Analyze Linux user ID classification and usage

Linux user ID classification and usage analysis

In the Linux system, each user has a unique user ID (UID) and a group ID (GID) , these IDs are used to identify users and determine their permissions and user groups to which they belong. In this article, we will analyze the classification and uses of user IDs in Linux in detail, and provide specific code examples.

1. User ID classification

1. System user:
   System user is a special user used to run system services and processes. They usually do not have login permissions, and the UID value is usually Smaller (usually between 0-999). The role of the system user is to ensure the security of system services and avoid overlapping IDs with ordinary users.
2. Ordinary users:
   Ordinary users are ordinary users in the system. They usually have login permissions and can perform various operations. UID values ​​for ordinary users usually start at 1000 and increase according to the order of creation.
3. Special users:
   Special users usually refer to super users (root) and group (wheel) members, who have the highest level of permissions in the system. The UID of the super user is 0, and the UID of the group (wheel) members can be customized as needed.

2. Analysis of user ID usage

1. Determine user permissions:
   User ID plays a vital role in the Linux system. It determines the user's rights. Read, write, and execute permissions for files and directories. Through UID and GID, the system can effectively manage file access control and ensure data security.
2. Switch user identity:
   In Linux systems, you can use the su or sudo command to switch user identities. These commands rely on the user ID to determine whether the user has permission to perform a specific action. For example, using sudo allows ordinary users to temporarily gain superuser privileges to perform specific tasks.
3. Determine the file owner:
   Each file or directory has an owner and group in the system, and this information is determined by the user ID. The user ID allows the system to identify the owner of a file and determine its permissions.

Code example:

1. Command to view the current user ID and group ID:

   id

   Copy after login

2. Create one System user and specify UID:

   sudo useradd -r -u 5000 myuser

   Copy after login

3. Modify file owner and group:

   chown myuser:mygroup myfile.txt

   Copy after login

Summary:

User ID It plays a vital role in the Linux system. It not only determines the user's permissions, but also affects the security and access control of the system. By analyzing the classification and uses of user IDs, we can better understand the principles of user management in Linux systems and perform permission control and identity switching more effectively.

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