(5) Analysis of Linux boot process and linux boot process

(5) Analysis of Linux boot process and linux boot process

　　Directory

• Linux boot process
• Linux running level
• Linux Startup Service Management
• GRUB configuration and application
• Start Fault Analysis and Resolution

 

Linux boot process

 

The Linux boot process is as follows:

　　

 

Firmware is a program written into EROM or EEPROM (programmable read-only memory). Generally, it can be called a Firmware only when it serves as the most basic and underlying software for a digital product, for example, the Basic Input/output System BIOS (Basic Input/output System) on the computer motherboard is actually called by more professionals.

Generally, the programs stored in these hardware cannot be directly read or modified by users. In the past, there was generally no need to upgrade the firmware, even if a major Bug is found in the firmware, a professional must replace the original machine with a program chip. With the continuous development of technology, it has become an urgent requirement for users to modify firmware to adapt to the constantly updated hardware environment. Therefore, the Programmable Erasable read-only memory EPROM (Erasable Programmable ROM) can be repeatedly written ), the emergence of EEPROM and flash, these chips can be repeatedly written, so that the firmware can be modified and upgraded.

When the computer is powered on, the system will execute a self-check routine. This is the most important feature of the firmware BIOS. It is usually called POST-Power On Self-Test)

Common firmware settings include security settings, list of bootable media, sequence of searching for bootable media, power management, and display of startup details.

 

View System Time (Software Clock): date view hardware clock: hwclock

　　

　　

For example, if the system time and hardware clock are basically the same and accurate, if either of them is inaccurate, You need to synchronize them by referring to the other clock, run the hwclock -- help Command to view the help information of common hwclock options. You can see that the -- hctosys option sets the system time based on the hardware clock, and the -- systohc option sets the hardware clock based on the current system time.

　　

 

If the system time and hardware clock are not accurate, we need to reset it. For the system time, we use man date to see its help documentation, the system time format is date, month, day, hour, minute, year, and year. seconds. For example, if you set the current system time to, January 1, April 15, 2015, the command is date 041514252015.30.

　　

 

Similarly, we can use man hwclock to view the help document of hwclock. The command for setting the current hardware clock to April 15, 2015 14:25:30 is hwclock -- set -- date = "4/15/2015 ", of course, you can also set the hardware clock according to the current system time.