One: Post power-on self-test
II: BIOS--->boot Sequence
Follow the hardware boot setup in the BIOS to find the boot device sequentially.
The first device that has a boot program is the device that is used for this boot.
Three: MBR--->bootloader
MBR composition:
446:bootloader------CentOS Grub
64: Partition Table information
2: Whether to enable
Four: Kernel loaded into memory
Initialize (self-extracting):
Detect all hardware devices that can be identified;
Load hardware drivers (may be loaded with ramdisk);
The system has been installed to mount the root file system;
Run user space The first application:/sbin/init
Init program Type:
Sysv:init,centos5
Configuration file:/etc/inittab
Upstart:init,centos6
Configuration files:/etc/inittab,/etc/init/*.conf
Systemd:systemd,centos 7
Configuration files:/usr/lib/systemd/system,
/etc/systemd/system
/sbin/init Program:
Operating level: Set for application purposes such as system operation or maintenance
0,6,: Shutdown, restart
1, 2,: Maintenance Mode (single-user mode, multi-user mode)
3,5,: Default level (3 text interface, 5 is graphical interface)
Switching level: Init NUM
View level: RunLevel
Who-r
Configuration file:/etc/inittab
Chkconfig command--View the startup or shutdown settings scenario for all levels of the service.
Chkconfig [--list] [name]
Added: Chkconfig--add name
Delete: Chkconfig--del name
To modify the specified link type:
Chkconfig [--level levels] name <on|off|reset>
V:/etc/rc.d/rc.sysinit: System Initialization script:
(1) Set the host name;
(2) Set welcome information;
(3) Activate Udev and SELinux;
(4) Mount the file system defined in the/etc/fstab file;
(5) Detecting the root file system and re-mounting the root file system in read-write mode;
(6) Set the system clock;
(7) Activate swap device;
(8) Set kernel parameters according to/etc/sysctl.conf file;
(9) Activating LVM and software RAID devices;
(10) Loading the drivers for additional devices;
(11) Cleaning operation;
Summarize:
post power On self-check-out BIOS (Boot Sequence)--MBR (bootloader)--Kernel/sbin/init ---> (/etc/inittab,/etc/init/*.conf)--Set default run Level---> Run System initialization script -- Close or start the corresponding service----> set the login terminal
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Linux system startup process