Linux system security management: detailed explanation of user accounts and permissions

Linux is known for its powerful stability and security. It is a multi-user operating system that allows multiple users to access system resources at the same time without interfering with each other. Effective user account and permission management is crucial to maintaining the security and efficiency of Linux systems. This article will explore in-depth how to effectively manage user accounts and permissions in Linux.

Understand user accounts in Linux

User accounts are the basis for a single user to access and operate Linux systems. They help resource allocation, permission setting, and protect the system from unauthorized access. There are two main types of user accounts:

• root account : This is a super user account with full access to all commands and files on the Linux system. The root account has supreme permissions and can perform any action, including operations that may harm the system, so it should be used with caution.
• Normal user accounts : These accounts have relatively limited permissions, usually only in the user's own home directory. The permission settings for these accounts are designed to protect the core functionality of the system from unexpected interruptions.

In addition, the Linux system also includes various system accounts for running Web servers, databases and other services.

Create and manage user accounts

Create a user account in Linux using the useradd or adduser command. adduser command is more interactive and user-friendly than the useradd command.

Create a new user sudo adduser 新用戶名

This command creates a new user account and its home directory and contains the default configuration file.

Set user attributes - Password : Use passwd command to set or change the password.

• Home directory : Use useradd -d /home/新用戶名新用戶名Specify the home directory when created.
• Log in to Shell : Use useradd -s /bin/bash 新用戶名to define the default shell.

Modify and delete user accounts - To modify an existing user, use usermod . For example, sudo usermod -s /bin/zsh 用戶名changes the user's default shell to zsh.

• To delete a user and its home directory, use userdel -r 用戶名.

Understand Linux permissions

In Linux, each file and directory has associated access rights that determine who can read, write, or execute them.

Understanding Permissions - Read (r) , Write (w) and Execute (x) permissions define three types of users: file owner, group, and other users.

• Permissions are displayed using the ls -l command, showing a 10-character string (for example, -rwxr-xr-- ), where each character represents a different access permission.

Ownership - Files and directories in Linux are owned by users and groups. Use chown to change owners, use chgrp to change groups.

Special permissions - setuid : Allows users to run executable files with permissions of the executable file owner.

• setgid : The file created in a directory with the setgid bit will inherit the group of that directory and run the executable file with the group permissions of the executable owner.
• Sticky bits : Usually seen in directories like /tmp , sticky bits allow files to be deleted only by their owner.

Management Group Membership

Groups in Linux are a way to organize users and define permissions for a group of users.

Create and manage groups - Create a new group using groupadd .

• Use usermod -aG 組名用戶名add the user to the group.
• You can also use the gpasswd tool to effectively manage group membership.

Advanced permission management

For more complex permission configurations, Linux supports access control lists (ACL), which allows for finer granular permission settings than traditional file ownership and permission schemes.

Use ACL - Set the ACL with setfacl , for example, setfacl -mu:用戶名:rwx 文件.

• Use getfacl 文件to view the ACL.

User activity automation and monitoring

Automated account management tasks can greatly improve system management efficiency. Shell scripts, cron jobs, and system tools such as awk and sed can help automate routine tasks. Commands such as last , who , and w provide information about user login and help monitor who is accessing the system.

User Account Management Best Practices

• Regularly update and review user accounts.
• Implement strong password policies and use tools such as fail2ban to enhance security.
• Educate users about best security practices to minimize potential security breaches.

in conclusion

Effective user account and permission management is crucial to maintaining the security and efficiency of Linux systems. By understanding and implementing the policies outlined in this guide, system administrators can ensure that their Linux system is both secure and user-friendly.

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