Analysis of startup process of Linux system

Linux Boot Sequence

Motherboard BIOS power-on self-test hardware

-Read hard drive boot sector (MBR)

-Boot Boot program (GRUB)

-Select System

-Load the system kernel (kernel shell)

-Start the system to read the corresponding default settings (environment variables, runlevel)

--Start the appropriate services and processes

--Landing System interface

Boot program configuration file

/etc/grub2.cfg

To view all boot levels

#cd--/usr/lib/systemd/system ls

1. (1) View the default boot level for the current boot

#systemctl Get-default

To modify the default startup level

Example: Level 3--"Level 5

Ln-sf/usr/lib/systemd/system/graphical.target/etc/systemd/system/default.target

Example: Level 5--"Level 3

Systemctl Set-default Multi-user.target (level to modify)

[note] RunLevel can only be modified by means of a soft connection

Simulated accident

Level 0 that will be modified to start the system will not start

Repair:

Reboot into Grub Boot interface

--up and down arrows end countdown

--Press the E key to enter the startup parameter settings

--Find Linux16 at the end of the line UTF-8 add systemd.unit = Rescue.target (Specify mode to enter the system)

-->ctrl x (startup parameter setting)

Crack root Password

Reboot into Grub Boot interface

--up and down arrows end countdown

--Press the E key to enter the startup parameter settings

--Method ①: Find Linux16 to modify ro to RW init =/systemctl/bin/sh (enter root into the system default shell) to avoid hard drive loading

--method ②xd:utf-8 after adding keyword Rd.break

-->ctrl x

:/#mount View mount table, check whether the mount permission of the root partition is RW, if RO, need to mount, load permissions

:/#mount-O remount,rw/sysroot re-mount, load permissions

:/#chroot/sysroot/bin/bash Toggle Normal Startup Bash

:/#unset LANG Clear language environment variables

:/#passwd Change Password

:/#getenforce View selinux status

If SELinux is not closed, you need to allow SELinux to accept the new password

:/#touch/.autorelabel Create an associated tag file under/

:/#exit back to SH

:/#reboot Restart to verify the new password

Analysis of startup process of Linux system