Octal and Binary Representations of Permissions

Imagine the rwx permissions as three ON/OFF switches, so when all permissions are granted, this equates to 111 in binary. Each file or directory has three basic permission types:

read – The Read permission refers to a user’s capability to read the contents of the file.
write – The Write permissions refer to a user’s capability to write or modify a file or directory.
execute – The Execute permission affects a user’s capability to execute a file or view the contents of a directory.

(000) 0 = No Permission
(001) 1 = Execute
(010) 2 = Write
(100) 4 = Read

Binary	Octal	rwx
000	0	---
001	1	--x
010	2	-w-
011	3	-wx
100	4	r--
101	5	r-x
110	6	rw-
111	7	rwx

Ref: https://linuxfoundation.org/blog/classic-sysadmin-understanding-linux-file-permissions/