Explanation of chmod command for modifying directory permissions

The chmod command is used to modify the permissions of a file or directory. It stands for change mode.

Syntax:
chmod [options]… permissions… filename…

常用选项:
-R: Recursively modify the permissions of files in a directory and its subdirectories.

Commonly used permissions:
u: represents the owner of the file or directory.
g: represents users in the same group as the owner of the file or directory.
o: represents other users.
a: represents all users.

Common permission symbols:
+ : Add permission.
– : Remove permission.
= : Set permission.

常用权限：
r：读取。
w：写入。
x：执行。

Example:

The example can be found in the textbook.

1. Change the permissions of all users for the file file.txt to read-only by running:
   chmod a-w file.txt
2. Change the permissions of all users for the file file.txt to read-only and recursively modify the permissions of files in its subdirectories.
3. Change the owner’s permissions of file.txt to read, and remove read and write permissions for the group and others:
   chmod u=r,go-rw file.txt
4. Set the owner and group users of directory dir to have read and write permissions, while keeping the permissions for other users unchanged:
   chmod ug=rw dir

Important notes:

1. There are three types of permissions: user, group, and others. Each type consists of three permissions: read, write, and execute.
2. Permissions can be separated by commas or written in a continuous line.
3. When changing directory permissions, using the -R option will recursively modify permissions for the directory and its subdirectories.
4. When modifying permissions, symbols can be used to indicate adding, removing, and setting permissions.