16. system startup process

centos6 System startup process

1. Boot up and load BIOS, Perform power on hardware self-test （ Check the hardware for problems ）
2. Load disk ,0 head ,0 Magnetic track ,1 On sector MBR Guidance record , Then boot the system
3. Get into GRUB menu , Select load kernel information （ Choose a different kernel ）
4. Load system kernel information （kernel）
5. Start the first system process init,（ Make other services start in sequence in a serial way ）
6. Load the system runlevel file ,/etc/inittab
7. Load the system initialization script file ,/etc/rc.d/rc.sysinit Script
8. Load the system service script storage directory , Enable services of different operation levels to be started chkconfig
9. start-up mingetty process , Load and display the system login interface

centos7 System startup process

1. Boot up and load BIOS, Perform power on hardware self-test
2. Load disk ,0 head ,0 Magnetic track ,1 On sector MBR Guidance record , Then boot the system
3. Get into GRUB menu , Select load kernel information
4. Load system kernel information
5. Start the first process of the system ,systemd( In a parallel way, other services can be started at the same time )
6. according to target Mode select system startup level /etc/systemd/system/default.target
7. Load system initialization target Script files /usr/lib/systemd/system/sysinit.target
8. Load response system unit Unit file , Realize the automatic startup of the service , Define the startup service /etc/systemd/system( According to the operation level of the system , Start different services at startup )
9. start-up mingetty process , Load and display the system login interface