Linux User Group Management

1. Linux user account management

    In the linux system, whether it is from the local machine or remote login system, each system must have an account, and have different permissions to use different system resources

    In Linux, you can specify different permissions for different files or directories for each user

    

 
2. Linux user group management

    In practical applications, you can set permissions for groups in advance, and then add different users to the corresponding groups, so you don’t need to set permissions for each user in turn

    

 

3. User-related configuration files

   User information file: /etc/passwd
   Password file: /etc/shadow
   User group file: /etc/group
   User group password file: /etc/gshadow
    1./etc/passwd

      Each user in the Linux system has a corresponding record line in the /etc/passwd file, which records some basic attributes of each user

     

     A row of records in /etc/passwd corresponds to a user, and each row of records is separated into 7 fields by a colon (:). The format and specific meaning are as follows:

           Username: Password: User Identification Number: Group Identification Number: Annotative Description: Home Directory: Login Shell

           User identification number (UID): In fact, the user's authority is determined by the UID number. There are three types of Linux users:

                                             Super user: (root UID=0)
                                             Ordinary user: (UID 500~60000)
                                             Pseudo user: (UID 1~499)
                                           So, we can modify the user’s UID number to modify the user’s type
            Pseudo users: These users also have a record in the /etc/passwd file, but cannot log in because their login shell is empty. Their existence is mainly to facilitate system management and meet the requirements of corresponding system processes for file owners.
    2./etc/shadow

      The record line in /etc/shadow corresponds to the one in /etc/passwd, which is automatically generated by the pwconv command based on the data in /etc/passwd

          

     Its file format is similar to /etc/passwd, consisting of several fields, separated by ":". These fields are

   Login name: Encrypted password: Last modification time: Minimum time interval: Maximum time interval: Warning time: Inactivity time: Expiration time: Sign

   The pwconv: command is used to turn on the user's projection password. The user and group passwords in the Linux system are stored in files named passwd and group respectively, and these two files are located in the /etc directory. Because the system needs to operate, anyone can read them, causing security breaches.
          Projection password changes the password in the file to the shadow and gshadow files in the /etc directory, which can only be read by the system administrator, and the original password is replaced with the "x" character. However, this action is usually done automatically by linux
   pwunconv: command is used to close the user's projection password.
   3./etc/group

      Each user belongs to a certain user group; there can be multiple users in a group, and a user can also belong to different groups.

      When a user is a member of multiple groups at the same time, the main group to which the user belongs is recorded in the /etc/passwd file, which is the default group to which the user belongs when logging in, and other groups are called additional groups. When a user wants to access files belonging to an additional group, he must first use the newgrp command to make himself a member of the group he wants to access.