In the UNIX system family, the control of file or directory permissions is divided into three general permissions: Read, Write, and Execute. There are 3 special permissions available for use. And the group management authority range. You can use the CHMOD command to change the permissions o f files and directories. The setting method can be either text or numeric code. The permissions of the symbolic link cannot be changed. If you modify the permissions on the symbolic link, the changes will be applied to the original file being connected. The representation of the scope of authority is as follows:

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

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

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

a: All, that is, all users, including owners, groups, and other users.   For the part of the permission code, the list is as follows:

r: Read permission, the number code is "40"

w: Write permission, the number code is "2"

x: Execute or switch permissions, the number code is "10"

-: does not have any permissions, the number code is "0"

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