simplest ways to reinstall a Centos (will probably work for RHEL and maybe even Fedora) system without needing PXE or physical access to the machine. Make sure that that you have tested you kickstart before you use it and don’t blame me if anything goes wrong.

Save the following script and make it executable then run it. It will ask some questions about networking and hostname and then write a new grub stanza to you grub.conf. It will also download the correct kernel and initrd from the information you have given it and put them in the correct position for grub to find them when it boots.

When you reboot you should be able to select Kickstart Centos and it will boot off the new kernels and pull down the kickstart then reinstall.

#!/bin/bash -x

echo -n "Enter kickstart url: "
read -e ksurl

echo -n "Enter Hostname: "
read -e hostname
echo -n "Enter IP Address: "
read -e ipaddr
echo -n "Enter Gateway: "
read -e gateway
echo -n "Enter Netmask: "
read -e netmask
echo -n "Enter Nameservers: "
read -e nameservers

repourl=$(curl $ksurl 2>/dev/null | sed -n 's/^url.*\(http\)/\1/ p')
#echo $repourl
vmlinuz_url="${repourl}/isolinux/vmlinuz"
initrd_url="${repourl}/isolinux/initrd.img"

date_now=$(date +%Y%m%d%H%M%S)

grub_stanza="
title Kickstart Centos 5 ${date_now}
        root (hd0,0)
        kernel /reinstall/vmlinuz ksdevice=eth0 load_ramdisk=1 prompt_ramdisk=0 ramdisk_size=16384 serial hostname=${hostname} ip=${ipaddr} gateway=${gateway} netmask=${netmask} dns=${nameservers} noipv6 ks=${ksurl}
        initrd /reinstall/initrd.img
"

echo "$grub_stanza"

echo -n "Please check the grub stanza above and enter 'y' if it is correct: "
read -e confirmed

if [ $confirmed == 'y' ]; then
        echo "Downloading kernel and initrd..."
        mkdir -p /boot/reinstall
        (cd /boot/reinstall/;/usr/bin/urlgrabber $vmlinuz_url )
        (cd /boot/reinstall/;/usr/bin/urlgrabber $initrd_url )
        cp /boot/grub/grub.conf /boot/grub/grub.conf.bak_`date +%Y%m%d%H%M%S`
        echo "$grub_stanza" >> /etc/grub.conf
fi