Table of Contents
This chapter describes how to configure GRUB, the boot loader used in SUSE LINUX. A special YaST module is available for performing all settings. If you are not familiar with the subject of booting in Linux, read the following sections to acquire some background information. This chapter also describes some of the problems frequently encountered when booting with GRUB and their solutions.
This chapter focuses on boot management and the configuration of the boot loader GRUB. The boot procedure as a whole is outlined in Chapter 7, Booting and Configuring a Linux System. A boot loader represents the interface between machine (BIOS) and the operating system (SUSE LINUX). The configuration of the boot loader determines the operating system to start and its options.
The following terms appear frequently in this chapter and might need some explanation:
The structure of the MBR is defined by an operating system–independent convention. The first 446 bytes are reserved for program code. They typically hold the boot loader program, in this case, GRUB. The next 64 bytes provide space for a partition table of up to four entries (see Section 18.104.22.168, “Partition Types”). The partition table contains information about the partitioning of the hard disk and the file system type. The operating system needs this table for handling the hard disk. The last two bytes of the MBR must contain a static “magic number” (AA55). An MBR containing a different value is regarded as invalid by the BIOS and all PC operating systems.
Boot sectors are the first sectors of hard disk partitions except for the
extended partition, which merely serves as a “container” for
other partitions. These boot sectors have 512 bytes of space for code
used to boot an operating system installed in the respective partition.
This applies to boot sectors of formatted DOS, Windows, and OS/2
partitions, which also contain some important basic data of the file
system. In contrast, the boot sectors of Linux partitions are initally
empty after setting up a file system. Therefore, a Linux partition is
not bootable by itself, even if it contains a kernel
and a valid root file system. A boot sector with valid code for booting
the system has the same magic number as the MBR in its last two bytes
In the easiest case—if only one operating system is installed on a computer—the boot management takes place as described above. If several operating systems are installed on a computer, the following options are available:
One of the operating systems is booted from the hard disk. The other operating systems are booted by means of a boot manager installed on an external medium (floppy disk, CD, USB storage medium). Because GRUB is able to boot all other operating systems, no external boot loader needs to be used.
A boot manager enables concurrent installation and alternate use of several systems on one computer. The users can select the system to boot during the boot process. To change to another system, the computer must be rebooted. This is only possible if the selected boot manager is compatible with the installed operating systems. GRUB, the boot manager used in SUSE LINUX, is able to boot all common operating systems. By default, SUSE LINUX installs the selected boot manager in the MBR.