Update 586-file-chmod.markdown

Author: Joe7M

_build/reference/586-file-chmod.markdown

@@ -7,11 +7,33 @@ Change permissions of a file. See also ACCESS.
 * file - A string expression that follows OS file naming conventions.
 * mode - Compatible with system call chmod()'s 'mode' parameter.
 
+Linux:
+
+mode is a number best represented in octal: 0oUGO with U: User; G: Group; O: Other 
+
+U, G and O are each defined the following way:
+
+| Value | Permission  |
+|:-----:|:-----------:|
+| 0     | 	no        |
+| 1 	  | x (execute) |
+| 2 	  | w (write)   |
+| 3 	  | w + x       |
+| 4 	  | r (read)    |
+| 5 	  | r + x       |
+| 6 	  | r + w       |
+| 7 	  | r + w + x   |
+
+
 ```
 ' Make myfile available to anyone (read/write)
 CHMOD "myfile.bas", 0o666
-...
+
 ' Make myfile available to anyone (execute/read/write)
 CHMOD "myfile.bas", 0o777
+
+' Make myfile available to user (read/write)
+' All others only read
+CHMOD "myfile.bas", 0o644
 ```