1. Read the MBR information and start boot Manager
Windows uses NTLDR as the boot Manager, and if you have multiple versions of Windows installed on your system, you will need to select the system you want to enter in NTLDR.
Linux typically uses a powerful, configurable grub as the boot manager, and we'll show you how it is used in the Launch Management section.
2, load the system kernel, start the init process
The init process is the root process of Linux, and all system processes are its child processes.
3, the Init process reads the information in the "/etc/inittab" file and goes to the preset run level, running the script under the corresponding folder in the run level in order. Scripts are usually started with the "start" argument and point to a program in a system.
Typically, the startup script under the "/etc/rcs.d/" directory is executed first, followed by the "/etc/rcn.d/" directory. For example, if you set a run level of 3, then its corresponding startup directory is "/etc/rc3.d/".
4, according to the "/etc/rcs.d/" folder in the corresponding script to start the Xwindow server "Xorg"
Xwindow is a graphical user interface system under Linux.
5, start the login manager, waiting for users to log in
The Ubuntu system defaults to using GDM as the login manager, and you can log in to the system after you enter your username and password in the Login manager interface. (You can find a link in the "/etc/rc3.d/" folder named "S13GDM")
If you want Ubuntu to boot to command prompt each time, you can enter the following instructions:
$echo "false" | sudo tee/etc/x11/default-display-manager
When the next boot, will be in the command mode to start, if you want to change back to start X window, you can enter:
$echo "/USR/BIN/GDM" | sudo tee/etc/x11/default-display-manager