The concept of Linux users and groups

I. Concepts of users and groups

1. Understanding Linux multiuser, multitasking features

Linux is a real, full multi-user multitasking operating system, multi-user multitasking is to build multiple users on the system, and multiple users can log on to the same system at the same time to perform their different tasks, without affecting each other, such as a Linux server has 4 users, is root, WWW, ftp and mysql, at the same time, the root user may be in the view of the system log, management maintenance system, WWW users may modify their own web programs, FTP users may upload software to the server, MySQL users may execute their own SQL query, each user non-interference, Methodically carry out their own work, and each user can not exceed the authority of access, such as the WWW users can not perform the MySQL user SQL query operations, FTP users can not modify the WWW user's Web program, so that different users have different permissions, Each user is in the scope of permission to complete a different task, Linux is through the division and management of permissions, the implementation of a multi-user multitask operation mechanism.

2. User's role classification under Linux

Under Linux, users are defined by roles and are divided into three different roles:

Superuser: Has the highest administrative privileges on the system, and the default is root user.

Ordinary users: Only the files under their own directory access and modification, with login system permissions, such as the above mentioned WWW users, FTP users.

Virtual User: Also known as "pseudo" user, this type of user is the biggest feature is unable to log on to the system, their existence is mainly convenient system management, to meet the corresponding system process for the document owner requirements. For example, the system default bin, ADM, nobody user, and so on, generally run Web services, the default is the use of nobody users, but nobody users can not log on to the system.

3. Concepts for users and groups

We know that Linux is a multi-user multitasking operating system, if you want to use system resources, you must apply to the system administrator an account, and then through the account into the system. This account and user is a concept, through the establishment of different attributes of the user, on the one hand, can be reasonable use and control of system resources, on the other hand, can also help users organize files to provide security protection for user files.

Each user uses a unique username and user password to enter the system and its home directory only if the user name and password are entered correctly when logging on to the system.

A user group is a logical collection of users with the same characteristics. Sometimes we need to have multiple users have the same permissions, such as view, modify the permissions of a file, one way is to multiple users file access authorization, if there are 10 users, you need to authorize 10 times, obviously this method is not very reasonable The other way is to set up a group that has permission to view and modify this file, and then put all users who need access to the file into the group, so that all users have the same permissions as the group. This is the user group, a group of users is a Linux system for users to manage and control access to the means, by defining user groups, to a large extent simplifies the management work.

4. User and group relationships:

The corresponding relationship between user and user group is: pair of one or one pairs, multiple pairs of one and many-to-many; The following illustration shows this relationship:

One-to-one: A user can exist in a group, or it can be a unique member of a group.

One-to-many: A user can exist in more than one user group. Then this user has common permissions for multiple groups.

Many-to-many: Multiple users can exist in a group that has the same permissions as the group.

Many-to-many: Multiple users can exist in more than one group. is actually the extension of the above three corresponding relationships.