User Decentralization Modify the root user password

The user is the identity of the system user, and the user exists as the data identity. The user is stored in the system as several characters plus several system configuration files

System configuration files involved in user information (1) /etc/passwd ###User information

user: password: uid: gid: description: home directory: the shell used by the user

As shown below, enter cat/etc/passwd in the shell window to find out the user's information

(2) View user authentication information 
User: Password: Last password modification Time: Minimum validity period: Maximum validity period: Warning period: Inactive period: Account expiration date 

Enter cat /etc/shadow to find out user authentication information. 

(3) View group information 
Group name: group password: group id: additional group members 

Enter cat /etc/group to find out group information. 

(4) /etc/gshadow ### group authentication information 

Enter cat /etc/gshadow to find out the group authentication information.

(5) /home/username ### User home directory 
(6) /etc/skel/.* ### User skeleton file 

Type cat /etc/skel/.* to find out the user skeleton file. 

Note that the following must be emphasized. *

User management

1. User establishment

useradd parameter username

Create a user "hello", as shown below

parameter

-u ##Specify user uid

-g ###Specify the user's initial group information, this group must exist

-G ### Specify additional groups

Appropriate use of surveillance

watch  -n 2 'tail -n 1 /etc/passwd /etc/group;ls -l 

Through the above experiments, we can clearly see the effect of each parameter

Use userdel -r username to delete users and configurations

As shown in the figure below, id -a westos can display all the information of the user;

Add parameters - u, -g, -G to query the user's uid, initial group id, and all group ids respectively

usermod parameter user -l ##change username -u ## change uid -g ## change gid -G ##change additional group

- aG ##Add additional group - c ##Change description - d ##Change home directory designation - md ##Change home directory designation and home directory name

3. User decentralization 
(1) In the system, super users can delegate operations that ordinary users cannot perform to ordinary users 

Decentralized power configuration file: /etc/sudoers

Use visudo to enter /etc/sudoers to edit

在100,101行添加##Allow hello to run useradd and userdel on localhost

hello localhost=(root)  NOPASSWD:/sbin/useradd, /sbin/userdel

Execute the decentralization command 
sudo command## If you execute sudo for the first time, you need to enter the current user password 
in /etc/sudoers If the settings are as follows:

test  desktop0.example.com=(root)  NOPASSWD： /usr/sbin/useradd

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Indicates that the user does not need their own password when calling the sudo command

When we finish editing and save the file, we can use the delegated power, as shown in the following figure

User authentication information

chage   参数  用户
    -d  ##用户密码组后一次修改的时间，如果设定成0，用户登陆系统后必须修改自己的密码 
    -m  ##最短有效期
    -M  ##最长有效期
    -W  ##警告期
    -I  ##用户非活跃天数
    -E  ##帐号到期日格式 -E "YYYY-MM-DD"

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The chage command and parameters are used as shown in the following figure

When using the -m parameter to change the shortest validity period to 1 (indicating that the password needs to be changed after one day), if you change the password immediately, you will get the following prompt, indicating that you need to wait for a period of time to change the password

Forgot root password  , the
operation procedure is as follows: 
1. Restart the system 

2. During the system startup phase, press the up and down keys to stop the system from booting 

3. Select Boot Boot Title, press "E" to edit

Press E to enter the interface as shown below

 Find the linux16 boot entry line, delete the ro option from the end of this line, and change ro to rw, then add the rd.break option

The modified result is shown in the following figure

5.ctrl+x to start the system boot entry after setting 
6. After entering the system, execute chroot /sysroot to switch to the real system environment 
7.passwd root Change the superuser password 
8. Create a file /.autorelabel to let the system scan all files ( touch /.autorelabel) 
9.exit twice to automatically restart the system 

The operation of steps 6-9 is shown in the figure below.

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