How to view user groups in Linux

Linux can use the following command to view user groups:

groups View the group members of the currently logged in user
groups gliethttp View gliethttp The group the user belongs to, and the members of the group
whoami Check the current login user name

Concepts of user (user) and user group (group):
1. User (user ) concept;
Through the previous understanding of Linux multi-users, we understand that Linux is a multi-user operating system in the true sense, so we can create several users (users) in the Linux system. For example, our colleague wants to use my computer, but I don’t want him to log in with my username, because there are materials and information (that is, private content) under my username that I don’t want others to see. Then I can give him He created a new username and asked him to use the username I created. This is in line with the operating rules from the perspective of computer security;

Of course, the conceptual understanding of user (user) is not only At this point, there are some users in the Linux system that are used to complete specific tasks, such as nobody and ftp. The web program we access LinuxSir.Org is the nobody user; when we access ftp anonymously, we will use the user ftp or nobody; If you want to know some accounts of the Linux system, please check /etc/passwd;

2. The concept of user group (group);
User group (group) is users with the same characteristics ( user); for example, sometimes we want multiple users to have the same permissions, such as viewing, modifying a certain file, or executing a certain command. In this case, we need user groups. We define all users to the same user group. We By modifying the permissions of the file or directory, the user group has certain operating permissions, so that the users under the user group have the same permissions for the file or directory. This is achieved by defining the group and modifying the permissions of the file;

For example: In order to allow some users to have permission to view a certain document, such as a timetable, the person who writes the timetable must have read, write, and execute permissions. We want some users to know the content of this timetable. , without letting them modify it, so we can put these users into a group, and then modify the permissions of this file to make it readable by the user group, so that every user under the user group can be readable;

The corresponding relationship between users and user groups is: one-to-one, many-to-one, one-to-many or many-to-many;
One-to-one: a user can be the only member of a group;
Many-to-one: Multiple users can be members of a unique group and do not belong to other user groups; for example, the two users beinan and linuxsir only belong to the beinan user group;
One-to-many: A user can be a member of many A member of a user group; for example, beinan can be a member of the root group, a member of the linuxsir user group, or a member of the adm user group;
Many-to-many: Multiple users correspond to multiple user groups, and several users It can belong to the same group; in fact, the many-to-many relationship is an extension of the previous three items; after understanding the above three items, this one can also be understood;

Tools or commands for managing user groups (groups) ：

groupadd 注：添加用户组；

groupdel 注：删除用户组；

groupmod 注：修改用户组信息

groups 注：显示用户所属的用户组

grpck grpconv 注：通过/etc/group和/etc/gshadow 的文件内容来同步或创建/etc/gshadow ，如果/etc/gshadow 不存在则创建；

grpunconv 注：通过/etc/group 和/etc/gshadow 文件内容来同步或创建/etc/group ，然后删除gshadow文件；

Related recommendations: "Linux Tutorial"

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