Detailed introduction to users and user groups in Linux

Users and user groups are very important in the Linux system. As the super administrator of the system, root, should manage the users and user groups in the current operating system well. The reason is very simple. If you can't manage users and user groups well, how can you manage the entire server?

User: People who use the operating system

User group: A group of users with the same system permissions

Home directory: also called the home directory, is where the user logs in to the system The directory entered by default, and the user's home directory permissions belong to the user

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Related configuration files

/etc/group Stores all user group information in the current system.

Each line of the file content represents a user group. The information format of each user group is fixed. The information description is as shown in the figure:

1. root user group The group number is fixed at 0

2. All group password placeholders are replaced by software or services used on. The earlier the software or service is installed, the smaller the group number assigned to it. Generally, the smallest unallocated group number is assigned to the installed software or service.

4. The user group number manually created by the user starts from 500. Generally, the smallest group number that is greater than or equal to 500 and is not used is assigned.

5. The user name list in the group is empty. There may be no user or only one user and the user name and group name are consistent

/etc/gshadow

Stores the password information of the user group in the current system. The number of lines in the gshadow configuration file is the same as that in the group file, and each line corresponds to each line in the group one-to-one. The description of each line is as follows:

1. If the group password is empty or has an exclamation mark or *, it means that the group has no password

2. The group manager is Empty, indicating that each member of the group can manage the group

/etc/passwd

Stores the information of all users in the current system. Each line of the file content represents a user's configuration information. The format of each user's information is fixed. The information description is as shown in the figure:

1. root user The number is fixed at 0

2. For other users except the root user, when the user is created, a directory with the same user name will be created for the user in the /home directory as the user's home directory.

/etc/shadow

Stores the password information of all users in the current system. The number of lines of the shadow configuration file is the same as that of the passwd file, and each line corresponds to each line of passwd one-to-one. The content of each line is explained as follows:

1. User passwords are generally encrypted by a one-way encryption algorithm, and it is impossible to directly see what the original password is.

2. In addition to the user name and password, the content also includes the creation time of the user, the last time the user information was modified, etc. There is no need to delve into it.

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