RHCE-certified GRUB Study Notes

1. Concepts 1. startup manager is a program stored in the disk start sector, for example, the hard disk MBR (MasterBootRecord). After the system completes the startup test, if the system is started from MBR, the BIOS (BasicInput/OutputSystem) sends the control to MBR. The program stored in MBR will run. This program is called the start manager. Its task is to transfer the control to the operating system to complete the startup process.

1. Several Concepts

1.1 start Manager
The startup manager is a program stored in the Start sector of the disk. For example, the hard disk MBR (Master Boot Record). After the system completes the startup test, if the system starts from the MBR, the BIOS (Basic Input/Output System) sends the control to the MBR. The program stored in MBR will run. This program is called the start manager. Its task is to send control to the operating system and complete the startup process. There are many available start managers, including gnu grub (Grand uniied Boot Loader), Bootmanager, LILO (LInux LOader ), NTLDR (boot loader for Windows NT systems), etc.
1.2 What is GRUB?
Grub is a multi-startup manager. Grub is short for GRand uniied Bootloader. It can select which system to boot when multiple operating systems coexist. The following operating systems are supported:
Linux, FreeBSD, Solaris, NetBSD, BeOSi, OS/2, Windows95/98, Windows NT, Windows2000, WinXP. It can load the kernel of the operating system and initialize the operating system (such as Linux and FreeBSD), or give the boot permission to the operating system (such as Windows 98) to complete the boot.
1.3 features of GRUB
It is particularly suitable for the coexistence of linux and other operating systems.
Currently, lilo of most Linux releases has the same problem: the root partition (/boot partition) cannot be divided into more than 1024 cylinders, generally around GB, otherwise, lilo cannot be installed, or the system cannot be correctly booted after installation. Grub does not have this situation, as long as your big hard disk is in LBA mode during installation, grub can guide the operating system with a root partition of 8 GB.
Supports the boot screen grub supports displaying a boot screen while booting. For players, this allows them to create their own personalized boot screen; for PC manufacturers, this allows them to display some information about the computer and the manufacturer's logo at startup. Grub supports 640x480,800x600,102 4x768 boot screen in various modes, and can automatically detect and select the best mode, which is different from the boot screen of Windows x.
The two execution modes, grub, can not only perform routine boot through the configuration file, but also dynamically change the parameters during boot before selecting boot, as well as dynamically load various devices. For example, if you compile a new core in Linux, but you cannot determine whether it can work, You can dynamically change the grub parameter during boot and try to load the new core for use. The Grub command line has very powerful functions and supports history functions such as bash or doskey. You can use the up and down keys to find previous commands.
Select grub from the menu and use a menu to select different systems for guidance. You can also configure various parameters, such as the delay time and default Operating System.
After the partition size is changed, you do not need to reconfigure grub to directly read the core to the memory through the file system. Therefore, grub can guide the system as long as the path of the core of the operating system is not changed.
In addition, Grub has many very powerful functions. For example, OSS supports multiple external devices, dynamically loads the operating system kernel, and even mounts the operating system core through the network. Grub supports multiple file systems, multiple executable file formats, automatic decompression, multi-boot operating systems, and network startup.
1.4 MBR and first sector
You can simply understand that MBR is the first physical location of the entire hard disk, while the first sector is the second physical location of the hard disk.