Lilo, Grub and boot loaders

                    Lilo is the Linux bootstrap loader used by the Red Hat distribution up to and including version 7.1. Red Hat version 7.2 defaults to the use of Grub as the default boot loader. Grub supports a password that controls access to a Grub shell.

Lilo and Grub are the Linux bootstrap loaders that actually loads and starts the kernel. Only one bootloader, Lilo or GRUB, is used. The Linux install will ask if you want to place lilo (or Grub) on the master boot record (MBR). The answer of course is YES (Unless you are installing Windows NT/2000. See special install section for dual booting with these operating systems). If you do not install Lilo (or Grub) on the MBR, you can boot Linux from a boot floppy which can be generated during the install.

Other bootstrap loaders are available. A DOS program called loadlin can boot Linux from DOS. Loadlin can be found on the Red Hat CD under CDROM:\dosutils\. Both loadlin.exe and the Linux kernel must be loaded on a DOS partition. A commercially available software product "System Commander" from V Communications requires and partially installs in a DOS partition. See: VCOM: System commander product information

SCSI and lilo: The choice of selecting "Use Linear Mode" during lilo install is a little complicated. PCs running Microsoft operating systems use a SCSI BIOS based LBA mode to access drives of more than 1,024 MB. This is the default selection for most PCs. Check your SCSI BIOS if you are un-sure.
RH 5.2: Use the Linux default lilo setting of [*] "Use Linear Mode" .
RH 6.0: The default was changed to [ ] where Linear mode is un-selected. This is incompatible with most Microsoft OS's. If you are dual booting with Windows, you will probably want to set to [*] "Use Linear Mode" .
RH 6.2/7.1: The default "Use Linear Mode" is pre-selected. This is compatible with LBA mode. (It implies LBA mode).

[Potential Pitfall]: If the system boots to a prompt "LI" and a blinking cursor and is stuck, you chose the wrong option for your SCSI configuration.

Systems using Unixware or older PCs with smaller drives may NOT be using LBA and thus Use Linear Mode must be unselected. If this selection is incorrect, your machine will not boot and the Master Boot Record will have to be restored and lilo will have to be re-installed.

Adaptec SCSI card users: Press ctrl-A on boot up to enter the SCSI card BIOS set-up. This is where you chose LBA mode or not. ( > 1 Gb addressing)

[Potential Pitfall]: Adding an extra drive on which to install Linux: If the drive is a pre-formatted drive for Microsoft Windows, and if you boot Windows after installing the drive you may experience the following problem. Windows will recognize and assign a letter to the new drive and may re-assign the letters assigned to your CD-ROM and previous drives. If installing a new pre-formatted drive, DO NOT boot to Windows. It would be best to boot from the Linux CD-ROM. The Linux install will allow you to assign the new drive as a Linux drive. Thus when booted to Windows (after the Linux install), the system will not recognize the new Linux drive and therefore will not reassign your drive letters.

Pitfall Fix: If you do reboot to Windows and Windows re-assigns your drive letters for your CD-ROM, restore the settings by:

• "Start" + "Settings" + "Control Panel"
• Select "System"
• Select the tab "Device Manager" and select the CD-ROM
• Set the drive letter to the letter of your choice.

Kernel Boot Options: (see /etc/grub.conf or /etc/lilo.conf)

• nosysinfo :Disable NPL thread support. Used for RH 9.0 to fix incompatibility of Java version earlier than 1.4.1.
• root=LABEL=/ :Location of root of filesystem.

GRUB: GRUB allows one to boot one of many operating systems installed on the hard drives. GRUB can hide partitions from operating systems which is important when cohabitating with a Microsoft operating system. You can use a partition to install an operating system and hide the other partitions from it. (GNU: GRUB home page)

Grub was introduced with Red Hat 7.2 as the default boot loader. It's configuration file is /boot/grub/grub.conf. While lilo requires reconfiguration with new information loaded on the MBR for each new kernel, grub does not. Grub requires that the new kernel information be entered in the configuration file /boot/grub/grub.conf.

A Red Hat7.2 installation using lilo may be switched to grub using the command /sbin/grub-install. (i.e. /sbin/grub-install /dev/hda Specify the drive on which the boot loader will be installed on it's MBR.)

GRUB Menu:

1. Select kernel
2. Press 'e' to edit entry
3. Use arrow keys to navigate to kernel line. i.e. kernel /vmlinuz-2.4.7-1 ro root=/dev/hda2
4. Add argument 'single' to the end of the line. Then press return.
5. Press 'b' to boot.

The Red Hat 7.3 Installation/Upgrade offers three choices:

1. Update current: Update boot loader currently on the system.
2. Skip update
3. New boot loader configuration: Choose this if you wish to update from Lilo to Grub.

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