17.0 The Boot Loader
This chapter describes how to configure GRUB, the boot loader used in
SUSE® Linux Enterprise. 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
Booting and Configuring a Linux System. A boot loader represents the interface between
machine (BIOS) and the operating system (SUSE Linux Enterprise). The configuration of
the boot loader directly impacts the start of the operating system.
The following terms appear frequently in this chapter and might need some
- Master Boot Record
The structure of the MBR is defined by an operating
system–independent convention. The first 446 bytes are reserved
for the program code. They typically hold part of a boot loader program
or an operating system selector.
The next 64 bytes provide space for a partition
table of up to four entries (see
Partition Types). The partition table contains information
about the partitioning of the hard disk and the file system types. The
operating system needs this table for handling the hard disk. With
conventional generic code in the MBR, exactly one partition must be marked
active. 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 some BIOSs, so is not considered for booting.
- Boot Sectors
Boot sectors are the first sectors of hard disk partitions with the
exception of 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 other
than XFS. 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 (AA55).