Change the permissions of a file or directory. In the UNIX family of systems, file or directory permissions are controlled by three general permissions: read, write, and execute. There are also three special permissions that can be used, and the owner and the group to which they belong manage the permission range. You can use the chmod command to change the permissions of files and directories. The setting method can be text or numeric codes. The permissions of symbolic links cannot be changed. If you modify the permissions of a symbolic link, the changes will affect the original file to which it is connected. The permission range is expressed 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 for the file or directory owner or the group to which it belongs, all other users belong to this range.

a：All, that is, all users, including the owner, the group to which they belong, and other users.

The following are the parts about the permission codes:

r: Read permission, the numeric code is "4".

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

x: Execute or switch permissions, the numeric code is "1".

-: No permissions, the numeric code is "0".

s: Special?b>Function description: Change the permissions of files or directories.