How to set file permissions on Linux

How to set file permissions on Linux

In the Linux system, file permissions are very important, which determines the user's access level to the file. File permissions are divided into three parts: Owner, Group, and Others. By setting appropriate file permissions, you can ensure that only authorized users can access or modify files. The following will introduce how to set file permissions on Linux and provide some example code for reference.

1. View current file permissions
   Before starting to set file permissions, we need to check the permissions of the current file. You can use the ls -l command to list detailed file information, including file permission information. For example, if we want to view the permissions of file example.txt, we can run the following command:

   ls -l example.txt

   This will output something similar to the following:

   -rw-r--r-- 1 user group 0 Jan 1 2022 example.txt

   where, rw-r--r-- indicates the permissions of the file. The first character - indicates that this is an ordinary file. If it is a directory, it is displayed as d. The next three characters rw- represent the permissions of the file owner, the next three characters r-- represent the permissions of the group to which the file belongs, and the last three characters r-- indicates the permissions of others.

2. Set file permissions
   Setting file permissions mainly uses the chmod command. The basic syntax of the chmod command is:

   chmod [权限模式] 文件名

   Permission mode can be expressed using numeric mode or symbolic mode.

• #Set permissions using numeric mode
  Numeric mode is the most common way to set file permissions. Each file permission is represented by a number, read permission is 4, write permission is 2, and execute permission is 1. Permissions for owners, groups, and others are represented by three digits. For example, to set the permissions of file example.txt to read-write for the owner, and read-only for the group and others, you can run the following command:

  chmod 644 example.txt

  This will change the file ## The permissions of #example.txt are set to -rw-r--r--.

• Use symbolic mode to set permissions

  Symbolic mode is more intuitive and easy to remember, it uses plus sign () and minus sign (-) to add and remove permissions. Here are some examples of symbolic patterns:
  

  Add permissions:
  • means add permissions.
  Delete permission:
  • - means delete permission.
  A certain permission:
  • r means read permission, w means write permission, x means execution permission.
  Owner, Group and Others:
  • u for owner, g for group, o for others, a means everyone.

For example, to set the permissions of file

example.txt to be writable by the owner and read-only by the group and others, you can run the following command:

chmod u+w,go-w example.txt

This will set the permissions of the file

example.txt to -rw-r--r--.

Example code example
3. The following is some example code for setting file permissions:
   

• Set the file owner to be readable and writable, and the group Read-only for group and others:

  chmod 644 example.txt

• Set the file owner to read, write and execute, group and others read-only and execute:

  chmod 755 script.sh

• Add execute permissions for file owners and groups:

  chmod +x script.sh

• Remove file write permissions for others:

  chmod o-w example.txt

Via these Example code makes it easy to set file permissions as needed.

Summary

File permissions play a vital role in Linux systems. By correctly setting file permissions, you can ensure the security and accessibility of files. This article explains how to set file permissions on Linux and provides some example code for reference. By learning and mastering how to set file permissions, you can better protect file security.

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