Shulou(Shulou.com)06/02 Report--

1. BIOS detailed explanation

BIOS (Basic Input/Output System), the basic input and output system, the system is stored on the ROM chip of the motherboard. When the computer is powered on, it will first read the system, and then there will be a power-on self-test process, this process is actually to check CPU and memory, the most basic components of the computer (controller, calculator and memory), but also check other hardware, if there is no exception, begin to load BIOS programs into memory. Let's not talk about the detailed BIOS function here. One of the main functions of BIOS is to store the boot order of the disk. BIOS will look up the MBR information of the first disk head according to the startup order, and load and execute the Bootloader program in MBR. If the first disk does not have MBR, it will continue to find the second disk (PS: the boot sequence can be set in the BIOS interface). Once the BootLoader program is detected and loaded into memory BIOS transfers control to the BootLoader program.

1. System startup process

Step 1: power on the computer

Step 2: BIOS (read-only storage ROM on motherboard, basic input or output system)

Function, hardware detection, activation of hardware

Step 3: grub system boot (grub boot is divided into two stages)

1) Phase 1 grub disk boot phase

Mbr (Master Boot record) the 0 track, one sector, 446 bytes recorded by the master boot on the hard disk.

(MBR (Master Boot Record), master boot record, MBR is stored in the head of the disk, the size is 512bytes, wherein, 446bytes is used to store BootLoader programs, 64bytes is used to store partition table information, and finally 2bytes is used to check the validity of MBR.

)

1./dev/zero of=/dev/vda bs=446 count=1 can empty mbr

1) chroot / mnt/sysimage switch to real / environment

And execute grub2-install / dev/vda

2) Phase 2 grub file boot phase

Find / boot partition

Read / boot/grub2/grub.cfg / etc/grub.cfg

File missing, grub2-mkconfig > / boot/grub2/grub.cfg

Grub2-mkconfig > / etc/grub.cfg

Step 4: kernel boot phase:

Boot kernel, read-only mount / device

two。 Detection of hardware equipment

3. Initialize the device driver

4. Enter the system initialization phase and mount it

Kernel loss can be solved by re-installing the kernel installation package.

Method 1: rpm-ivh kernel-xxxxx.rpm-force

Method 2:

1. In virt-manager, put the optical drive IDE CDROM1 in the first place of the boot item, and boot the host to enter rescue mode

2.chroot / mnt/sysiamge changes the system mount to the root directory

3.mount / dev/sr0 / westos mounts CD files

4.cd / westos/ switch to CD mount point

5.ls View the files on the CD

6.cd Packages/ changes to the installation package directory (remember, no ls, there are more than 4000 packages)

7.cp kernel-3.10.-123.e17.x86_64.rpm / mnt/

Copy this package to / mnt/ because it cannot be unpacked in the CD directory

8.cd / mnt/ switch to / mnt/

9.ls View the copied package under / mnt/

10.rpm2cpio kernel-3.10.0-123.e17.x86_64.rpm | cpio-id

Unpack

11.ls view the files in the package

12.pwd View current path

13.cd boot/ changes to the boot/ directory in the package

Kernel file exists in 14.ls-l package

15.cp vmlinuz-3.10.0-123.e17.x86_64 / boot/

Copy the kernel file to the / boot/ directory of the system

16.exit exits the root directory changed by chroot

Exit shell window

Step 5: system initialization phase

1. Load initrd image during system initialization

How to solve the problem of initrd image loss?

Initramfs-uname-r.img missing use:

Mkinitrd initramfs-uname-r.img uname-r

* method 1: * * 1. When the system does not restart, the current version 1) mkinitrd / boot/initramfs- `uname − r`.img `uname-r` generates the system initialization image initramfs is / boot/grub2/grub.cfg file has been written, cannot change 2) mkinitrd / boot/initramfs-$ (uname-r). Img $(uname-r) # # generate system initialization image * * method 2: * *

1) enter into rescue mode

1..chroot / mnt/sysiamge uses superuser

2.mkinitrd / boot/initramfs-uname − r.img uname-r generate system initialization image

The restart will be slower.

Reason: rescan selinux

Solution: change enforcing to disabled in / etc/sysconfig/selinux

Step 6: start the initialization process systemd

1. Start selinux

two。 Load kernel parameters

3. Initialize system clock, keyboard, host name

4. Reread the mount / device

5. Activate raid,lvm

6. Activate quota

Start all services in multi-user.target.wants (which services are enabled depending on the level at which the system starts)

7. Open the virtual console

8. Launch Drawin

How do I modify the system startup level?

System boot level

(init 0) runlever0.target-> poweroff.target

Runlever1.target-> rescue.target

Runlever2.target-> multi-user.target

(init 3) runlever3.target-> multi-user.target

Runlever4.target-> multi-user.target

(init 5) runlever5.target-> graphical.target

(init 6) runlever6.target-> reboot.target

Method 1: systemctl set-default + startup level

Method 2: / etc/systemd/system/default.target

Step 7: login with username and password

How can I forget my password?

1. Start up and press the upper and lower keys to stop reading seconds

two。 Press E to enter edit mode

3. Select kernel startup line

Change Linux16 / vmlinuz-xxxxx ro xxxx to:

Linux16 / vmlinuz-xxxxx rw rd.break # # terminates the execution of the system initialization program after kernel startup is completed

4. Start the system ctrl+x

Chroot / sysroot

Echo westos | passwd-- stdin root

Touch / .autorelabel # # reinitialize selinux. No action is required when selinux is not enabled

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