Configure grub bootloader

From Mandrivausers Wiki

GRUB stands for "GRand Unified Bootloader" and is one of the many bootloaders available for Linux and other OS's. One thing that must be noted about grub, is the device syntax. GRUB counts starting from zero. For example, hda is seen as (hd0). The partition hda1 would be seen as (hd0,0), hda2 as (hd0,1), hdb3 as (hd1,2), etc. Under Mandriva, the GRUB configuration file is "/boot/grub/menu.lst". Other distributions may use /etc/grub.conf or /boot/grub/grub.conf though.

Here's an example of a simple configuration

CODE
timeout 10
color black/cyan yellow/cyan
i18n (hd0,0)/boot/grub/messages
password linux
default 0
fallback 1
title linux
kernel (hd0,0)/boot/vmlinuz root=/dev/hda1 devfs=mount hdc=ide-scsi resume=/dev/hda2 splash=silent vga=788
initrd (hd0,0)/boot/initrd.img
title windows
root (hd0,1)
chainloader +1

Simple list of options:

   * timeout # 

The amount of time, in seconds, for the bootloader to wait before booting the default section.

   * color foreground/background/highlight 

Specifies what color to display the menu in. You can prefix blink- to foreground if you want a blinking foreground color.

   * i18n (partition /boot is located)/path/to/msg-file 

Specifies path to a text file that will display in the boot menu.

   * default # 

The default entry to boot. Note to start counting entries from zero, not 1. The default in the configuration would be "linux", which is called as "0'.

   * fallback # 

The entry to boot if the default entry fails.

   * title string 

The beginning line of a boot entry. String is what will display in the menu for that entry.

   * kernel (partition)/path/to/kernel kernel options 

This specifies the kernel image to boot from. kernel options is the line that is passed to the kernel at boot.

   * initrd (partition)/path/to/initrd 

The ramdisk image to load at boot.

   * root (partition) 

Specifies the root partition

   * chainloader +1 

Mechanism for loading unsupported operating systems by loading another boot loader. It is typically used for loading DOS or Windows.

   * password 

To specify a password for a lock function.

Examples:

CODE
title Mandrake
kernel (hd0,1)/boot/vmlinuz root=/dev/hda1 vga=788 devfs=mount hdc=ide-scsi splash=silent
initrd (hd0,1)/boot/initrd.img

This example will be labeled "Mandrake" and will load the kernel image (vmlinuz) and ramdisk (initrd.img) image from hda2. root=/dev/hda1" tells the kernel the "/" partition is /dev/hda1 (note it's not using the GRUB naming convention because GRUB does not use this, but only passes it to the kernel). "vga=788" tells the kernel what size Framebuffer to run. The rest are kernel specific options. In this example, devfs=mount to mount the devfs filesystem, hdc=ide-scsi tells hdc to use SCSI emulation (usually used for CD-burners), and splash=silent instructs bootsplash to hide the booting messages (other option is "verbose").

CODE
title Windows XP
root (hd0,0)
chainloader +1

This example will have an entry labeled "Windows XP" and will chainload off of hda1. Windows must be chainloaded so that it may boot itself.

[edit] Note on Security

Because of the way GRUB works, it can be easy for someone to pass bad or harmful options to the kernel during boot. To secure GRUB, a password entry can be used. Firstly, run the command "grub-md5-crypt" to generate an md5sum encryption of your password. For example, the password "linux" md5sum'd can be "$1$AUHMA0$lhDHRrJrV0kAkY7QQw0lW.", and would be entered into menu.lst like so...

CODE
password --md5 $1$AUHMA0$lhDHRrJrV0kAkY7QQw0lW.

The password entry could also be a non-encrypted password if you desire, by not appending the --md5

CODE
password linux

To make a boot entry require a password to boot, just insert "lock" after the title section. For example, say we want to lock windows from being loaded without a password.

CODE
title "Windows"
lock
root (hd0,0)
chainloader +1

There are many more options available for GRUB. Please refer to the GRUB Manual for more info on these options and features.