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basic introduction
User management diagram
illustrate
- Linux system is a multi-user and multi-task operating system. Any user who wants to use system resources must first apply for an account to the system administrator, and then enter the system as this account.
- Linux users need to belong to at least one group
Add user
basic grammar
useradd [options] username
actual case
Add a user xm.
Special Note
cd means change directory, switch directory
Details
- When the user is successfully created, a home directory with the same name as the user will be automatically created
- You can also specify a new user name for the directory through useradd -d, and specify the home directory for the newly created user
Assign or change a password for a user
basic grammar
passwd username
Applications
Specify a password for xm 
delete users
basic grammar
userdel username
Applications
- Delete user xm, but keep the home directory
- userdel username
- Delete user and user home directory
- userdel -r username
Precautions
When deleting a user, we generally do not delete the home directory
Query user information
basic grammar
id username
Applications
Please check root information
Details
When the user does not exist, return no such user
switch user
introduce
In operating Linux, if the current user has insufficient permissions, you can switch to a high-privileged user, such as root, through the su - command.
basic grammar
su – switch username
Applications
Create a user zf, specify a password, and switch to zf.
Details
- Switching from a user with high authority to a user with low authority does not require entering a password, and vice versa.
- When you need to return to the original user, use the exit command
View current user/login user
basic grammar
- whoami
- who am I
user group
introduce
Similar to roles, the system can manage multiple users with commonality in a unified manner.
Add group
groupadd group name
delete group
groupdel group name
Add groups directly when adding users
useradd -g user group username
Operation demonstration
Add a user zwj and assign him directly to wudang
Modify a user's group
usermod -g user group username
Case demonstration
User and group related files
/etc/passwd file
- User (user) configuration file, recording various information of the user
- The meaning of each line: Username: Password: User ID: Group ID: Commentary Description: Home Directory: Login Shell
/etc/shadow file
- password configuration file
- The meaning of each line: Login Name: Encrypted Password: Last Modified Time: Minimum Interval: Maximum Interval: Warning Time: Inactivity Time: Expiration Time: Flag
/etc/group file
- The configuration file of the group (group) records the information of the groups included in Linux
- The meaning of each line: group name: password: group identification number: list of users in the group
