What is the purpose of the chmod command in Linux?

The chmod command is used to change the permissions of a file or directory.

It allows users to set permissions for files or directories, such as read, write, and execute permissions, as well as special permissions like setting the file’s owner and group, setting the file’s sticky bit, etc.

The usage of the chmod command is as follows:
chmod [options] mode file_name

常见的选择包括：

1. – R: Recursively change the permissions of files in directories and their subdirectories.
2. -v: Display information about modified file permissions.
3. -c: Show only the file permission information that has changed.

Common patterns include:

1. Numeric mode: Three numbers represent permissions, with the first digit indicating the owner’s permissions, the second digit indicating the group’s permissions, and the third digit indicating others’ permissions. Each digit is represented by a number ranging from 0 to 7, where 0 means no permission and 7 means full permission. For example, the command chmod 755 file sets the permissions for file to -rwxr-xr-x.
2. Symbolic notation: Using symbols to represent permissions, including u (user), g (group), o (other clients), and a (all users), etc. + denotes adding permissions, – denotes removing permissions, = denotes setting specific permissions. For example, the command chmod u+x file adds owner execute permission to the file.

Using the chmod command, users can adjust the permissions of files or directories as needed to protect the security and privacy of the files.