CENTOS6 system Start-up process

Analyze the entire process of booting to the login interface:

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Post power-on self test : Mainly check the hardware is normal, according to Cmos/bios code to look for boot media (mainly hard disk). Found by boot squence bootloader

read MBR: MBR exists on the hard disk 0 track 0 cylinder on the first sector, the size is 512 bytes, where the first 446 is bootloader,64 bytes is the disk partition table, the latter two are used to verify the

Bootloader (boot loader): Provides a menu that allows the user to select a system to boot or a different kernel version, to load the selected kernel into a specific space in memory, unzip it, and then transfer the control of the system to the kernel. (and bootloader inside the program is grub, its role is to start the kernel, grub is composed of two parts, Stage1 and Stage2,stage1 is inside the MBR, in order to boot stage2. Stage2 are stored on partitioned file systems, and partitions are not recognized until the system is started. You need to stage1.5 this middle layer to assist Stage1 to find Stage2, when stage2 boot, will parse/boot/grub/grub.conf to load the kernel)

load Kernel : According to the flowchart, the function of the kernel is to complete its own initialization (detect all the hardware devices that can be identified, load the hardware driver (possibly with the help of RAMDisk load driver), mount the root filesystem in read-only mode, and run the first program of user space:/sbin/ Init, giving control of the system to the/sbin/init process)

System Initialization : When the/sbin/init process takes over the kernel, reads the/etc/inittab file (CENTOS6 does not place the execution steps in the Inittab file like CETONS5, but instead places the configuration file in a shard to/etc/ init/*.conf in each file)

To execute the/etc/rc.d/rc.sysinit script to initialize the system first, the initialization mainly consists of:

Set host name

Set Welcome info

Activating Udev and SELinux

mount the file system inside the/etc/fstab

Set the network clock

Re-mount the root file system in read-write mode

Activating swap Devices

Setting kernel parameters According to the/etc/systmctl.conf file

Activating LVM and soft raid devices

Operations such as cleanup operations

then according to the default operating level of the system (Id:3:initdefault:) to execute/ETC/RC.D/RC this script, according to the default level, find the/etc/rc.d/rc#.d/directory of the link file (k means stop,s means start) To execute scripts that/etc/init.d/each service

After the above process is executed, the/etc/rc.d/rc.local script is executed, and if there is an X script that needs to be started with the system, it can be placed within the secondary script.

After all the system startup tasks have been completed, Linux will start the terminal or X-window to wait for the user to log in. Tty1,tty2,tty3...tty6 This means that in the run Level 1,2,3...6 terminal, will execute will execute/sbin/mingetty, the landing interface, the system started to complete.

CENTOS6 system Start-up process