change the permissions of a file or directory. in the unix system family, the control of file or directory permissions is divided into three general permissions: read, write, and execute. there are also three special permissions available for use, and the scope of management permissions is matched with the owner and the group to which it belongs. you can use the chmod command to change the permissions of files and directories. the setting method can be text or numerical codes. the permissions of a symbolic link cannot be changed. if you modify the permissions of a symbolic link, the changes will be applied to the original file being connected. the representation of permission scope is as follows:

u: user, the owner of the file or directory.

g: group, that is, the group to which the file or directory belongs.

o: other, except the file or directory owner or the group to which it belongs, all other users belong to this scope.

a: all, that is, all users, including owners, groups and other users.

the relevant permission codes are listed below:

r: read permission, number code is "4".

w: write permission, the number code is "2".

x: execute or switch permissions, the numerical code is "1".

-: does not have any permissions, and the digital code is "0".

s: special? b> function description: change the permissions of a file or directory.