Before we move into these 4 process let see how to initiate Linux boot process. So, this can be achieve in 2 ways. First method is to start Linux device which is in stopped or halted mode. Second method is to reset or reboot the running system.
- BIOS POST: The word POST stands for power on self test . In this process BIOS runs a POST test to ensure that all the hardware devices connected to the system are functioning correctly. If POST fails the system will not be operable and the system will not proceed to second stage.
- Boot Loader: After a successful POST test the BIOS loads and executes the boot code from boot device located in the first sector of the hard-disk called boot device . In Linux this is located in /BOOT file system. The boot loader provides the user with boot screen often with multiple options to boot into such as windows o.s. or ubuntu etc. in case of dual boot system. Once the selection is made at the boot screen the kernel is loaded into the memory and then hands over the control to kernel.
- Kernel Initialisation: After the selected kernel is loaded into the memory the kernel is decompressed. As the kernel is in compressed form to conserve some space. The kernel is then loaded into the memory and starts executing. During this space kernel carries out task such as initialising task and memory management tasks along with other things. Once it is completely operational it looks for init process to run, which sets up user space and processes needed for user environment.
- Service Initialization: The INIT function then calls systemd daemon. The systemd is then responsible for bring the LINUX host to usable state.Systemd is responsible for mounting file system, starting and managing system services.
To check the init system used run ls -l /sbin/init.
Director Of Advance Training
4 个月Learning the boot process is essential. If you want to take CompTia Linux)+. Learn the Boot Process.