You may not realize it unless you are dual booting multiple operating systems, but after your BIOS starts firing up the fan, the microprocessor chip, and the power supply, a boot manager, or bootloader, takes over the process until the kernel starts up.
Linux supports a variety of open-source and proprietary boot managers, but you can install only two with YaST: the Grand Unified Bootloader (GRUB) and the Linux Loader (LILO). GRUB has been the default bootloader for SUSE Linux since v8.2, but LILO still runs quite a few systems, and you may want to use it instead.
LILO succeeded load in as the primary Linux bootloader and seems to be in the long process of being superseded by GRUB. LILO carries out its single task, booting to a file system, well. It is not quite as flexible nor as configurable as GRUB. Nonetheless, it is still the default bootloader for systems in which the Root partition is installed on CPU-dependent RAID controllers (such as many Promise or Highpoint controllers), Software RAID, or Logical Volume (LVM) managed disk.
The chief difference between the two bootloaders is in how they find and load file systems. LILO looks for a file system based on where the partition table says it is. GRUB can read and identify several file systems (ext2, ext3, ReiserFS, JFS, XFS, Minix, and DOS).
In YaST, the Boot Loader Configuration module is on the System page. You can set LILO as the default if you want and set many other options in this screen. If you prefer, you can edit the file directly by clicking Edit Configuration Files.
By default, GRUB displays a menu, allowing you to boot SUSE Linux from the hard drive, from a floppy drive, or into fail-safe mode. Fail-safe mode loads a kernel version with a set of parameters that makes it possible to boot with some hardware problems. If there's another operating system on your computer, GRUB will list this on your boot menu as well. After 8 seconds, GRUB will boot the first item on the menu; that is, SUSE Linux. At the bottom of the GRUB menu, you can specify options for the kernel, if you are so inclined.
You can see how each process builds on the previous one, allowing different operating systems to work on the same hardware. The GRUB menu you see is controlled by the GRUB configuration file, which is located at /boot/grub/menu.lst.
The first portion of menu.lst defines options for the display of the GRUB menu, such as the color scheme of the menu, the default menu option, and the number of seconds (timeout) before GRUB runs the default menu option.
Following the display options are a list of items that will be displayed in the GRUB menu. Each menu item begins with "title." This particular GRUB menu will display three items:
• SUSE LINUX 10.0
• Floppy
• Failsafe—SUSE LINUX 10.0
The remaining lines tell GRUB where to find the operating system files needed to run Linux. These include the following:
• root: This command sets the current root device to the specified device.
• kernel: This command loads the primary boot image from the boot image file.
• initrd: This command loads an initial ramdisk for the boot image.
To configure how GRUB boots your system, you can either manually edit menu.lst with a text editor, or you can use the YaST System, Boot Loader module. In addition to manually editing the menu.lst file and using YaST, you can also use the GRUB shell to configure how your system boots. Simply enter grub at the shell prompt. To learn how to manipulate GRUB from the shell, see the grub man page.
Source of Information : SUSE Linux 10 Unleashed
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