Linux system startup process

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