Start an installation from GRUB

1. Description

This tip will show you how to start an installation for network or hard disk from an existing GRUB bootloader from CentOS or another distro. This is useful if the system has no CD or DVD bootable device and it is not possible or convenient to boot from other removable media. The example uses CentOS 5 i386 but should work for other versions and architectures.

2. Fetch boot kernel and initrd

The required installer vmlinux and initrd.img files can be gotten from loopback mount of an ISO image, from a close by mirror, or from an installation tree on hard disk. The example shows fetching them from centos.org:

cd /boot
wget http://mirror.centos.org/centos/5/os/i386/isolinux/vmlinuz
mv vmlinuz vmlinuz-c5
wget http://mirror.centos.org/centos/5/os/i386/isolinux/initrd.img
mv initrd.img initrd-c5.img

3. Create GRUB boot stanza

The following assumes that /dev/sda1 (or /dev/hda1 - first partition on first disk) is the boot partition. For /dev/sdb3 substitute (hd1,2) for (hd0,0), etc.

title CentOS 5 Install
    root (hd0,0)
    kernel /vmlinuz-c5 ro
    initrd /initrd-c5.img

If there is no /boot partition and the root filesystem is on the first partition use

title CentOS 5 Install
    root (hd0,0)
    kernel /boot/vmlinuz-c5 ro
    initrd /boot/initrd-c5.img

Optional parameters can be added to the kernel. For example

title CentOS 5 Install
    root (hd0,0)
    kernel /vmlinuz-c5 ro keymap=no lang=en_US.UTF-8 method=http://10.0.0.10/repos/CentOS/5.5/os/i386
    initrd /initrd-c5.img

Or

title CentOS 5 Install
    root (hd0,0)
    kernel /vmlinuz-c5 ro vnc vncconnect=192.168.15.2 ip=dhcp upgradeany lang=en_US keymap=us method=http://192.168.15.40/mrepo/centos5-x86_64/disc1/ ksdevice=link
    initrd /initrd-c5.img