Shulou(Shulou.com)06/03 Report--

First of all, let's look at the following picture:

1. Power-on self-test

Firmware: combination of hardware and software. Power-on self-test is that when we press the power supply, we will detect hardware such as cpu, memory, network card and other information. (check whether the hardware is available at the hardware level)

2. Bootstrap program

After testing, jump to mbr (master boot record) to read a very important data bootloader (all subsequent work is done by bootloader) and partition table, magic number.

3. Bootloader loads the kernel

Kernel concept: (linux is a pile of source code. When you boot, you will see booting the kernel to check whether the hardware is available at the software level.)

There are two main functions: drive hardware (the so-called driver is that the system recognizes the hardware, let the operating system recognize the hardware, and identify whether the hardware is available from the software), and the task is completed after starting the init process.

4. Start the init process (the first process started by linux)

Tasks of the init process:

Explanation:

The pid of the init process is 1, and its PPID is 0pm Ppid, which is the parent process ID, and its parent process is the kernel task scheduler.

Linux is a real-time system that allocates processing time by time. If you don't finish processing this time and then process it the next time you continue to allocate time, you need a CPU time scheduler, that is, a kernel scheduler with a PID of 0.

A process derived from a process in linux becomes a child process. If the parent process of a process dies, its child process cannot exist. In linux, the parent process dies, the child process survives, and the orphan process is not allowed in linux. When linux scans for an orphan process, it automatically sets the parent of the orphan process to the init process (a process with a PID of 1).

If the child process dies, the parent process should switch the connection between the child process and the child process. This child process becomes a zombie process, J process, and this kind of process is not allowed to exist.

5. Read / etc/inittab file

Summary:

(1) fireware (firmware) post to check whether the hardware device is normal. If so, read the bootloader in MBR (Master Boot Record), the first location where the data is stored on the hard disk.

(2) the most important thing in BootLoader is to store a bootstrap program (GRUB).

(3) GRUB loads kernel (kernel) to drive hardware and start init process

(4) init process read / etc/inittab

First execute the script: / etc/rc.d/rc.sysinit (this script will be executed regardless of any run level), then find the default run level according to initdefault and execute the script under / etc/rc.d/rcN.d. The script that begins with S is the script that starts the service, and the script that starts with K is the script that shuts down the service.

(5) finally, a terminal will be set up and wait for the user to log in. Displays user, name.

These are the details of the linux system boot process, please pay attention to other related articles!

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.