User and user group management, file permission management

1. Manage user accounts

1. Categories

Super user: The root user is the default super user account in the Linux operating system, and has the highest authority to the host. The super user is the only one in the system.
    Ordinary user: Created by the root user or other administrator users, the permissions they have will be limited. Generally, they only have full permissions in the user's own home directory.
    Program users: When installing the Linux operating system and some applications, some specific low-privilege user accounts will be added. These users are generally not allowed to log in to the system, and are only used to maintain the normal operation of the system or a program, such asbin, daemon, ftp, mail, etc.

2.uid logo

• The UID of the root user account has a fixed value of 0
• The default UID of the program user account is Centos5,6: 1~499, Centos7: 1~999
• The default UID for common users is Centos5, 6: 500~ 65535, Centos7: 1000~ 60000

Second, add user account useradd

useradd [options] username

-u specifies the user's UID

[[email protected] ~]# useradd -u 2000 helen //Add the helen user and specify the UID as 2000[[email protected] ~]# tail -1 /etc/passwd //View the information of helen in passwdhelen:x:2000:2000::/home/helen:/bin/bash

-s specifies the user's login shell (usually for program users)

[[email protected] ~]# useradd -s /sbin/nologin apache //Create a user and specify the login shell as /sbin/nologin, the user cannot log in to the system[[email protected] ~]# tail -1 /etc/passwdapache:x:2008:2008::/home/apache:/sbin/nologin

Three, set/change the user password passwd

passwd [username]

Set or modify user password

[[email protected] ~]# passwd nancy //Set or modify the password of the nancy userChange the password for user nancy.new password:Re-enter new password:passwd: All authentication tokens have been successfully updated.[[email protected] ~]# echo "linux666" | passwd --stdin nancy //Easy to set user passwordChange the password for user nancy.passwd: All authentication tokens have been successfully updated.

Fourth, modify the attribute usermod of the user account

usermod [options]... username

[[email protected] ~]# usermod -l sasha helen //Change the username of helen to sasha[[email protected] ~]# usermod -L sasha //Lock user sasha[[email protected] ~]# passwd -S sasha //View sasha status, it has been lockedsasha LK 2022-02-21 0 99999 7 -1 (Password is locked.)[[email protected] ~]# usermod -U sasha //Unlock user sasha[[email protected] ~]# passwd -S sasha //View sasha status, normal status

Five, set the attribution of files and directories chown

chown owner file or directory //modify owner
chown:group file or directory //modify group
chown owner:group file or directory //modify owner and group

-R: recursively modify the ownership of all files and subdirectories in the specified directory

Six, file and directory permissions management chmod

The read, write, and execute permissions of the file can be represented by the characters r, w, x, or as the octal numbers 4, 2, and 1, respectively