Improve Linux system security: optimize and adjust file permission settings

How to optimize and adjust the file permission settings of Linux systems to improve security

Introduction
In today’s digital age, data security is crucial. For Linux systems, file permission settings are a key security measure, which can effectively protect important system data from being accessed or tampered with by unauthorized personnel. This article will introduce how to optimize and adjust the file permission settings of Linux systems to improve security.

1. Understand file permissions
Before we start optimizing and adjusting file permissions, we need to understand the basic concepts of file permissions. In a Linux system, every file and directory has three basic permissions: read (r), write (w), and execute (x). These permissions can be set between users (owners), user groups (groups) and other users (others) respectively. By setting these permissions correctly, we can ensure that only authorized users can access and modify files.

2. Use the principle of least privileges
The "principle of least privileges" is one of the important principles for setting file permissions. This means we should assign minimal permissions to each user and user group to prevent unnecessary file access and modification. Users are given only the permissions they need based on their needs, rather than giving them all permissions. This reduces the opportunities for potential attackers and increases the security of your system.

3. Follow the correct ownership and group settings
Correct ownership and group settings are very important to restrict specific users' access to files. Every file and directory has an owner and a group that belongs to a specific group. With the correct settings, we can ensure that only the owner and group members have access to the file.

We can use the chown command to change the owner of a file or directory, for example:

chown user1 file1

We can also use the chgrp command to change the group of a file or directory, for example:

chgrp group1 file1

4. Use the chmod command correctly
The chmod command is the key command to adjust file permissions. It can use numbers or symbols to represent permission settings. The following are some commonly used chmod command examples:

1) Use numbers to represent permissions

chmod 644 file1  #设置文件所有者为读写，组和其他用户为只读 
chmod 755 dir1  #设置目录所有者为读写执行，组和其他用户为读执行

2) Use symbols to represent permissions

chmod u=rw,g=r,o=r file1  #设置文件所有者为读写，组和其他用户为只读 
chmod u=rwx,g=rx,o=rx dir1  #设置目录所有者为读写执行，组和其他用户为读执行

Using the chmod command correctly can ensure that only authorized users Able to perform specific operations to improve system security.

5. Use ACL (Access Control List)
In addition to basic Linux file permission settings, we can also use ACL (Access Control List) to more accurately control access permissions to files and directories. ACL allows us to set permissions for multiple users and groups on a single file or directory. We can use the setfacl and getfacl commands to add, delete and modify ACLs.

For example, we can use the setfacl command to add read and write permissions to user 1:

setfacl -m u:user1:rw file1

Use the getfacl command to view the ACL settings of a file or directory:

getfacl file1

6. Regularly review permission settings
File permission settings are not a one-time task, but require regular review and adjustment. We should regularly check permissions on files and directories and remove access permissions from users and groups that are no longer needed. This ensures that the system is always in optimal security.

Conclusion
By optimizing and adjusting the file permission settings of the Linux system, we can effectively improve the security of the system. Using the principle of least privilege, following correct ownership and group settings, using the chmod command correctly, and using ACLs for more granular permission control can help us prevent potential attacks and protect the system's important data. At the same time, we should also regularly review permission settings to ensure that the system is always maintained in an optimal security state.

Reference materials:

1. Linux permission setting guide: https://www.thegeekstuff.com/2010/04/unix-file-and-directory-permissions/
2. Use ACL to manage file permissions: https://linux.die.net/man/1/setfacl

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