A thorough understanding of the Linux startup process is a key point of knowledge, and only when this is known will it be very cool and quick to debug in the event of a system-level error at Linux.
The first phase of the Linux startup process
- BIOS is not the operating system's scope of responsibility
- BIOS is the function of hardware, belonging to firmware
- The BIOS is stored in ROM, and the data can be saved without the need for strong power.
- Changes to the BIOS are saved in a specific RAM in order to ensure that the actual change is saved after the power outage, and the battery is added to the BIOS to resolve
- The BIOS can select the boot sequence (hard disk, CD, network, etc.)
- If you select the BIOS to boot from the hard disk, the hard disk must be MBR partition, the corresponding supported hard disk maximum is 2TB
- Replaces the BIOS with UEFI (Unified extensible Firmware Interface), usually with hard disk partition type GPT, supports maximum hard disk 8ZB
- Once the BIOS locates the boot program bootloader in the MBR partition of the hard disk, it transfers the follow-up work to bootloader
Phase II
- Bootloader loading the kernel into memory
- Whenever the MBR of a device is read, if the bootloader in the MBR is corrupted and fails to start properly, the operating system will not read the MBR of the second device, which is due to bootloader corruption. We need to change the boot order of the BIOS from the CD boot to repair the bootloader in the hard drive
- Once the kernel loaded, bootloader quit work, the follow-up work to kernel.
Bootloader Detailed:
Bootloader is a program that does not belong to any operating system, but is provided by the operating system when it is installed. Common with Microsoft's Ntloader. There are two common types of bootloader for Linux:
- LILO: Hard drives larger than 8G are not supported and are commonly used in embedded systems
- Grub:grand Unified Bootloader, currently has two mainstream versions grub-0.97 and grub2-2.02, is the process of creating Bootloader during the installation of Linux
Phase III
- Kernel kernel to perform/sbin/init, you must be able to access the root file system first, because under Linux, the FileSystem starts with the root/directory, which is the root filesystem rootfs
- Linux is a single-core architecture
- The kernel itself is as small as possible, because the kernel is resident memory, and the kernel needs to support as many types of hardware as possible, through a modular design. Ko for dynamic loading and unloading of kernel modules.
Introduction to the Linux startup process and recovery methods for each startup phase failure
